FEL2019 - List of Keywords (FEL)

Paper	Title	Other Keywords	Page
MOA02	First Lasing of a Free Electron Laser in the Soft X-Ray Spectral Range with Echo Enabled Harmonic Generation	laser, electron, experiment, free-electron-laser	7
	E. Allaria, A. Abrami, L. Badano, M. Bossi, N. Bruchon, F. Capotondi, D. Castronovo, M. Cautero, P. Cinquegrana, M. Coreno, I. Cudin, M.B. Danailov, G. De Ninno, A.A. Demidovich, S. Di Mitri, B. Diviacco, W.M. Fawley, M. Ferianis, L. Foglia, G. Gaio, F. Giacuzzo, L. Giannessi, S. Grulja, F. Iazzourene, G. Kurdi, M. Lonza, N. Mahne, M. Malvestuto, M. Manfredda, C. Masciovecchio, N.S. Mirian, I. Nikolov, G. Penco, E. Principi, L. Raimondi, P. Rebernik Ribič, R. Sauro, C. Scafuri, P. Sigalotti, S. Spampinati, C. Spezzani, L. Sturari, M. Svandrlik, M. Trovò, M. Veronese, D. Vivoda, M. Zaccaria, D. Zangrando, M. Zangrando Elettra-Sincrotrone Trieste S.C.p.A., Basovizza, Italy H.-H. Braun, E. Ferrari, E. Prat, S. Reiche PSI, Villigen PSI, Switzerland N. Bruchon University of Trieste, Trieste, Italy M. Coreno CNR-ISM, Trieste, Italy M.-E. Couprie, A. Ghaith SOLEIL, Gif-sur-Yvette, France G. De Ninno University of Nova Gorica, Nova Gorica, Slovenia C. Feng SARI-CAS, Pudong, Shanghai, People’s Republic of China F. Frassetto, L.P. Poletto LUXOR, Padova, Italy D. Garzella CEA, Gif-sur-Yvette, France V. Grattoni DESY, Hamburg, Germany E. Hemsing SLAC, Menlo Park, California, USA P. Miotti CNR-IFN, Padova, Italy G. Penn LBNL, Berkeley, California, USA M.A. Pop MAX IV Laboratory, Lund University, Lund, Sweden E. Roussel PhLAM/CERCLA, Villeneuve d’Ascq Cedex, France T. Tanikawa EuXFEL, Schenefeld, Germany D. Xiang Shanghai Jiao Tong University, Shanghai, People’s Republic of China
	We report on the successful operation of a Free Electron Laser (FEL) in the Echo Enabled Harmonic Generation (EEHG) scheme at the FERMI facility at Sincrotrone Trieste. The experiment required a modification of the FEL-2 undulator line which, in normal operation, uses two stages of high-gain harmonic generation separated by a delay line. In addition to a new seed laser, the dispersion in the delay-line was increased, the second stage modulator changed and a new manipulator installed in the delay-line chicane hosting additional diagnostic components. With this modified setup we have demonstrated the first evidence of strong exponential gain in a free electron laser operated in EEHG mode at wavelengths as short as 5 nm.
	Slides MOA02 [5.133 MB]
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-FEL2019-MOA02
About •	paper received ※ 21 August 2019 paper accepted ※ 28 August 2019 issue date ※ 05 November 2019
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MOA03	First Lasing at the CAEP THz FEL Facility	electron, laser, free-electron-laser, high-voltage	11
	P. Li, T.H. He, M. Li, J. Liu, X. Luo, Q. Pan, L.J. Shan, X. Shen, H. Wang, J. Wang, D. Wu, D.X. Xiao, Y. Xu, L.G. Yan, P. Zhang, K. Zhou CAEP/IAE, Mianyang, Sichuan, People’s Republic of China Y. Liu CAEP/IFP, Mainyang, Sichuan, People’s Republic of China
	China Academy of Engineering Physics terahertz free electron laser (CAEP THz FEL, CTFEL) is the first THz FEL user facility in China, which was an oscillator type FEL. This THz FEL facility consists of a GaAs photocathode high-voltage DC gun, a superconducting RF linac, a planar undulator and a quasi-concentric optical resonator. The terahertz laser’s frequency is continuous adjustable from 0.7 THz to 4.2 THz. The average power is more than 10 W and the micro-pulse power is more than 0.3 MW. In this paper, the specific parameters and operation status of CTFEL are presented. Finally, some user experiments are introduced briefly.
	Slides MOA03 [3.771 MB]
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-FEL2019-MOA03
About •	paper received ※ 20 August 2019 paper accepted ※ 18 September 2019 issue date ※ 05 November 2019
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MOA07	Commissioning and First Lasing of the FELiChEM: A New IR and THz FEL Oscillator in China	electron, cavity, undulator, linac	15
	H.T. Li, Q.K. Jia USTC/NSRL, Hefei, Anhui, People’s Republic of China
	A new infrared FEL named FELiChEM aiming at the energy chemistry has been constructed and commissioned at NSRL in Hefei. It consists of two FEL oscillators driven by one normal-conducting S-Band linac with maximum beam energy of 60 MeV. The two oscillators generate the midinfrared and far-infrared lasers covering the spectral range of 2.5-50 µm and 40-200 µm, respectively. First lasing was achieved at a wavelength of 15 µm with an electron energy of 35 MeV. Till now, we have observed the FEL signal from 3.5 µm to 30 µm and achieved the maximum micropulse energy up to 27 µJ at 15 µm.
	Slides MOA07 [2.434 MB]
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-FEL2019-MOA07
About •	paper received ※ 20 August 2019 paper accepted ※ 28 August 2019 issue date ※ 05 November 2019
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MOC01	Regenerative Amplifier FEL - from IR to X-Rays	cavity, undulator, electron, feedback	20
	D.C. Nguyen, P.M. Anisimov, C.E. Buechler, Q.R. Marksteiner, R.L. Sheffield LANL, Los Alamos, New Mexico, USA
	The Regenerative Amplifier FEL (RAFEL) feeds back a small fraction of the radiation exiting a high-gain undulator as the seed for the next pass, and achieves narrow linewidth and saturation in a few passes. For the IR RAFEL, we used an optical cavity with annular mirrors to reinject ~10% of the IR radiation back into a two-meter undulator [1]. Since then, a number of researchers have proposed RAFEL and XFELO to achieve full temporal coherence in VUV and X-ray FELs [2-5]. For the XFELO, symmetric Bragg backscattering off high-quality diamond crystals can provide very high reflectivity for the XFELO cavity [6]. The required reflectivity for a RAFEL feedback cavity is much lower than the XFELO. We show that 6% feedback is sufficient for the X-ray RAFEL at 9.8 keV to saturate and achieve 0.5-eV bandwidth. We discuss options to out-couple more than ~50% of the RAFEL intra-cavity power and discuss challenges associated with X-ray absorption in the out-coupler. [1] D. Nguyen et al. NIMA 429 125 (1999) [2] B. Faatz et al. NIMA A429 424 (1999) [3] Z. Huang et al. PRL 96 144801 (2006) [4] B.W.J. McNeil et al. NJP 9 239 (2007) [5] G. Marcus et al. FEL17 MOP061 (2017) [6] K. Kim et al. PRL 100 244802 (2008)
	Slides MOC01 [1.260 MB]
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-FEL2019-MOC01
About •	paper received ※ 21 August 2019 paper accepted ※ 28 August 2019 issue date ※ 05 November 2019
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TUA01	Parallel Operation of SASE1 and SASE3 at the European XFEL	background, operation, electron, undulator	25
	S. Liu, F. Brinker, W. Decking, L. Fröhlich, R. Kammering, D. Nölle, F. Obier, E. Schneidmiller, M. Scholz, T. Wilksen, M.V. Yurkov DESY, Hamburg, Germany R. Boll, N. Gerasimova, T. Mazza, M. Meyer, A. Scherz, H. Sinn EuXFEL, Schenefeld, Germany
	At the European XFEL a hard X-Ray SASE FEL (SA-SE1) and a soft X-Ray SASE FEL (SASE3) share in series the same electron beamline. This configuration couples the operation conditions for both undulators and their subsequent user experiments in terms of SASE in-tensity and background. We report on our experience in parallel operation and discuss the solutions that enable the operation of both undulators as independently as possible.
	Slides TUA01 [13.809 MB]
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-FEL2019-TUA01
About •	paper received ※ 26 August 2019 paper accepted ※ 17 October 2019 issue date ※ 05 November 2019
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TUA04	Harmonic Lasing Experiment at the European XFEL	undulator, electron, laser, free-electron-laser	29
	E. Schneidmiller, F. Brinker, W. Decking, M.W. Guetg, S. Liu, D. Nölle, M. Scholz, M.V. Yurkov, I. Zagorodnov DESY, Hamburg, Germany G. Geloni, N. Gerasimova, J. Grünert, S. Karabekyan, N.G. Kujala, J. Laksman, Y. Li, J. Liu, Th. Maltezopoulos, I. Petrov, L. Samoylova, S. Serkez, H. Sinn, F. Wolff-Fabris EuXFEL, Schenefeld, Germany
	Harmonic lasing is an opportunity to extend the photon energy range of existing and planned X-ray FEL user facilities. Contrary to nonlinear harmonic generation, harmonic lasing can provide a much more intense, stable, and narrow-band FEL beam. Another interesting application is Harmonic Lasing Self-Seeding (HLSS) that allows to improve the longitudinal coherence and spectral power of a Self-Amplified Spontaneous Emission (SASE) FEL. This concept was successfully tested at FLASH in the range of 4.5 - 15 nm and at PAL XFEL at 1 nm. In this contribution we present recent results from the European XFEL where we successfully demonstrated operation of HLSS FEL at 5.9 Angstrom and 2.8 Angstrom, in the latter case obtaining both 3rd and 5th harmonic lasing.
	Slides TUA04 [1.174 MB]
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-FEL2019-TUA04
About •	paper received ※ 20 August 2019 paper accepted ※ 29 August 2019 issue date ※ 05 November 2019
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TUB01	Echo-Enabled Harmonic Generation Lasing of the FERMI FEL in the Soft X-Ray Spectral Region	laser, electron, free-electron-laser, photon	33
	P. Rebernik Ribič Elettra-Sincrotrone Trieste S.C.p.A., Basovizza, Italy P. Rebernik Ribič University of Nova Gorica, Nova Gorica, Slovenia
	The layout of the FERMI FEL-2 undulator line, normally operated in the two-stage high-gain harmonic generation (HGHG) configuration, was temporarily modified to allow running the FEL in the echo-enabled harmonic generation (EEHG) mode. The EEHG setup produced stable, intense and nearly fully coherent pulses at wavelengths as short as 5.9 nm (211 eV). Comparing the performance to the two-stage HGHG showed that EEHG gives significantly better spectra in terms of the central wavelength stability and bandwidth, especially at high harmonics, where electron-beam imperfections start to play a significant role. Observation of stable, narrow-band, coherent emission down to 2.6 nm (474 eV) indicates the possibility to extend the lasing region to even shorter wavelengths.
	Slides TUB01 [10.360 MB]
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-FEL2019-TUB01
About •	paper received ※ 21 August 2019 paper accepted ※ 29 August 2019 issue date ※ 05 November 2019
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TUP001	Extension of the PITZ Facility for a Proof-of-Principle Experiment on THz SASE FEL	radiation, undulator, electron, experiment	38
	P. Boonpornprasert, G.Z. Georgiev, G. Koss, M. Krasilnikov, X. Li, F. Mueller, A. Oppelt, S. Philipp, H. Shaker, F. Stephan, T. Weilbach DESY Zeuthen, Zeuthen, Germany Z.G. Amirkhanyan CANDLE SRI, Yerevan, Armenia
	The Photo Injector Test Facility at DESY in Zeuthen (PITZ) has been proposed as a suitable facility for research and development of an accelerator-based THz source prototype for pump-probe experiments at the European XFEL. A proof-of-principle experiment to generate THz SASE FEL radiation by using an LCLS-I undulator driven by an electron bunch from the PITZ accelerator has been planned and studied. The undulator is foreseen to be installed downstream from the current PITZ accelerator, and an extension of the accelerator tunnel is necessary. Radiation shielding for the extended tunnel was designed, and construction works are finished. Design of the extended beamline is ongoing, not only for this experiment but also for other possible experiments. Components for the extended beamline, including magnets for beam transport, a chicane bunch compressor, electron beam diagnostics devices, and THz radiation diagnostics devices have been studied. An overview of these works will be presented in this paper.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-FEL2019-TUP001
About •	paper received ※ 20 August 2019 paper accepted ※ 28 August 2019 issue date ※ 05 November 2019
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TUP002	Progress in Preparing a Proof-of-Principle Experiment for THz SASE FEL at PITZ	laser, undulator, experiment, flattop	41
	X. Li, P. Boonpornprasert, Y. Chen, G.Z. Georgiev, J.D. Good, M. Groß, P.W. Huang, I.I. Isaev, C. Koschitzki, M. Krasilnikov, S. Lal, O. Lishilin, G. Loisch, D. Melkumyan, R. Niemczyk, A. Oppelt, H.J. Qian, H. Shaker, G. Shu, F. Stephan, G. Vashchenko DESY Zeuthen, Zeuthen, Germany
	A proof-of-princle experiment for a THz SASE FEL is undergoing preparation at the Photo Injector Test facility at DESY in Zeuthen (PITZ), as a prototype THz source for pump-probe experiments at the European XFEL, which could potentially provide up to mJ/pulse THz radiation while maintaining the identical pulse train structure as the XFEL pulses. In the proof-of-principle experiment, LCLS-I undulators will be installed to generate SASE radiation in the THz range of 3-5 THz from electron bunches of 16-22 MeV/c. One key design is to obtain the peak current of nearly 200 A from the heavily charged bunches of a few nC. In this paper, we report our simulation results on the optimization of the space charge dominated beam in the photo injector and the following transport line with two cathode laser setups. Experimental results based on a short Gaussian laser will also be discussed.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-FEL2019-TUP002
About •	paper received ※ 20 August 2019 paper accepted ※ 27 August 2019 issue date ※ 05 November 2019
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TUP003	Design of a Magnetic Bunch Compressor for the THz SASE FEL Proof-of-Principle Experiment at PITZ	radiation, dipole, experiment, undulator	45
	H. Shaker, P. Boonpornprasert, G.Z. Georgiev, G. Koss, M. Krasilnikov, X. Li, A. Lueangaramwong, F. Mueller, A. Oppelt, S. Philipp, F. Stephan, G. Vashchenko, T. Weilbach DESY Zeuthen, Zeuthen, Germany
	For pump-probe experiments at the European XFEL, a THz source is required to produce intense THz pulses at the same repetition rate as the X-ray pulses from XFEL. Therefore, an accelerator-based THz source with identical electron source as European XFEL was suggested and proof-of-principle experiments utilizing an LCLS I undulator will be performed at the Photo Injector Test Facility at DESY in Zeuthen (PITZ). The main idea is to use a 4nC beam for maximum SASE radiation but to allow different radiation regimes a magnetic bunch compressor can be used. This helps e.g. to reduce the saturation length inside the undulator and also to study super-radiant THz radiation. In this paper a design of a chicane type magnetic bunch compressor using HERA corrector magnets is presented.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-FEL2019-TUP003
About •	paper received ※ 20 August 2019 paper accepted ※ 27 August 2019 issue date ※ 05 November 2019
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TUP004	A Superradiant THz Undulator Source for XFELs	undulator, electron, radiation, experiment	48
	T. Tanikawa, G. Geloni, S. Karabekyan, S. Serkez EuXFEL, Schenefeld, Germany V.B. Asgekar University of Pune, Pune, India S. Casalbuoni KIT, Eggenstein-Leopoldshafen, Germany M. Gensch Technische Universität Berlin, Berlin, Germany M. Gensch DLR, Berlin, Germany S. Kovalev HZDR, Dresden, Germany
	The European XFEL has successfully achieved first lasing in 2017 and meanwhile three SASE FEL beamlines are in operation. An increasing number of users has great interest in a specific type of two-color pump-probe experiments in which high-field THz pulses are employed to drive nonlinear processes and dynamics in matter selectively. Here, we propose to use a 10-period superconducting THz undulator to provide intense, narrowband light pulses tunable in wide range between 3 and 100 THz. The exploitation of superconducting technology allows us to meet the challenge of generating such low photon energy radiation despite the very high electron beam energy at the European XFEL. In this presentation, we will present the latest development concerning THz undulator design and present the expected THz pulse properties for the case of the European XFEL.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-FEL2019-TUP004
About •	paper received ※ 20 August 2019 paper accepted ※ 27 August 2019 issue date ※ 05 November 2019
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TUP006	The FHI FEL Upgrade Design	undulator, cavity, dipole, kicker	52
	W. Schöllkopf, M. De Pas, D. Dowell, S. Gewinner, H. Junkes, G. Meijer, G. von Helden FHI, Berlin, Germany W.B. Colson NPS, Monterey, California, USA S.C. Gottschalk STI Magnetics LLC, Woodinville, USA J. Rathke, T. Schultheiss AES, Medford, New York, USA A.M.M. Todd AMMTodd Consulting, Princeton Junction, New Jersey, USA L.M. Young LMY Technology, Lincolnton, Georgia, USA
	Since coming on-line in November 2013, the Fritz-Haber-Institut (FHI) der Max-Planck-Gesellschaft (MPG) Free-Electron Laser (FEL) has provided intense, tunable infrared radiation to FHI user groups. It has enabled experiments in diverse fields ranging from bio-molecular spectroscopy to studies of clusters and nanoparticles, nonlinear solid-state spectroscopy, and surface science, resulting in 50 peer-reviewed publications so far. A significant upgrade of the FHI FEL is now being prepared. A second short Rayleigh range undulator FEL beamline is being added that will permit lasing from < 5 microns to > 160 microns. Additionally, a 500 MHz kicker cavity will permit simultaneous two-color operation of the FEL from both FEL beamlines over an optical range of 5 to 50 microns by deflecting alternate 1 GHz pulses into each of the two undulators. We will describe the upgraded FHI FEL physics and engineering design and present the plans for two-color FEL operations in November 2020.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-FEL2019-TUP006
About •	paper received ※ 20 August 2019 paper accepted ※ 27 August 2019 issue date ※ 05 November 2019
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TUP008	Concept of High-Power CW IR-THz Source for the Radiation Source Elbe Upgrade	undulator, electron, radiation, linac	59
	P.E. Evtushenko, T.E. Cowan, U. Lehnert, P. Michel HZDR, Dresden, Germany
	The Radiation Source ELBE at HZDR is a user facility based on a 1 mA, 40 MeV CW SRF LINAC. HZDR is considering upgrade options for the ELBE or its replacement with a new user facility. A part of the user requirements is the capability to generate IR and THz pulse in the frequency range from 0.1 through 30 THz, with pulse energies in the range from 100 uJ through a few mJ, at the repetition rate between 100 kHz and 1 MHz. In this contribution, we outline key aspects of a concept, which would allow achieving such parameters. Such key aspects are: use of a beam with longitudinal density modulation and bunching factor of about 0.5 at the fundamental frequency; achieving the density modulation through the mechanism similar to the one used in optical klystron (OK) and HGHG FEL, generation necessary for the modulation optical beam by an FEL oscillator, using two electron injectors, where one injector provides a beam for the FEL oscillator while second high charge injector provides beam for the high energy per pulse generation for user experiments. All-in-all the concept of the new radiation source is very similar to an OK, but operating with two beams simultaneously.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-FEL2019-TUP008
About •	paper received ※ 29 August 2019 paper accepted ※ 29 August 2019 issue date ※ 05 November 2019
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TUP009	Integration of an XFELO at the European XFEL Facility	electron, radiation, simulation, cavity	62
	P. Rauer, I. Bahns, W. Hillert, J. Roßbach University of Hamburg, Institut für Experimentalphysik, Hamburg, Germany W. Decking DESY, Hamburg, Germany H. Sinn EuXFEL, Schenefeld, Germany
	Funding: Work supported by BMBF (FKZ 05K16GU4) An X-ray free-electron laser oscillator (XFELO) is a fourth generation X-ray source promising radiation with full three dimensional coherence, nearly constant pulse to pulse stability and more than an order of magnitude higher peak brilliance compared to SASE FELs. Proposed by Kim et al. in 2008 [1] an XFELO follows the concept of circulating the light in an optical cavity - as known from FEL oscillators in longer wavelength regimes - but uses Bragg reflecting crystals instead of classical mirrors. With the new European X-ray Free-Electron Laser (XFEL) facility recently gone into operation, the realization of an XFELO with radiation in the Angstrom regime seems feasible. Though, the high thermal load of the radiation on the cavity crystals, the high sensibility of the Bragg-reflection on reflection angle and crystal temperature as well as the very demanding tolerances of the at least 60 m long optical resonator path pose challenges which need to be considered. In this work these problems shall be summarized and results regarding the possible integration of an XFELO at the European XFEL facility will be presented. [1] K.-J. Kim, Y. Shvyd’ko and S. Reiche, Phys. Rev. Lett. 100 (2008), 244802.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-FEL2019-TUP009
About •	paper received ※ 20 August 2019 paper accepted ※ 29 August 2019 issue date ※ 05 November 2019
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TUP015	Design of High-Repetition Terahertz Super-Radiation Based on CAEP THz FEL Superconducting Beamline	radiation, electron, undulator, laser	73
	D. Wu, T.H. He, L.B. Li, M. Li, P. Li, X. Luo, Q. Pan, L.J. Shan, X. Shen, H. Wang, J. Wang, D.X. Xiao, L.G. Yan, P. Zhang, K. Zhou CAEP/IAE, Mianyang, Sichuan, People’s Republic of China
	China Academy of Engineering Physics terahertz free electron laser (CAEP THz FEL, CTFEL) is the first THz FEL oscillator in China. CTFEL spectrum covers from 0.7 THz to 4.2 THz. However, there are still many applications requiring lower frequency. The super-radiation of the ultra-short electron beam bunches could generate ultra-fast, carrier-envelope-phase-stable, and high-field terahertz. The coherent diffraction/transition radiation (CDR/CTR) and coherent undulator radiation (CUR) can be also synchronized naturally. In this paper, the dynamic and the design of the super-radiation are introduced. The main parameters of the CDR/CTR and CUR are also discussed. A multi-color pump-probe system based on super-radiation is also proposed. Work supported by National Natural Science Foundation of China with grant (11575264, 11605190 and 11805192), Innovation Foundation of CAEP with grant (CX2019036, CX2019037)
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-FEL2019-TUP015
About •	paper received ※ 20 August 2019 paper accepted ※ 27 August 2019 issue date ※ 05 November 2019
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TUP017	Terahertz FEL Simulation in PAL XFEL	electron, simulation, undulator, radiation	77
	J.H. Ko, H.-S. Kang PAL, Pohang, Republic of Korea
	Terahertz radiation is being used in various fields such as imaging, diagnosis, inspection, etc. For the terahertz research, the Pohang accelerator laboratory (PAL) is planning to make a terahertz free electron laser based on self-amplified spontaneous emission (SASE). Using free electron laser method, we can conduct the THz-pump X-ray probe experiment. For the terahertz free electron laser, we conducted the simulation on accelerators below 40 MeV, using photo-cathode RF gun, S-band accelerator and undulator below 4 meters.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-FEL2019-TUP017
About •	paper received ※ 20 August 2019 paper accepted ※ 25 August 2019 issue date ※ 05 November 2019
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TUP019	Regime of Multi-Stage Non-Resonant Trapping in Free Electron Lasers	electron, FEM, wiggler, experiment	83
	A.V. Savilov, I.V. Bandurkin, Yu.S. Oparina, N.Yu. Peskov IAP/RAS, Nizhny Novgorod, Russia
	Funding: This work is supported by the RFBR (grants #18-02-40009, #18-02-00765) and by the IAP RAS Project 0035-2019-0001. We describe three works united by the idea of the non-resonant regime [1] providing an effective trapping in a beam with a great energy spread. In this regime, the "bucket" corresponding to the resonant electron-wave interaction passes through the electron layer on the energy-phase plane and traps a fraction of electrons. (I) Operability of this regime was demonstrated in the high-efficient 0.8 MeV Ka-band FEM-amplifier [2]. (II) In short-wavelength FELs the multi-stage trapping in several consecutive sections can be organized [3]. In each section a small e-beam fraction is trapped due to a weak electron-wave interaction. However, repetition of this process from section to section involves in the interaction almost the whole e-beam. We describe efficiency enhancement and improving the frequency wave spectrum in multi-stage SASE FELs. (III) The multi-stage amplification of a single-frequency wave signal can provide cooling of the electron bunch. In this regime, tapering of every section is provided such that the "bucket" goes from maximal initial electron energy down to the minimal one and moves down energies of trapped electrons. [1] A.Savilov et al., Nucl. Instr. Meth. A, vol. 507, p.158, 2003 [2] A.Kaminsky et al., Int. Conf. IRMMW-THz 2018, art. 4057938 [3] S.Kuzikov, A.Savilov, Phys. Plasmas, vol. 25, p.113114, 2018
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-FEL2019-TUP019
About •	paper received ※ 14 August 2019 paper accepted ※ 27 August 2019 issue date ※ 05 November 2019
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TUP021	Development of Powerful Long-Pulse Terahertz Band FELs Based on Linear Induction Accelerators	electron, simulation, radiation, feedback	91
	V.Yu. Zaslavsky, N.S. Ginzburg, A. Malkin, N.Yu. Peskov, A. Sergeev IAP/RAS, Nizhny Novgorod, Russia A.V. Arzhannikov, E.S. Sandalov, S.L. Sinitsky, D.I. Skovorodin, A.A. Starostenko BINP SB RAS, Novosibirsk, Russia
	Funding: This work was supported by the Russian Scientific Foundation (RSCF), grant No. 19-12-00212. The paper is devoted to development of high-power long-pulse THz-band FELs based on new generation of linear induction accelerators which have been elaborated recently at Budker Institute (Novosibirsk). These accelerators generate microsecond electron beams with current at kA-level and energy of 2 to 5 MeV (with a possibility to increase electrons energy up to 20 MeV). Based on this beam, we initiated a new project of multi-MW long-pulse FEL operating in the frequency range of 1 to 10 THz using a wiggler period of 3 to 6 cm. For this FEL oscillator, we suggest a hybrid planar two-mirror resonator consisting of an upstream highly selective advanced Bragg reflector and a downstream weakly reflecting conventional Bragg reflector. Simulations demonstrate that the advanced Bragg reflector based on coupling of propagating and quasi-cutoff waves ensures the mode control at the values of the gap between the corrugated plates forming such resonator up to 20 wavelengths. Simulations of the FEL driven by electron beam generated by the LIU¿2 in the frame of both averaged approach and 3D PIC code demonstrate that the THz radiation power can reach the level of 10 to 20 MW.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-FEL2019-TUP021
About •	paper received ※ 28 August 2019 paper accepted ※ 28 August 2019 issue date ※ 05 November 2019
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TUP023	Analytical and Numerical Comparison of Different Approaches to the Description of SASE in High Gain FELs	radiation, simulation, undulator, bunching	94
	O.A. Shevchenko, N.A. Vinokurov BINP SB RAS, Novosibirsk, Russia N.A. Vinokurov NSU, Novosibirsk, Russia
	Correlation function theory which has been developed recently gives rigorous statistical description of the SASE FEL operation. It directly deals with the values averaged over many shots. There are two other approaches which are based either on Vlasov equation or on direct solution of particle motion equations. Both of them use random functions which relate to single shot. To check the validity of these three approaches it might be interesting to compare them with each other. In this paper we present the results of such comparison obtained for the 1-D FEL model. We show that two-particle correlation function approximation is equivalent to the quasilinear approximation of the Vlasov equation approach. These two approximations are in a good agreement with the results of direct solution of particle motion equations at linear and early saturation stages. To obtain this agreement at strong saturation high order harmonics in Vlasov equation have to be taken into account which corresponds to taking into account of three and more particle correlations in the correlation function approach.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-FEL2019-TUP023
About •	paper received ※ 19 August 2019 paper accepted ※ 25 August 2019 issue date ※ 05 November 2019
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TUP024	Electronic Modulation of the FEL-Oscillator Radiation Power Driven by ERL	radiation, electron, experiment, controls	98
	O.A. Shevchenko, E.V. Bykov, Ya.V. Getmanov, S.S. Serednyakov, S.V. Tararyshkin BINP SB RAS, Novosibirsk, Russia M.V. Fedin, A.R. Melnikov, S.L. Veber International Tomography Center, SB RAS, Novosibirsk, Russia Ya.V. Getmanov, S.S. Serednyakov NSU, Novosibirsk, Russia
	FEL oscillators usually operate in CW mode and produce periodic train of radiation pulses but some user experiments require modulation of radiation power. Conventional way to obtain this modulation is using of mechanical shutters but it cannot provide very short switching time and may lead to decreasing of the radiation beam quality. Another way could be based on the electron beam current modulation but it cannot be used in the ERL. We propose a simple way of fast control of the FEL lasing which is based on periodic phase shift of electron bunches with respect to radiation stored in optical cavity. The phase shift required to suppress lasing is relatively small and it does not change significantly repetition rate. This approach has been realized at NovoFEL facility. It allows to generate radiation macropulses of desirable length down to several microseconds (limited by quality factor of optical cavity and FEL gain) which can be synchronized with external trigger. We present detailed description of electronic power modulation scheme and discuss the results of experiments.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-FEL2019-TUP024
About •	paper received ※ 20 August 2019 paper accepted ※ 27 August 2019 issue date ※ 05 November 2019
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TUP025	Current Status of Free Electron Laser @ TARLA	electron, cryomodule, cavity, undulator	102
	A. Aksoy, Ö. Karslı, C. Kaya, İ.B. Koç Ankara University, Accelerator Technologies Institute, Golbasi, Turkey Ö.F. Elçim Ankara University Institute of Accelerator Technologies, Golbasi, Turkey
	Funding: Work supported by Strategy and Budget Department of Turkey with Grand No: 2006K120470 Turkish Accelerator and Radiation Laboratory (TARLA), which is supported by the Presidency Strategy and Budget Directorate of Turkey, aims to be the state of art research instrument for the radiation users from Turkey. Two superconducting accelerating modules of TARLA will drive two different planar undulator magnets with periods of 110 mm (U110) and 35 mm (U35) in order to generate high brightness Continuous Wave (CW) Free Electron Laser (FEL) tunable in between 5-350 µm. In addition, the linac will drive a Bremstrahlung radiation station to generate polarized gamma radiation. Main components of TARLA, such as injector, superconducting accelerating modules and cryoplant are under commissioning currently. In this study, we present current status of the facility in addition to expected FEL performance of the facility.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-FEL2019-TUP025
About •	paper received ※ 20 August 2019 paper accepted ※ 29 August 2019 issue date ※ 05 November 2019
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TUP026	Unaveraged Simulation of a Regenerative Amplifier Free Electron Laser	undulator, cavity, simulation, electron	106
	P. Pongchalee, B.W.J. MᶜNeil USTRAT/SUPA, Glasgow, United Kingdom B.W.J. MᶜNeil Cockcroft Institute, Warrington, Cheshire, United Kingdom
	A regenerative amplifier free-electron laser (RAFEL) design and simulation requires the modelling of both the electron-light interaction in the FEL undulator and the optical propagation within the cavity. An unaveraged 3D simulation was used to model the FEL interaction within the undulator using the Puffin code. This allows a broadband, high temporal-resolution of the FEL interaction. The Optical Propagation Code (OPC) was used to model the optical beam propagation within the cavity and diagnostics at the cavity mirrors. This paper presents the optical field conversion method between Puffin and the OPC codes and demonstrates the full model via a VUV-RAFEL simulation.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-FEL2019-TUP026
About •	paper received ※ 19 August 2019 paper accepted ※ 25 August 2019 issue date ※ 05 November 2019
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TUP027	Modelling Crystal Misaligments for the X-ray FEL Oscillator	cavity, alignment, undulator, simulation	110
	R.R. Lindberg ANL, Lemont, Illinois, USA
	Funding: Work supported by U.S. Dept. of Energy Office of Sciences under Contract No. DE-AC02-06CH11357. The X-ray FEL oscillator has the potential to be a revolutionary new light source providing unprecedented stability in a narrow bandwidth [1]. However, a detailed understanding of cavity tolerance and stability has only begun, and there are presently no suitable simulation tools. To address this issue, we have developed a fast FEL oscillator code that discretizes the field using a Gauss-Hermite mode expansion of the oscillator cavity. Errors in crystal alignment result in a mixing of the modes that is easily modeled with a loss and coupling matrix. We show first results from our code, including the effects of static and time-varying crystal misalignments. [1] K.-J. Kim, Y. Shvyd’ko, and S. Reiche, PRL 100 244802 (2008)
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-FEL2019-TUP027
About •	paper received ※ 20 August 2019 paper accepted ※ 25 August 2019 issue date ※ 05 November 2019
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TUP028	Power Variations of an X-ray FEL Oscillator in Saturation	electron, simulation, cavity, undulator	114
	R.R. Lindberg, K. Kim ANL, Lemont, Illinois, USA
	Funding: Work supported by U.S. Dept. of Energy Office of Sciences under Contract No. DE-AC02-06CH11357. Basic FEL theory predicts that the fractional power fluctuations of an ideal oscillator in steady state should be given by the ratio of the spontaneous power in the oscillator bandwidth to that stored in the cavity at saturation. For the X-ray FEL oscillator with its narrow bandwidth Bragg crystal mirrors, this ratio is typically a few parts per million, but some simulations have shown evidence of power oscillations on the percent level. We show that this is not related to the well-known sideband instability, but rather is purely numerical and can be eliminated by changing the particle loading. We then briefly discuss to what extent variations in electron beam arrival time may degrade the power stability.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-FEL2019-TUP028
About •	paper received ※ 20 August 2019 paper accepted ※ 25 August 2019 issue date ※ 05 November 2019
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TUP032	Regenerative Amplification for a Hard X-Ray Free-Electron Laser	cavity, electron, radiation, undulator	118
	G. Marcus, Y. Ding, Y. Feng, A. Halavanau, Z. Huang, J. Krzywiński, J.P. MacArthur, R.A. Margraf, T.O. Raubenheimer, D. Zhu SLAC, Menlo Park, California, USA V. Fiadonu Santa Clara University, Santa Clara, California, USA
	Funding: This work was supported by the Department of Energy, Laboratory Directed Research and Development program at SLAC National Accelerator Laboratory, under contract DE-AC02-76SF00515. An X-ray regenerative amplifier FEL (XRAFEL) utilizes an X-ray crystal cavity to provide optical feedback to the entrance of a high-gain undulator. An XRAFEL system leverages gain-guiding in the undulator to reduce the cavity alignment tolerances and targets the production of longitudinally coherent and high peak power and brightness X-ray pulses that could significantly enhance the performance of a standard single-pass SASE amplifier. The successful implementation of an X-ray cavity in the XRAFEL scheme requires the demonstration of X-ray optical components that can either satisfy large output coupling constraints or passively output a large fraction of the amplified coherent radiation. Here, we present new schemes to either actively Q-switch a diamond Bragg crystal through lattice constant manipulation or passively output couple a large fraction of the stored cavity radiation through controlled FEL microbunch rotation. A beamline design study, cavity stability analysis, and optimization will be presented illustrating the performance of potential XRAFEL configurations at LCLS-II/-HE using high-fidelity simulations.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-FEL2019-TUP032
About •	paper received ※ 24 August 2019 paper accepted ※ 26 August 2019 issue date ※ 05 November 2019
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TUP033	Q-Switching of X-Ray Optical Cavities by Using Boron Doped Buried Layer Under a Surface of a Diamond Crystal	laser, cavity, electron, free-electron-laser	122
	J. Krzywiński, Y. Feng, A. Halavanau, Z. Huang, A.M. Kiss, J.P. MacArthur, G. Marcus, T. Sato, D. Zhu SLAC, Menlo Park, California, USA
	Improvement of the longitudinal coherence of X-ray Free Electron Lasers has been the subject of many recent investigations. The XFEL oscillator (XFELO) and Regenerative Amplifier Free-Electron Laser (RAFEL) schemes offer a pathway to fully coherent, high brightness X-ray radiation. The XFELO and RAFEL consist of a high repetition rate electron beam, an undulator and an X-ray crystal cavity to provide optical feedback. The X-ray cavity will be based on diamond crystals in order to manage a high thermal load. We are investigating a ’Q switching’ mechanism that involves the use of a ’Bragg switch’ to dump the X-ray pulse energy built-up inside an X-ray cavity. In particular, one can use an optical laser to manipulate the diamond crystal lattice constant to control the crystal reflectivity and transmission. It has been shown that a 9 MeV focused boron beam can create a buried layer, approximately 5 microns below surface, with a boron concentration up to 10²¹ atoms/cm³. Here, we present simulations showing that absorbing laser pulses by a buried layer under the crystal surface would allow creating a transient temperature profile which would be well suited for the ’Q switching’ scheme.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-FEL2019-TUP033
About •	paper received ※ 21 August 2019 paper accepted ※ 29 August 2019 issue date ※ 05 November 2019
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TUP036	A Waveguide-Based High Efficiency Super-Radiant FEL Operating in the THz Regime	GUI, radiation, electron, undulator	127
	P. Musumeci, A.C. Fisher UCLA, Los Angeles, California, USA A. Gover University of Tel-Aviv, Faculty of Engineering, Tel-Aviv, Israel E.A. Nanni, E.J. Snively SLAC, Menlo Park, California, USA S.B. van der Geer Pulsar Physics, Eindhoven, The Netherlands
	Funding: DOE grant No. DE-SC0009914 and NSF grant PHY-1734215 In this paper we describe a novel self-consistent 3D simulation approach for a waveguide FEL operating in the zero-slippage regime to generate high power THz radiation. In this interaction regime, the phase and group velocity of the radiation are matched to the relativistic beam traveling in the undulator achieving long interaction lengths. Our numerical approach is based on expanding the existing 3D particle tracking code GPT (General Particle Tracer) to follow the interaction of the particles in the beam with the electromagnetic field modes of the waveguide. We present two separate studies: one for a case which was benchmarked with experimental results and another one for a test case where, using a longer undulator and larger bunch charge, a sizable fraction of the input beam energy can be extracted and converted to THz radiation. The model presented here is an important step in the development of the zero-slippage FEL scheme as a source for high average and peak power THz radiation.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-FEL2019-TUP036
About •	paper received ※ 20 August 2019 paper accepted ※ 29 August 2019 issue date ※ 05 November 2019
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TUP038	Axial Symmetry in Spontaneous Undulator Radiation for XFELO Two-Bunch Experiment	electron, experiment, laser, radiation	134
	Y.S. Li University of Chicago, Chicago, Illinois, USA K. Kim, R.R. Lindberg ANL, Lemont, Illinois, USA
	Funding: U.S. DOE, Office of Science, Office of BES, under Contract No. DE-AC02-06CH11357 and National Science Foundation under Award No. PHY-1549132, the Center for Bright Beams. A well known discrepancy exists between 2D and 3D FEL simulation codes with respect to the radiation field intensity prior to the exponential gain regime [1]. This can be qualitatively explained by the fact that the 3D field representation preserves many more modes than does the axisymmetric field solved for by a 2D code. In this paper, we seek to develop an analytical model that quantifies this difference. We begin by expanding the spontaneous undulator radiation field as a multipole series, whose lowest order mode is axisymmetric. This allows us to calculate the difference in predicted intensity. Next, we confirm these results with numerical calculation and existing FEL codes GINGER and GENESIS. Finally, we discuss the implications of this study with respect to the XFELO two-bunch experiment to be conducted at LCLS-II. [1] Z. Huang and K.-J. Kim, "Review of X-ray free-electron laser theory", Phys. Rev. ST-AB, vol. 10, p. 034801, 2007.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-FEL2019-TUP038
About •	paper received ※ 19 August 2019 paper accepted ※ 28 August 2019 issue date ※ 05 November 2019
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TUP041	X-cos SCILAB Model for Simulation of Intensity and Gain of Planar Undulator Radiation	undulator, simulation, electron, radiation	138
	H. Jeevakhan NITTTR, Bhopal, India G. Mishra Devi Ahilya University, Indore, India
	SCILAB X-cos based model has been designed to simulate the Intensity and Gain of planar undulator radiation. Numerical approach has been used to determine the trajectories of an electron along x and z direction, traversing through a planar undulator. The present paper describes the technical details of the different blocks, parameters and possibility of combined model used for trajectory and intensity simulation Results are compared with the previous conventional syntax based codes.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-FEL2019-TUP041
About •	paper received ※ 01 August 2019 paper accepted ※ 27 August 2019 issue date ※ 05 November 2019
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TUP042	Analysis of Undulator Radiations With Asymmetric Beam and Non-Periodic Magnetic Field	undulator, electron, radiation, resonance	141
	H. Jeevakhan NITTTR, Bhopal, India G. Mishra Devi Ahilya University, Indore, India
	Harmonic Undulator radiations at third harmonics with non periodic constant magnetic field has been analysed. Symmetric and asymmetric electron beam with homogeneous spread has been used to present viable solution for the resonance shift inherited in undulator with constant magnetic field. The radiation recovers shifts in resonance and regain its intensity with asymmetric electron beam and harmonic field Harmonic undulator, energy spread
	Poster TUP042 [2.886 MB]
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-FEL2019-TUP042
About •	paper received ※ 01 August 2019 paper accepted ※ 31 October 2019 issue date ※ 05 November 2019
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TUP047	An Analysis of Optimal Initial Detuning for Maximum Energy-Extraction Efficiency	electron, extraction, synchrotron, undulator	145
	Q.K. Jia USTC/NSRL, Hefei, Anhui, People’s Republic of China
	For low gain free electron laser (FEL), the phase space evolutions of trapped electrons in the phase bucket are analyzed through calculating their synchrotron oscillation periods, which vary with the initial detuning and initial phase. The optimal initial detuning for the maximum energy-extraction efficiency and the corresponding saturation length are given. The analysis demonstrated that for the low gain case the gain of the strong optical field is about a quarter of that of the weak optical field (small signal gain), and the saturation power larger than that of high gain FEL can be achieved in the resonator of oscillator FEL.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-FEL2019-TUP047
About •	paper received ※ 19 August 2019 paper accepted ※ 27 August 2019 issue date ※ 05 November 2019
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TUP049	Simulating Shot-Noise of ’Real’ Electron Bunches	micro-particles, electron, simulation, bunching	149
	P. Traczykowski, L.T. Campbell, B.W.J. MᶜNeil USTRAT/SUPA, Glasgow, United Kingdom L.T. Campbell, B.W.J. MᶜNeil, P. Traczykowski Cockcroft Institute, Warrington, Cheshire, United Kingdom L.T. Campbell, P. Traczykowski STFC/DL/ASTeC, Daresbury, Warrington, Cheshire, United Kingdom
	An algorithm and numerical code for the up-sampling of a system of particles, from a smaller to a larger number, is described. The method introduces a Poissonian ’shot-noise’ to the up-sampled distribution [1], typical of the noise statistics arising in a bunch of particles generated by a particle accelerator. The algorithm is applied on a phase-space distribution of relatively few simulation particles representing an electron beam generated by particle accelerator modelling software, for subsequent injection into an Free Electron Laser (FEL) amplifier which is used here to describe the model. A much larger number of particles is usually required to model the FEL lasing process than is required in the simulation models of the electron beam accelerators that drive it. A numerical code developed from the algorithm was then used to generate electron bunches for injection into to an unaveraged 3D FEL simulation code, Puffin [2]. Results show good qualitative and quantitative agreement with analytical theory. The program and usage manual is available to download from GitHub [3]. [1] B.W.J. McNeil, M.W. Poole and G.R.M. Robb, Physical Review Special Topics - Accelerators and Beams Vol 6, 070701 (2003). [2] L.T. Campbell and B.W.J. McNeil, Phys. Plasmas 19, 093119 (2012). [3] https://github.com/UKFELs/JDF
	Poster TUP049 [1.419 MB]
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-FEL2019-TUP049
About •	paper received ※ 20 August 2019 paper accepted ※ 27 August 2019 issue date ※ 05 November 2019
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TUP050	Comparison Between, and Validation Against an Experiment of, a Slowly-varying Envelope Approximation Code and a Particle-in-Cell Simulation Code for Free-Electron Lasers	undulator, simulation, experiment, electron	153
	P. Traczykowski, L.T. Campbell, J. Henderson, B.W.J. MᶜNeil USTRAT/SUPA, Glasgow, United Kingdom L.T. Campbell, J. Henderson, P. Traczykowski STFC/DL/ASTeC, Daresbury, Warrington, Cheshire, United Kingdom H. Freund University of New Mexico, Albuquerque, USA B.W.J. MᶜNeil, P. Traczykowski Cockcroft Institute, Warrington, Cheshire, United Kingdom P.J.M. van der Slot Mesa+, Enschede, The Netherlands
	Free-electron laser simulation codes employ either the Slowly-Varying Envelope Approximation (SVEA) or a Particle-in-Cell (PiC) formulation. Maxwell’s equations are averaged over the fast time scale in the SVEA so that there is no need to resolve the wave period. In contrast, the fast oscillation is retained in PiC codes. As a result, the SVEA codes are much less computationally intensive and are used more frequently than PiC codes. While the orbit dynamics in PiC codes and some SVEA Codes (MEDUSA and MINERVA) use the full unaveraged Lorentz force equations, some SVEA codes use the Kroll-Morton-Rosenbluth (KMR) approximation (GENESIS, GINGER, FAST, and TDA3D). Steady-state simulation comparisons [1] have appeared in the literature between different codes using the averaged and unaveraged particle dynamics. Recently, a comparison between three KMR SVEA codes (GENESIS, GINGER, and FAST) and the PUFFIN PiC code in the time-dependent regime has been reported [2]. In this paper, we present a comparison between the unaveraged PiC code PUFFIN, the unaveraged SVEA code MINERVA for the time-dependent simulation of SASE free-electron lasers with the experimental measurements from SPARC SASE FEL at ENEA Frascati. [1] S.G. Biedron et al., NIMA 445, 110 (2000). [2] B. Garcia et al., paper presented at the 38th International Free Electron Laser Conference, Santa Fe, New Mexico, 20 - 25 August 2017.
	Poster TUP050 [0.908 MB]
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-FEL2019-TUP050
About •	paper received ※ 02 August 2019 paper accepted ※ 28 August 2019 issue date ※ 05 November 2019
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TUP051	Plasma Accelerator Driven Coherent Spontaneous Emission	electron, radiation, bunching, undulator	157
	B.M. Alotaibi, R. Altuijri PNU, Riyadh, Kingdom of Saudi Arabia B.M. Alotaibi, R. Altuijri, A.F. Habib, B. Hidding, B.W.J. MᶜNeil, P. Traczykowski USTRAT/SUPA, Glasgow, United Kingdom A.F. Habib, B. Hidding, B.W.J. MᶜNeil, P. Traczykowski Cockcroft Institute, Warrington, Cheshire, United Kingdom
	Plasma accelerators [1] are a potentially important source of high energy, low emittance electron beams with high peak currents generated within a relatively short distance. As such, they may have an important application in the driving of coherent light sources such as the Free Electron Laser (FEL) which operate into the X-ray region [2]. While novel plasma photocathodes [3] may offer orders of magnitude improvement to the normalized emittance and brightness of electron beams compared to Radio Frequency-driven accelerators, a substantial challenge is the energy spread and chirp of beams, which can make FEL operation impossible. In this paper it is shown that such an energy-chirped, ultrahigh brightness electron beam, with dynamically evolving current profile due to ballistic bunching at moderate energies, can generate significant coherent radiation output via the process of Coherent Spontaneous Emission (CSE)[4]. While this CSE is seen to cause some FEL-induced electron bunching at the radiation wavelength, the dynamic evolution of the energy chirped pulse dampens out any high-gain FEL interaction. [1] E. Esary et al., Reviews of Modern Physics p. 1229 (2009). [2] B. W. J. McNeil and N. R. Thompson, 2010 Nat. Photon.4 814-21 [3] B. Hidding et al., 2012 Phys. Rev. Lett. 108 035001 [4] L. T. Campbell and B. W. J. McNeil, 2012, in Proc. FEL2012
	Poster TUP051 [1.401 MB]
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-FEL2019-TUP051
About •	paper received ※ 20 August 2019 paper accepted ※ 27 August 2019 issue date ※ 05 November 2019
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TUP053	An Investigation of Possible Non-Standard Photon Statistics in a Free-Electron Laser I: Experiment	photon, experiment, cavity, radiation	161
	J.-W. Park University of Hawaii, Honolulu,, USA K.-J. Kim, R.R. Lindberg ANL, Lemont, Illinois, USA
	Funding: Work supported by U.S. DOE, Office of Science, Office of BES, under Award No. DE-SC0018428. It was reported that the photon statistics of the seventh coherent spontaneous harmonic radiation of the MARK III FEL was sub-Poissonian [1], which concludes that Fano factor F (the ratio of photon number variance to the average photon number) is less than unity. Whether FEL light exhibits such non-standard behavior is an important issue; if it does, our understanding of the FEL needs to be radically modified. In this paper, we re-examine the analyses of experimental data in Ref. [1]. We find that the observed value of F could be explained within the standard FEL theory if one combines the detector dead time effect with photon clustering arising from the FEL gain. We propose an improved experiment for a more definitive measurement of the FEL photon statistics. [1] T. Chen and J.M. Madey, J. Phys. Rev. Lett. 86, 5906 (2001).
	Poster TUP053 [0.929 MB]
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-FEL2019-TUP053
About •	paper received ※ 21 August 2019 paper accepted ※ 12 September 2019 issue date ※ 05 November 2019
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TUP054	An Investigation of Possible Non-Standard Photon Statistics in a Free-Electron Laser II: Theory	electron, photon, radiation, laser	165
	J.-W. Park University of Hawaii, Honolulu,, USA K.-J. Kim, R.R. Lindberg ANL, Lemont, Illinois, USA K.-J. Kim University of Chicago, Chicago, Illinois, USA
	Funding: Work supported by U.S. DOE, Office of Science, Office of BES, under Award No. DE-SC0018428. In this paper we explore whether we can at present find a theoretical basis for non-standard, sub-Poissonian photon statistics in the coherent spontaneous harmonic radiation of an FEL as was claimed to have been measured with the Mark III FEL [1]. We develop a one dimensional quantum FEL oscillator model of the harmonic radiation in the linear gain regime to calculate the photon statistics. According to our study, it seems unlikely that the photon statistics for an FEL oscillator starting from the noise could be sub-Poissonian. [1] T. Chen and J.M. Madey, J. Phys. Rev. Lett. 86, 5906 (2001).
	Poster TUP054 [0.386 MB]
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-FEL2019-TUP054
About •	paper received ※ 21 August 2019 paper accepted ※ 16 September 2019 issue date ※ 05 November 2019
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TUP055	Two-Color Operation of FLASH2 Undulator	undulator, electron, laser, operation	168
	E. Schneidmiller, M. Braune, B. Faatz, U. Jastrow, M. Kuhlmann, A.A. Sorokin, K.I. Tiedtke, M.V. Yurkov DESY, Hamburg, Germany
	FLASH is the first soft X-ray FEL user facility, routinely providing brilliant photon beams for users since 2005. The second undulator branch of this facility, FLASH2, is gap-tunable which allows to test and use advanced lasing concepts. In particular, we tested recently a two-color mode of operation based on the alternation of tunes of the undulator segments (every other segment is tuned to the second wavelength). This scheme is advantageous in comparison with a subsequent generation of two colors in two different parts of the undulator. First, source positions of two FEL beams are close to each other which makes it easier to handle them. Second, the amplification is more efficient in this configuration since the segments with respectively "wrong" wavelength act as bunchers. We developed methods for online intensity measurements of the two colors simultaneously that require a combination of two detectors. We present some examples of such measurements in the XUV and soft X-ray regimes.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-FEL2019-TUP055
About •	paper received ※ 20 August 2019 paper accepted ※ 28 August 2019 issue date ※ 05 November 2019
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TUP056	Feasibility Studies of the 100 keV Undulator Line of the European XFEL	undulator, electron, photon, laser	172
	E. Schneidmiller, V. Balandin, W. Decking, M. Dohlus, N. Golubeva, D. Nölle, M.V. Yurkov, I. Zagorodnov DESY, Hamburg, Germany G. Geloni, Y. Li, S. Molodtsov, J. Pflüger, S. Serkez, H. Sinn, T. Tanikawa, S. Tomin EuXFEL, Schenefeld, Germany
	The European XFEL is a multi-user X-ray FEL facility based on superconducting linear accelerator. Presently, three undulators (SASE1, SASE2, SASE3) deliver high-brightness soft- and hard- X-ray beams for users. There are two empty undulator tunnels that were originally designed to operate with spontaneous radiators. We consider instead a possible installation of two FEL undulators. One of them (SASE4) is proposed for the operation in ultrahard X-ray regime, up to the photon energy of 100 keV. In this contribution we present the results of the first feasibility studies of this option.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-FEL2019-TUP056
About •	paper received ※ 20 August 2019 paper accepted ※ 27 August 2019 issue date ※ 05 November 2019
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TUP057	Analysis of Parameter Space of Soft X-Ray Free Electron Laser at the European XFEL Driven by High and Low Energy Electron Beam	undulator, electron, radiation, operation	176
	E. Schneidmiller, M.V. Yurkov DESY, Hamburg, Germany
	Three undulator beamlines: SASE1 and SASE2 (hard X-ray), and SASE3 (soft X-ray) are in operation at the European XFEL serving six user instruments. Next stages of the facility development are installation of two undulator beamlines in empty tunnels SASE4 and SASE5 as medium term upgrade, and extension of the facility with the second fan of undulators as long term upgrade. Construction of soft X-ray beamlines is considered in both upgrade scenario. In the case of SASE4/SASE5 electron beam with energies 8.5 GeV - 17.5 GeV will be used in order to provide simultaneous operation of new undulator beamlines with existing SASE1-SASE3. One of the scenarios for a second fan of undulators involves using of low energy (2.5 GeV) electron beam. In this paper we analyze parameter space of soft X-ray SASE FELs driven by high energy and low energy electron beam, compare output characteristics, and discuss potential advantages and disadvantages.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-FEL2019-TUP057
About •	paper received ※ 20 August 2019 paper accepted ※ 27 August 2019 issue date ※ 05 November 2019
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TUP058	First Characterization of the Photon Beam at the European XFEL in July, 2017	radiation, photon, electron, undulator	180
	V. Balandin, B. Beutner, F. Brinker, W. Decking, M. Dohlus, L. Fröhlich, U. Jastrow, R. Kammering, T. Limberg, D. Nölle, M. Scholz, A.A. Sorokin, K.I. Tiedtke, M.V. Yurkov, I. Zagorodnov DESY, Hamburg, Germany U. Boesenberg, W. Freund, J. Grünert, A. Koch, N.G. Kujala, J. Liu, Th. Maltezopoulos, M. Messerschmidt, I. Petrov, L. Samoylova, H. Sinn EuXFEL, Schenefeld, Germany
	North branch of the European XFEL, SASE1, produced first light on May 3rd, 2017, and XFEL operation has been gradually improved then. First characterization of the photon beam has been performed in July / August 2017, just before an official starting date of user experiments (September 1st, 2017). Energy of the electron beam was 14 GeV, bunch charge was 500 pC, photon energy was 9.3 keV. With photon diagnostics available at that time (X-ray gas monitor (XGM) and FEL imager) we measured the gain curve and traced evolution of the FEL radiation mode along the undulator. An important conclusion is that experimental results demonstrate reasonable agreement with baseline parameters. Developed techniques of the photon beam characterization also provided solid base for identification of the problems and means for improving SASE FEL tuning and operation.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-FEL2019-TUP058
About •	paper received ※ 20 August 2019 paper accepted ※ 27 August 2019 issue date ※ 05 November 2019
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TUP059	Influence of Energy Chirp in the Electron Beam and Undulator Tapering on Spatial Properties of the Radiation From Seeded and SASE FEL	undulator, radiation, electron, laser	184
	E. Schneidmiller, M.V. Yurkov DESY, Hamburg, Germany
	Energy chirp and undulator tapering change resonance condition along the electron beam and undulator which results in modification of the radiation amplification process. Well known examples are post-saturation undulator tapering for radiation power increase, reverse undulator tapering for effective operation of afterburners, and application of linear undulator tapering for compensation of energy chirp effect. These are essentially one dimensional effects. In addition, energy chirp and undulator tapering also change spatial properties of the radiation which can be important for the users of X-ray FEL facilities. In this report we present detailed analysis of the spatial properties of the radiation from an FEL amplifier with tapered undulator and chirped electron beam. Two configurations, seeded FEL amplifier, and SASE FEL are under consideration. Dependence of the spatial distributions on the electron beam properties is studied, and their evolution along the undulator is traced. It is shown that spatial properties of the radiation may be significantly distorted by the effects of energy chirp in the electron beam and undulator tapering.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-FEL2019-TUP059
About •	paper received ※ 24 August 2019 paper accepted ※ 28 August 2019 issue date ※ 05 November 2019
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TUP060	An Advanced Compression Option for the European XFEL	electron, undulator, laser, photon	187
	I. Zagorodnov, M. Dohlus, E. Schneidmiller, M.V. Yurkov DESY, Hamburg, Germany
	An advanced compression scheme which allows to obtain a high peak current while preserving the low slice emittance is considered. The beam is compressed weakly in the bunch compressors and the current is increased by eSASE setup at the entrance of the undulator line. It is shown by numerical studies that such approach allows to reduce harmful collective effects in the bunch compressors and in the transport line. Simulations of FEL physics confirm the possibility to obtain a high level of SASE radiation at the ultra-hard photon energy level of 100 keV.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-FEL2019-TUP060
About •	paper received ※ 19 August 2019 paper accepted ※ 25 August 2019 issue date ※ 05 November 2019
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TUP061	Super-X: Simulations for Extremely Hard X-Ray Generation With Short Period Superconducting Undulators for the European XFEL	undulator, electron, photon, simulation	191
	S. Serkez, G. Geloni, S. Karabekyan, Y. Li, T. Tanikawa, S. Tomin, F. Wolff-Fabris EuXFEL, Schenefeld, Germany C. Boffo Bilfinger Noell GmbH, Wuerzburg, Germany S. Casalbuoni KIT, Eggenstein-Leopoldshafen, Germany M. Dohlus, E. Schneidmiller, M.V. Yurkov, I. Zagorodnov DESY, Hamburg, Germany A. Trebushinin BINP, Novosibirsk, Russia
	The European XFEL is a high-repetition multi-user facility with nominal photon energy range covering almost 3 orders of magnitude: 250 eV - 25 keV. In this work we explore the possibility to extend the photon energy range of the facility up to 100 keV via combination of superconducting undulator technology, period doubling and harmonic lasing, thus allowing for excellent tunability. To this purpose, we propose a dedicated FEL line, discuss its overall concept and provide analytical and numerical estimations of its expected performance.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-FEL2019-TUP061
About •	paper received ※ 20 August 2019 paper accepted ※ 25 August 2019 issue date ※ 05 November 2019
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TUP062	Two Colors at the SASE3 Line of the European XFEL: Project Scope and First Measurements	electron, photon, experiment, radiation	195
	S. Serkez, G. Geloni, N. Gerasimova, J. Grünert, S. Karabekyan, A. Koch, J. Laksman, Th. Maltezopoulos, T. Mazza, M. Meyer, S. Tomin EuXFEL, Schenefeld, Germany W. Decking, L. Fröhlich, V. Kocharyan, Y.A. Kot, E. Saldin, E. Schneidmiller, M. Scholz, M.V. Yurkov, I. Zagorodnov DESY, Hamburg, Germany M. Huttula University of Oulu, Oulu, Finland E. Kukk University of Turku, Turku, Finland
	The European XFEL is a high-repetition rate facility that generates high-power SASE radiation pulses in three beamlines. A joint upgrade project, with Finnish universities, to equip the SASE3 beamline with a chicane has been recently approved to generate two SASE pulses with different photon energies and temporal separation. In this work we report the status of the project, its expected performance, and recent experimental results. Additionally, we discuss methods to diagnose the properties of the generated radiation.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-FEL2019-TUP062
About •	paper received ※ 20 August 2019 paper accepted ※ 29 August 2019 issue date ※ 05 November 2019
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TUP063	Physical Design and FEL Performance Study for FEL-III Beamline of SHINE	undulator, wakefield, photon, electron	199
	N. Huang SINAP, Shanghai, People’s Republic of China H.X. Deng, B. Liu, D. Wang SARI-CAS, Pudong, Shanghai, People’s Republic of China
	The first hard X-ray free electron laser (XFEL) facility in China, the Shanghai High-Repetition-Rate XFEL and Extreme Light Facility (SHINE), is under construction, which allows for generating X-ray pulses in the photon energy range from 3 keV to 25 keV. To produce X-ray pulses with photon energy up to 25 keV, FEL-III undulator line of SHINE employs superconducting undulators. However, the smaller gap of the superconducting undulator poses serious wakefield effect reducing the FEL power, compared to the normal planar undulator. For a setup design optimization, the design and performance of the FEL-III undulator line are presented using start-to-end beam simulations at self-amplified spontaneous emission (SASE) and self-seeding mode. The wakefield impact on FEL performance is then investigated. A linear undulator tapering technique is adopted for recovering the FEL power to the non-wakefield level.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-FEL2019-TUP063
About •	paper received ※ 19 August 2019 paper accepted ※ 28 August 2019 issue date ※ 05 November 2019
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TUP064	Effect on FEL Gain Curve Using Phase Shifters	electron, undulator, laser, simulation	203
	M.H. Cho, H.-S. Kang, G. Kim, C.H. Shim, H. Yang PAL, Pohang, Republic of Korea
	Phase matching between FEL and electron beam should be precisely controlled for FEL amplification. Phase shifters located between undulators performs the phase matching. An electron beam can be controlled to be in the in- or out-phase by setting the phase shifters from the phase shifter scan. In this article, we show effects of FEL gain curve by setting the in- and out-phase of electron beam. We address reasons of the reduction of FEL intensity in the out-phase condition dividing the linear and saturation FEL amplification regimes. In the linear regime the gain curve is shifted, and in the saturation regime the electron loss occurs during the undulator tapering. Our results show agreements with experiments performed at PAL-XFEL.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-FEL2019-TUP064
About •	paper received ※ 21 August 2019 paper accepted ※ 28 August 2019 issue date ※ 05 November 2019
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TUP065	Optimization of a Coherent Undulator Beamline for New Advanced Synchrotron Light Source in Korea	undulator, electron, synchrotron, radiation	206
	I.G. Jeong, P. Buaphad, Y.J. Joo, Y. Kim, H.R. Lee University of Science and Technology of Korea (UST), Daejeon, Republic of Korea P. Buaphad, Y.J. Joo, Y. Kim, H.R. Lee KAERI, Jeongeup-si, Republic of Korea M.Y. Han, I.G. Jeong, J.Y. Lee, S.H. Lee Korea Atomic Energy Research Institute (KAERI), Daejeon, Republic of Korea
	Recently, the demand for a new advanced synchrotron light source in Korea is rapidly growing. Six local governments in Korea would like to host the new synchrotron light source project in their own provinces. The new advanced synchrotron light source will be the Diffraction-Limited Storage Ring (DLSR), which is based on the Multi-Bend Achromat (MBA) lattice. For the new synchrotron light source, we would like to build a special 60-m long coherent undulator beamline, which can deliver high-intensity coherent radiation at the hard X-ray region. To design the coherent undulator beamline, we have performed numerous beam dynamics simulations with GENESIS and SIMPLEX codes. In this paper, we report design concepts and those simulation results for the coherent undulator beamline.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-FEL2019-TUP065
About •	paper received ※ 26 August 2019 paper accepted ※ 26 August 2019 issue date ※ 05 November 2019
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TUP066	Start-to-End Simulations for the Soft X-Ray FEL at the MAX IV Laboratory	simulation, electron, linac, undulator	210
	W. Qin, J. Andersson, F. Curbis, L. Isaksson, M. Kotur, E. Mansten, M.A. Pop, S. Thorin, S. Werin MAX IV Laboratory, Lund University, Lund, Sweden F. Curbis, S. Werin SLF, Lund, Sweden
	Funding: The work is supported by Knut and Alice Wallenberg foundation. A Soft X-ray FEL (the SXL) using the existing 3 GeV linac at the MAX IV Laboratory is currently in the design phase. In this contribution, start-to-end simulations, including the photo-injector simulations using ASTRA, the linac simulations using ELEGANT and the FEL simulations using GENESIS, are presented for 100 pC and 10 pC operation modes. The features of the electron beam from the MAX IV linac and their impact on the FEL performance are discussed.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-FEL2019-TUP066
About •	paper received ※ 20 August 2019 paper accepted ※ 28 August 2019 issue date ※ 05 November 2019
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TUP067	Advanced Concepts in the Design for the Soft X-Ray FEL at MAX IV	undulator, electron, laser, brightness	214
	W. Qin, F. Curbis, M.A. Pop, S. Werin MAX IV Laboratory, Lund University, Lund, Sweden F. Curbis, S. Werin SLF, Lund, Sweden
	Funding: The work is supported by Knut and Alice Wallenberg foundation. A Soft X-ray FEL (the SXL) is currently being designed at the MAX IV Laboratory. In the work to adapt the FEL to the scientific cases several advanced options are being studied for coherence enhancement, generation of short pulses and two-color pulses. We will discuss the current status and the schemes studied, especially regarding the FEL performance with the features of the MAX IV linac, including a positive energy chirp.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-FEL2019-TUP067
About •	paper received ※ 20 August 2019 paper accepted ※ 29 August 2019 issue date ※ 05 November 2019
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TUP072	Orbital Angular Momentum from SASE	electron, quadrupole, radiation, undulator	218
	J.F. Morgan, B.W.J. MᶜNeil USTRAT/SUPA, Glasgow, United Kingdom B.W.J. MᶜNeil, J.F. Morgan, B.D. Muratori, P.H. Williams, A. Wolski Cockcroft Institute, Warrington, Cheshire, United Kingdom B.D. Muratori, P.H. Williams STFC/DL/ASTeC, Daresbury, Warrington, Cheshire, United Kingdom A. Wolski The University of Liverpool, Liverpool, United Kingdom
	Radiation with orbital angular momentum, OAM, has many applications such as in imaging systems and microscopic tweezers [1]. The feasibility of generating light with OAM in a free electron laser, FEL, from amplified shot noise in an electron beam is investigated using the FEL simulation code Puffin [2]. This may allow generation of OAM radiation at shorter wavelengths than currently available, as well as the opportunity to incorporate the technique with other SASE manipulation schemes such as mode locking [3]. [1] A. M. Yao and M. J. Padgett, Adv. Opt. Photon. 3, 161(2011) [2] L. T. Campbell and B. W. J. McNeil, Phys. Plasmas. 19, 093119(2012) [3] D. J. Dunning, B. W. J. McNeil, and N. R. Thompson, Phys. Rev. Lett. 110, 104801(2013)
	Poster TUP072 [1.311 MB]
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-FEL2019-TUP072
About •	paper received ※ 20 August 2019 paper accepted ※ 28 August 2019 issue date ※ 05 November 2019
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TUP073	High-Repetition-Rate Seeding Schemes Using a Resonator-Amplifier Setup	laser, electron, radiation, cavity	222
	S. Ackermann, B. Faatz, V. Grattoni, C. Lechner, G. Paraskaki DESY, Hamburg, Germany G. Geloni, S. Serkez, T. Tanikawa EuXFEL, Schenefeld, Germany W. Hillert University of Hamburg, Institut für Experimentalphysik, Hamburg, Germany
	The spectral and temporal properties of Free-Electron Lasers (FEL) operating on the basis of self-amplified spontaneous emission (SASE) suffer from the stochastic behavior of the start-up process. Several so-called "seeding"-techniques using external radiation fields to overcome this limitation have been proposed and demonstrated. The external seed is usually generated by demanding, high-power laser systems, which are not available with a sufficient laser pulse energy at the high repetition rates of superconducting FEL facilities. In this contribution we discuss several seeding schemes that lower the requirements for the used laser systems, enabling seeded operation at high repetition rates by the means of a resonator-amplifier setup.
	Poster TUP073 [0.521 MB]
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-FEL2019-TUP073
About •	paper received ※ 06 August 2019 paper accepted ※ 29 August 2019 issue date ※ 05 November 2019
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TUP074	FLASH Upgrade for Seeding	laser, undulator, simulation, electron	226
	V. Grattoni, S. Ackermann, B. Faatz, T. Lang, C. Lechner, M.M. Mohammad Kazemi, G. Paraskaki DESY, Hamburg, Germany W. Hillert University of Hamburg, Institut für Experimentalphysik, Hamburg, Germany
	An upgrade for FLASH, the SASE FEL in Hamburg, is planned after 2020 aiming at fulfilling user requirements like fully coherent, variable polarization, and multi-colour pulses. In this proceeding, we focus on the FLASH1 beamline that will be operated in seeded mode at a high repetition rate. In particular, we will present and discuss the proposed seeding schemes for delivering FEL radiation with wavelengths from 60 down to 4 nm
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-FEL2019-TUP074
About •	paper received ※ 19 August 2019 paper accepted ※ 28 August 2019 issue date ※ 05 November 2019
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TUP076	Seeding R&D at sFLASH	electron, laser, free-electron-laser, experiment	230
	C. Lechner, S. Ackermann, R.W. Aßmann, B. Faatz, V. Grattoni, I. Hartl, S.D. Hartwell, R. Ivanov, T. Laarmann, T. Lang, M.M. Mohammad Kazemi, G. Paraskaki, A. Przystawik, J. Zheng DESY, Hamburg, Germany A. Azima, H. Biss, M. Drescher, W. Hillert, V. Miltchev, J. Roßbach University of Hamburg, Institut für Experimentalphysik, Hamburg, Germany S. Khan DELTA, Dortmund, Germany
	Funding: Work supported by Federal Ministry of Education and Research of Germany under contract No. 05K13GU4, 05K13PE3, and 05K16PEA. Free-electron lasers (FELs) based on the self-amplified spontaneous emission (SASE) principle generate photon pulses with typically poor longitudinal coherence. FEL seeding techniques greatly improve longitudinal coherence by initiating FEL amplification in a controlled way using coherent light pulses. The sFLASH experiment installed at the FEL user facility FLASH at DESY in Hamburg is dedicated to the study of external seeding techniques. In this paper, the layout of the sFLASH seeding experiment is presented and an overview of recent developments is given.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-FEL2019-TUP076
About •	paper received ※ 30 September 2019 paper accepted ※ 17 October 2019 issue date ※ 05 November 2019
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TUP077	Study of a Seeded Oscillator-Amplifier FEL	laser, electron, simulation, free-electron-laser	234
	G. Paraskaki, S. Ackermann, B. Faatz, V. Grattoni, C. Lechner, M. Mehrjoo DESY, Hamburg, Germany G. Geloni, S. Serkez, T. Tanikawa EuXFEL, Schenefeld, Germany W. Hillert University of Hamburg, Institut für Experimentalphysik, Hamburg, Germany
	In recent years, there is interest of the Free-Electron Laser (FEL) community in external-seeding techniques such as the Echo-Enabled Harmonic Generation (EEHG) and the High-Gain Harmonic Generation (HGHG). With these techniques, pulses of an improved temporal coherence are generated, but at the same time, they are limited by the repetition rates that seed lasers can currently offer with the required pulse energies. A big challenge is to combine the advantages of seeding schemes with high repetition rates. For this purpose, we study a combination of an oscillator-amplifier. The modulator in the oscillator is used at a long wavelength to modulate the electron beam and an amplifier is operated to extract the FEL radiation of the desired harmonic. This way we can use a seed laser of 10 Hz in a burst mode and a resonator to feedback the radiation at repetition rates of superconducting accelerators instead of using an external seed at these high-repetition rates. In this contribution, we present simulation results of a seeded oscillator-amplifier FEL in an HGHG scheme.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-FEL2019-TUP077
About •	paper received ※ 19 August 2019 paper accepted ※ 29 August 2019 issue date ※ 05 November 2019
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TUP078	Impact of Electron Beam Energy Chirp on Seeded FELs	electron, laser, simulation, timing	238
	G. Paraskaki, S. Ackermann, B. Faatz, V. Grattoni, C. Lechner, J. Zemella DESY, Hamburg, Germany W. Hillert University of Hamburg, Institut für Experimentalphysik, Hamburg, Germany
	Seeded FELs enable the generation of fully coherent, transform-limited and high brightness FEL pulses, as the start-up process is driven by an external coherent light pulse. During the design process of such FELs, it is important to choose carefully the electron beam parameters to guarantee high performance. One of those parameters is the electron beam energy chirp. In this contribution, we show simulation results and we discuss how the electron beam energy chirp affects the final spectrum.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-FEL2019-TUP078
About •	paper received ※ 16 August 2019 paper accepted ※ 28 August 2019 issue date ※ 05 November 2019
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TUP079	Status of the Hard X-Ray Self-Seeding Setup at the European XFEL	undulator, electron, radiation, simulation	242
	G. Geloni, S. Karabekyan, D. La Civita, L. Samoylova, S. Serkez, R. Shayduk, H. Sinn, V. Sleziona, M. Vannoni, M. Yakopov EuXFEL, Schenefeld, Germany J.W.J. Anton, S.P. Kearney, D. Shu ANL, Lemont, Illinois, USA V.D. Blank, S. Terentiev TISNCM, Troitsk, Russia W. Decking, V. Kocharyan, S. Liu, E. Negodin, E. Saldin, T. Wohlenberg DESY, Hamburg, Germany X. Dong European X-Ray Free-Electron Laser Facility GmbH, Schelefeld, Germany
	A Hard X-Ray Self-Seeding (HXRSS) setup will be soon commissioned at the European XFEL. It relies on a two-chicanes scheme to deal, in particular, with the high pulse repetition rate of the facility. In this contribution we review the physics choices made at the design stage and the expected performance of the setup. We will also focus on the description of the hardware installations made at the SASE2 line of the European XFEL.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-FEL2019-TUP079
About •	paper received ※ 27 August 2019 paper accepted ※ 28 August 2019 issue date ※ 05 November 2019
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TUP083	Energy Spread Impact on HGHG and EEHG FEL Pulse Energy	laser, electron, bunching, photon	250
	S. Spampinati, E. Allaria, L. Giannessi, P. Rebernik Ribič Elettra-Sincrotrone Trieste S.C.p.A., Basovizza, Italy L. Giannessi ENEA C.R. Frascati, Frascati (Roma), Italy P. Rebernik Ribič University of Nova Gorica, Nova Gorica, Slovenia
	VUV and X-ray free electron lasers (FELs) require a very bright electron beam. Seeded FEL harmonic generation is particularly sensible to energy spread and slice energy spread can limit the highest harmonic conversion factor at which coherent radiation can be produced. Different cas-cade schemes can have different sensibility to the slice energy spread. At FERMI we have evaluated the impact of the slice energy spread on the performance of high gain harmonic generation (HGHG) and of echo enable harmonic generation (EEHG) by measuring the FEL pulse energy as function of the electron beam slice energy spread. The measurements were done at different harmon-ics. The slice energy spread was varied trough the laser heater located in the linac that drives FERMI.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-FEL2019-TUP083
About •	paper received ※ 20 August 2019 paper accepted ※ 17 September 2019 issue date ※ 05 November 2019
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TUP087	Start-to-end Simulations of the Reflection Hard X-Ray Self-Seeding at the SHINE Project	undulator, photon, simulation, electron	254
	T. Liu, X. Dong, C. Feng SARI-CAS, Pudong, Shanghai, People’s Republic of China
	The Shanghai high repetition rate XFEL and extreme light Facility (SHINE) project is designed to produce fully coherent X-ray photons covering the photon energy from 3 keV to 25 keV. We have reported our FEL proposal and schemes in the hard X-ray regime which is self-seeding based on the crystal monochromator previously. Comparing to the transmission self-seeding scheme, the reflection one has several advantages and might be the base proposal. Start-to-end (S2E) simulations from the beam generation by Astra, the linac accelerating by Elegant to the FEL simulation by Genesis are performed. In this manuscript, the FEL simulations based on the S2E beam will be presented mainly. The results demonstrate the feasibility of the reflection hard X-ray self-seeding at the SHINE project.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-FEL2019-TUP087
About •	paper received ※ 20 August 2019 paper accepted ※ 29 August 2019 issue date ※ 05 November 2019
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TUP088	Numerical Simulations for Generating Fully Coherent Soft X-Ray Free Electron Lasers With Ultra-Short Wavelength	electron, laser, radiation, free-electron-laser	258
	K.S. Zhou, H.X. Deng, B. Liu, D. Wang SARI-CAS, Pudong, Shanghai, People’s Republic of China
	For the fully coherent, ultra-short and high power soft X-rays are becoming key instruments in many different research fields, such as biology, chemistry or physics. However, it’s hard to generate this kind of advanced light source by the conventional lasers, especially for the soft X-rays with ultra-short wavelength because of no suitable reflectors. The external seeded free electron laser (FEL) is considered as one feasible method. Here, we give an example to generate highly temporal coherent soft X-rays with the wavelength 1 nm by the two-stage cascaded schemes. EEHG scheme is used as the first-stage while the HGHG scheme is used as the second-stage.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-FEL2019-TUP088
About •	paper received ※ 20 August 2019 paper accepted ※ 22 October 2019 issue date ※ 05 November 2019
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TUP090	Considerations on Implementing EEHG with a Strong Linear Chirp	electron, laser, simulation, bunching	262
	M.A. Pop, F. Curbis, W. Qin, S. Werin MAX IV Laboratory, Lund University, Lund, Sweden F. Curbis, S. Werin SLF, Lund, Sweden W. Qin Lund University, Lund, Sweden
	Funding: The work is supported by Knut and Alice Wallenberg foundation. The Soft X-ray Laser (SXL) currently being studied at MAX IV Laboratory is envisioned to produce coherent radiation in the 1-5 nm wavelength range. In this contribution, we present the results of simulations aimed at adding to the SXL an Echo Enabled Harmonic Generation scheme, which has been shown to increase the coherence of FELs in the Soft X-ray regime. Our work puts special emphasis on accommodating the positive energy chirp of the electron bunch coming out of the MAX IV Linac and on generating sufficient bunching at the high harmonics necessary for covering the full wavelength range.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-FEL2019-TUP090
About •	paper received ※ 20 August 2019 paper accepted ※ 28 August 2019 issue date ※ 05 November 2019
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TUP091	Start-to-End Simulation of the NSRRC Seeded VUV FEL	laser, electron, undulator, simulation	266
	S.Y. Teng NTHU, Hsinchu, Taiwan C.H. Chen, W.K. Lau, A.P. Lee NSRRC, Hsinchu, Taiwan
	A free electron laser (FEL) driven by a high brightness electron linac system has been proposed to generate ultrashort intense coherent radiation in the vacuum ultraviolet region. It is a third harmonic high-gain high harmonic generation (HGHG) FEL for generation of VUV radiation with wavelength at 66.7 nm from a 20-mm period length helical undulator. A 200-nm seed laser is used for beam energy modulation in a 10-periods helical undulator of 24-mm period length. A small chicane is placed between the two undulators to optimize power growth in the radiator. In this study, we perform start-to-end simulation to foresee the operational performance of the test facility and preliminary results are presented.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-FEL2019-TUP091
About •	paper received ※ 20 August 2019 paper accepted ※ 28 August 2019 issue date ※ 05 November 2019
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TUP092	XFEL Third Harmonic Statistics Measurement at LCLS	photon, undulator, experiment, radiation	269
	A. Halavanau, C. Emma, E. Hemsing, A.A. Lutman, G. Marcus, C. Pellegrini SLAC, Menlo Park, California, USA
	We investigate the statistical properties of the 6 keV third harmonic XFEL radiation at 2 keV fundamental photon energy at LCLS. We performed third harmonic self-seeding in the hard X-ray self-seeding chicane and characterized the attained non-linear third harmonic spectrum. We compare theoretical predictions with experimental results.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-FEL2019-TUP092
About •	paper received ※ 20 August 2019 paper accepted ※ 29 August 2019 issue date ※ 05 November 2019
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TUD02	Application of Infrared FEL Oscillators for Producing Isolated Attosecond X-Ray Pulses via High-Harmonic Generation in Rare Gases	cavity, laser, experiment, photon	272
	R. Hajima, K. Kawase, R. Nagai QST, Tokai, Japan Y. Hayakawa, T. Sakai, Y. Sumitomo LEBRA, Funabashi, Japan T. Miyajima, M. Shimada KEK, Ibaraki, Japan H. Ohgaki, H. Zen Kyoto University, Kyoto, Japan
	Funding: Quantum Leap Flagship Program (MEXT Q-LEAP) High harmonic generation (HHG) in rare gases is now becoming a common technology to produce attosecond pulses in VUV wavelengths. So far HHG sources have been realized by femtosecond solid-state lasers, not FELs. We propose a FEL-driven HHG source to explore attosecond pulses at photon energies above 1 keV with a MHz-repetition, which is difficult with solid-state lasers [1]. A research program has been launched to establish technologies for the FEL-HHG, which covers generation and characterization of few-cycle IR pulses in a FEL oscillator, stacking of FEL pulses in an external cavity, and a seed laser for stabilization of carrier-envelope phase in a FEL oscillator. In this talk, we present the scheme of FEL-HHG and the status of the research program. [1] R. Hajima and R. Nagai, Phys. Rev. Lett. 119, 204802 (2017)
	Slides TUD02 [8.995 MB]
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-FEL2019-TUD02
About •	paper received ※ 23 August 2019 paper accepted ※ 29 August 2019 issue date ※ 05 November 2019
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TUD03	Fine and Hyperfine Structure of FEL Emission Spectra	electron, radiation, laser, experiment	276
	V.V. Kubarev, Ya.V. Getmanov, O.A. Shevchenko BINP SB RAS, Novosibirsk, Russia S. Bae, Y.U. Jeong KAERI, Daejon, Republic of Korea
	This paper presents the results of experimental investigations of the fine and hyperfine spectral structures of the Novosibirsk free-electron laser (NovoFEL) and the compact free-electron laser of the Korea Atomic Energy Research Institute (KAERI FEL) by means of the optimal instruments, resonance Fabry-Perot interferometers. The very high coherence of the NovoFEL spectrum was measured in regimes with one pulse circulating inside its optical resonator (the coherence length is 7 km, and the relative width of the hyperfine structure lines is 2E-8) and with total absence of coherence between two circulating pulses, i.e. the fine structure. Sixty pulses circulate simultaneously inside the KAERI FEL optical resonator, and the measured coherence length on average covers ten pulses (the coherence length is 1 m; the relative width of the fine structure lines is 10^-4).
	Slides TUD03 [3.177 MB]
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-FEL2019-TUD03
About •	paper received ※ 16 August 2019 paper accepted ※ 29 August 2019 issue date ※ 05 November 2019
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TUD04	Cavity-Based Free-Electron Laser Research and Development: A Joint Argonne National Laboratory and SLAC National Laboratory Collaboration	electron, cavity, undulator, laser	282
	G. Marcus, F.-J. Decker, G.L. Gassner, A. Halavanau, J.B. Hastings, Z. Huang, Y. Liu, J.P. MacArthur, R.A. Margraf, T.O. Raubenheimer, A. Sakdinawat, T.-F. Tan, D. Zhu SLAC, Menlo Park, California, USA J.W.J. Anton, L. Assoufid, K. Goetze, W.G. Jansma, S.P. Kearney, K. Kim, R.R. Lindberg, A. Miceli, X. Shi, D. Shu, Yu. Shvyd’ko, J.P. Sullivan, M. White ANL, Lemont, Illinois, USA B. Lantz Stanford University, Stanford, California, USA
	One solution for producing longitudinally coherent FEL pulses is to store and recirculate the output of an amplifier in an X-ray cavity so that the X-ray pulse can interact with following fresh electron bunches over many passes. The X-ray FEL oscillator (XFELO) and the X-ray regenerative amplifier FEL (XRAFEL) concepts use this technique and rely on the same fundamental ingredients to realize their full capability. Both schemes require a high repetition rate electron beam, an undulator to provide FEL gain, and an X-ray cavity to recirculate and monochromatize the radiation. The shared infrastructure, complementary performance characteristics, and potentially transformative FEL properties of the XFELO and XRAFEL have brought together a joint Argonne National Laboratory (ANL) and SLAC National Laboratory (SLAC) collaboration aimed at enabling these schemes at LCLS-II. We present plans to install a rectangular X-ray cavity in the LCLS-II undulator hall and perform experiments employing 2-bunch copper RF linac accelerated electron beams. This includes performing cavity ring-down measurements and 2-pass gain measurements for both the low-gain XFELO and the high-gain RAFEL schemes.
	Slides TUD04 [12.425 MB]
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-FEL2019-TUD04
About •	paper received ※ 25 August 2019 paper accepted ※ 29 August 2019 issue date ※ 05 November 2019
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TUT01	Superradiance and Stimulated-Superradiant Emission of Bunched Electron Beams	radiation, electron, wiggler, undulator	288
	A. Gover, R. Ianconescu University of Tel-Aviv, Faculty of Engineering, Tel-Aviv, Israel C. Emma, P. Musumeci, C. Pellegrini, N.S. Sudar UCLA, Los Angeles, USA A. Friedman Ariel University, Ariel, Israel R. Ianconescu Shenkar College of Engineering and Design, Ramat Gan, Israel
	Funding: We acknowledge support of the Israel Science Foundation and the German Israeli Projects Foundation (DIP). We outline the fundamental processes of coherent radiation emission from a bunched charged particles beam [1]. In contrast to spontaneous emission of radiation from a random electron beam that is proportional to the number of particles N, a pre-bunched electron beam emits spontaneously coherent radiation proportional to N² through the process of (spontaneous) superradiance (SP-SR) (in the sense of Dicke’s [2]). The SP-SR emission of a bunched electron beam can be even further enhanced by a process of stimulated-superradiance (ST-SR) in the presence of a seed injected radiation field. These coherent radiation emission processes are presented in term of a radiation mode expansion model, applied to general free electron radiation schemes: Optical-Klystron, HGHG, EEHG, and coherent THz sources based on synchrotron radiation, undulator radiation or Smith-Purcell radiation. The general model of coherent spontaneous emission is also extended to the nonlinear regime - Tapering Enhanced Stimulated Superradiance (TESSA) [3], and related to the tapered wiggler section of seed-injected FELs. In X-Ray FELs these processes are convoluted with other effects, but they are guidelines for strategies of wiggler tapering efficiency enhancement. [1] A. Gover et al., Rev. Mod. Phys. https://arxiv.org/abs/1810.07566v3 (2019) [2] R. H. Dicke, Physical Review 93, 99 (1954) [3] N. Sudar et al., P.R.L. 117, 174801 (2016)
	Slides TUT01 [11.391 MB]
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-FEL2019-TUT01
About •	paper received ※ 20 August 2019 paper accepted ※ 29 August 2019 issue date ※ 05 November 2019
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WEA01	Overview of CW RF Guns for Short Wavelength FELs	gun, cathode, SRF, electron	290
	H.J. Qian DESY Zeuthen, Zeuthen, Germany E. Vogel DESY, Hamburg, Germany
	Hard X-ray FELs (XFELs) operating with pulsed RF provide unprecedented peak brilliance for scientific research. Operating the accelerators with CW RF improves the flexibility w.r.t. the available time structure for experiments and opens the next frontier of average brilliance. One of the challenges of CW XFELs is the electron source, which requires both CW operation and highest possible beam quality allowing lasing at shortest wavelengths. The CW mode technically constraints the gun acceleration gradient, which is one of the keys to electron source brightness, so R&D is devoted to CW gun improvements since decades. In this contribution, the worldwide development status of CW RF guns, both normal conducting and superconducting, is reviewed.
	Slides WEA01 [16.329 MB]
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-FEL2019-WEA01
About •	paper received ※ 25 August 2019 paper accepted ※ 07 November 2019 issue date ※ 05 November 2019
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WEA04	Growing and Characterization of Cs2Te Photocatodes with Different Thicknesses at INFN LASA	cathode, electron, gun, diagnostics	297
	L. Monaco, P. Michelato, D. Sertore INFN/LASA, Segrate (MI), Italy G. Guerini Rocco, C. Pagani Università degli Studi di Milano & INFN, Segrate, Italy
	The INFN LASA group has a long standing experience in the production of cesium telluride photocathodes for high brightness photoinjectors. The well-established recipe relies on the deposition of a typical amount of 10 nm of Te, followed by the Cs deposition until reaching the maximum QE. Nevertheless, for improving the understanding of photocathode properties, we are investigating the effect of Te thickness on the growing process, evaluating photocathode optical properties and quantum efficiency during the growing process and on the final film. These photocathodes will be then operated and analyzed in the real environment of the RF Gun at the PITZ facility in DESY Zeuthen, to estimate their impact on the electron beam properties.
	Slides WEA04 [15.703 MB]
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-FEL2019-WEA04
About •	paper received ※ 20 August 2019 paper accepted ※ 27 August 2019 issue date ※ 05 November 2019
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WEB01	Identification and Mitigation of Smoke-Ring Effects in Scintillator-Based Electron Beam Images at the European XFEL	electron, diagnostics, experiment, ECR	301
	G. Kube, S. Liu, A.I. Novokshonov, M. Scholz DESY, Hamburg, Germany
	Standard transverse beam profile measurements at the European XFEL are based on scintillating screen monitors using LYSO:Ce. While it is possible to resolve beam sizes down to a few micrometers with this scintillator, the experience during the XFEL commissioning showed that the measured emittance values were significantly larger than the expected ones. In addition, beam profiles measured at bunch charges of a few hundred pC showed a ’smoke ring’ structure. While coherent OTR emission and beam dynamical influence can be excluded, it is assumed that the profile distortions are caused by effects from the scintillator material. Following the experience in high energy physics, a simple model was developed which takes into account quenching effects of excitonic carriers inside a scintillator in a heuristic way. Based on this model, the observed beam profiles can be understood qualitatively. Together with the model description, first comparisons with experimental results will be shown. Possible new scintillator materials suitable for beam profile diagnostics and first test results from beam measurements will be presented.

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MOA02

First Lasing of a Free Electron Laser in the Soft X-Ray Spectral Range with Echo Enabled Harmonic Generation

laser, electron, experiment, free-electron-laser

7

E. Allaria, A. Abrami, L. Badano, M. Bossi, N. Bruchon, F. Capotondi, D. Castronovo, M. Cautero, P. Cinquegrana, M. Coreno, I. Cudin, M.B. Danailov, G. De Ninno, A.A. Demidovich, S. Di Mitri, B. Diviacco, W.M. Fawley, M. Ferianis, L. Foglia, G. Gaio, F. Giacuzzo, L. Giannessi, S. Grulja, F. Iazzourene, G. Kurdi, M. Lonza, N. Mahne, M. Malvestuto, M. Manfredda, C. Masciovecchio, N.S. Mirian, I. Nikolov, G. Penco, E. Principi, L. Raimondi, P. Rebernik Ribič, R. Sauro, C. Scafuri, P. Sigalotti, S. Spampinati, C. Spezzani, L. Sturari, M. Svandrlik, M. Trovò, M. Veronese, D. Vivoda, M. Zaccaria, D. Zangrando, M. Zangrando
Elettra-Sincrotrone Trieste S.C.p.A., Basovizza, Italy
H.-H. Braun, E. Ferrari, E. Prat, S. Reiche
PSI, Villigen PSI, Switzerland
N. Bruchon
University of Trieste, Trieste, Italy
M. Coreno
CNR-ISM, Trieste, Italy
M.-E. Couprie, A. Ghaith
SOLEIL, Gif-sur-Yvette, France
G. De Ninno
University of Nova Gorica, Nova Gorica, Slovenia
C. Feng
SARI-CAS, Pudong, Shanghai, People’s Republic of China
F. Frassetto, L.P. Poletto
LUXOR, Padova, Italy
D. Garzella
CEA, Gif-sur-Yvette, France
V. Grattoni
DESY, Hamburg, Germany
E. Hemsing
SLAC, Menlo Park, California, USA
P. Miotti
CNR-IFN, Padova, Italy
G. Penn
LBNL, Berkeley, California, USA
M.A. Pop
MAX IV Laboratory, Lund University, Lund, Sweden
E. Roussel
PhLAM/CERCLA, Villeneuve d’Ascq Cedex, France
T. Tanikawa
EuXFEL, Schenefeld, Germany
D. Xiang
Shanghai Jiao Tong University, Shanghai, People’s Republic of China

We report on the successful operation of a Free Electron Laser (FEL) in the Echo Enabled Harmonic Generation (EEHG) scheme at the FERMI facility at Sincrotrone Trieste. The experiment required a modification of the FEL-2 undulator line which, in normal operation, uses two stages of high-gain harmonic generation separated by a delay line. In addition to a new seed laser, the dispersion in the delay-line was increased, the second stage modulator changed and a new manipulator installed in the delay-line chicane hosting additional diagnostic components. With this modified setup we have demonstrated the first evidence of strong exponential gain in a free electron laser operated in EEHG mode at wavelengths as short as 5 nm.

Slides MOA02 [5.133 MB]

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reference for this paper ※ https://doi.org/10.18429/JACoW-FEL2019-MOA02

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paper received ※ 21 August 2019 paper accepted ※ 28 August 2019 issue date ※ 05 November 2019

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MOA03

First Lasing at the CAEP THz FEL Facility

electron, laser, free-electron-laser, high-voltage

11

P. Li, T.H. He, M. Li, J. Liu, X. Luo, Q. Pan, L.J. Shan, X. Shen, H. Wang, J. Wang, D. Wu, D.X. Xiao, Y. Xu, L.G. Yan, P. Zhang, K. Zhou
CAEP/IAE, Mianyang, Sichuan, People’s Republic of China
Y. Liu
CAEP/IFP, Mainyang, Sichuan, People’s Republic of China

China Academy of Engineering Physics terahertz free electron laser (CAEP THz FEL, CTFEL) is the first THz FEL user facility in China, which was an oscillator type FEL. This THz FEL facility consists of a GaAs photocathode high-voltage DC gun, a superconducting RF linac, a planar undulator and a quasi-concentric optical resonator. The terahertz laser’s frequency is continuous adjustable from 0.7 THz to 4.2 THz. The average power is more than 10 W and the micro-pulse power is more than 0.3 MW. In this paper, the specific parameters and operation status of CTFEL are presented. Finally, some user experiments are introduced briefly.

Slides MOA03 [3.771 MB]

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reference for this paper ※ https://doi.org/10.18429/JACoW-FEL2019-MOA03

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paper received ※ 20 August 2019 paper accepted ※ 18 September 2019 issue date ※ 05 November 2019

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MOA07

Commissioning and First Lasing of the FELiChEM: A New IR and THz FEL Oscillator in China

electron, cavity, undulator, linac

15

H.T. Li, Q.K. Jia
USTC/NSRL, Hefei, Anhui, People’s Republic of China

A new infrared FEL named FELiChEM aiming at the energy chemistry has been constructed and commissioned at NSRL in Hefei. It consists of two FEL oscillators driven by one normal-conducting S-Band linac with maximum beam energy of 60 MeV. The two oscillators generate the midinfrared and far-infrared lasers covering the spectral range of 2.5-50 µm and 40-200 µm, respectively. First lasing was achieved at a wavelength of 15 µm with an electron energy of 35 MeV. Till now, we have observed the FEL signal from 3.5 µm to 30 µm and achieved the maximum micropulse energy up to 27 µJ at 15 µm.

Slides MOA07 [2.434 MB]

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reference for this paper ※ https://doi.org/10.18429/JACoW-FEL2019-MOA07

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paper received ※ 20 August 2019 paper accepted ※ 28 August 2019 issue date ※ 05 November 2019

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MOC01

Regenerative Amplifier FEL - from IR to X-Rays

cavity, undulator, electron, feedback

20

D.C. Nguyen, P.M. Anisimov, C.E. Buechler, Q.R. Marksteiner, R.L. Sheffield
LANL, Los Alamos, New Mexico, USA

The Regenerative Amplifier FEL (RAFEL) feeds back a small fraction of the radiation exiting a high-gain undulator as the seed for the next pass, and achieves narrow linewidth and saturation in a few passes. For the IR RAFEL, we used an optical cavity with annular mirrors to reinject ~10% of the IR radiation back into a two-meter undulator [1]. Since then, a number of researchers have proposed RAFEL and XFELO to achieve full temporal coherence in VUV and X-ray FELs [2-5]. For the XFELO, symmetric Bragg backscattering off high-quality diamond crystals can provide very high reflectivity for the XFELO cavity [6]. The required reflectivity for a RAFEL feedback cavity is much lower than the XFELO. We show that 6% feedback is sufficient for the X-ray RAFEL at 9.8 keV to saturate and achieve 0.5-eV bandwidth. We discuss options to out-couple more than ~50% of the RAFEL intra-cavity power and discuss challenges associated with X-ray absorption in the out-coupler.
[1] D. Nguyen et al. NIMA 429 125 (1999)
[2] B. Faatz et al. NIMA A429 424 (1999)
[3] Z. Huang et al. PRL 96 144801 (2006)
[4] B.W.J. McNeil et al. NJP 9 239 (2007)
[5] G. Marcus et al. FEL17 MOP061 (2017)
[6] K. Kim et al. PRL 100 244802 (2008)

Slides MOC01 [1.260 MB]

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reference for this paper ※ https://doi.org/10.18429/JACoW-FEL2019-MOC01

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paper received ※ 21 August 2019 paper accepted ※ 28 August 2019 issue date ※ 05 November 2019

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TUA01

Parallel Operation of SASE1 and SASE3 at the European XFEL

background, operation, electron, undulator

25

S. Liu, F. Brinker, W. Decking, L. Fröhlich, R. Kammering, D. Nölle, F. Obier, E. Schneidmiller, M. Scholz, T. Wilksen, M.V. Yurkov
DESY, Hamburg, Germany
R. Boll, N. Gerasimova, T. Mazza, M. Meyer, A. Scherz, H. Sinn
EuXFEL, Schenefeld, Germany

At the European XFEL a hard X-Ray SASE FEL (SA-SE1) and a soft X-Ray SASE FEL (SASE3) share in series the same electron beamline. This configuration couples the operation conditions for both undulators and their subsequent user experiments in terms of SASE in-tensity and background. We report on our experience in parallel operation and discuss the solutions that enable the operation of both undulators as independently as possible.

Slides TUA01 [13.809 MB]

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paper received ※ 26 August 2019 paper accepted ※ 17 October 2019 issue date ※ 05 November 2019

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TUA04

Harmonic Lasing Experiment at the European XFEL

undulator, electron, laser, free-electron-laser

29

E. Schneidmiller, F. Brinker, W. Decking, M.W. Guetg, S. Liu, D. Nölle, M. Scholz, M.V. Yurkov, I. Zagorodnov
DESY, Hamburg, Germany
G. Geloni, N. Gerasimova, J. Grünert, S. Karabekyan, N.G. Kujala, J. Laksman, Y. Li, J. Liu, Th. Maltezopoulos, I. Petrov, L. Samoylova, S. Serkez, H. Sinn, F. Wolff-Fabris
EuXFEL, Schenefeld, Germany

Harmonic lasing is an opportunity to extend the photon energy range of existing and planned X-ray FEL user facilities. Contrary to nonlinear harmonic generation, harmonic lasing can provide a much more intense, stable, and narrow-band FEL beam. Another interesting application is Harmonic Lasing Self-Seeding (HLSS) that allows to improve the longitudinal coherence and spectral power of a Self-Amplified Spontaneous Emission (SASE) FEL. This concept was successfully tested at FLASH in the range of 4.5 - 15 nm and at PAL XFEL at 1 nm. In this contribution we present recent results from the European XFEL where we successfully demonstrated operation of HLSS FEL at 5.9 Angstrom and 2.8 Angstrom, in the latter case obtaining both 3rd and 5th harmonic lasing.

Slides TUA04 [1.174 MB]

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reference for this paper ※ https://doi.org/10.18429/JACoW-FEL2019-TUA04

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paper received ※ 20 August 2019 paper accepted ※ 29 August 2019 issue date ※ 05 November 2019

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TUB01

Echo-Enabled Harmonic Generation Lasing of the FERMI FEL in the Soft X-Ray Spectral Region

laser, electron, free-electron-laser, photon

33

P. Rebernik Ribič
Elettra-Sincrotrone Trieste S.C.p.A., Basovizza, Italy
P. Rebernik Ribič
University of Nova Gorica, Nova Gorica, Slovenia

The layout of the FERMI FEL-2 undulator line, normally operated in the two-stage high-gain harmonic generation (HGHG) configuration, was temporarily modified to allow running the FEL in the echo-enabled harmonic generation (EEHG) mode. The EEHG setup produced stable, intense and nearly fully coherent pulses at wavelengths as short as 5.9 nm (211 eV). Comparing the performance to the two-stage HGHG showed that EEHG gives significantly better spectra in terms of the central wavelength stability and bandwidth, especially at high harmonics, where electron-beam imperfections start to play a significant role. Observation of stable, narrow-band, coherent emission down to 2.6 nm (474 eV) indicates the possibility to extend the lasing region to even shorter wavelengths.

Slides TUB01 [10.360 MB]

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reference for this paper ※ https://doi.org/10.18429/JACoW-FEL2019-TUB01

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paper received ※ 21 August 2019 paper accepted ※ 29 August 2019 issue date ※ 05 November 2019

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TUP001

Extension of the PITZ Facility for a Proof-of-Principle Experiment on THz SASE FEL

radiation, undulator, electron, experiment

38

P. Boonpornprasert, G.Z. Georgiev, G. Koss, M. Krasilnikov, X. Li, F. Mueller, A. Oppelt, S. Philipp, H. Shaker, F. Stephan, T. Weilbach
DESY Zeuthen, Zeuthen, Germany
Z.G. Amirkhanyan
CANDLE SRI, Yerevan, Armenia

The Photo Injector Test Facility at DESY in Zeuthen (PITZ) has been proposed as a suitable facility for research and development of an accelerator-based THz source prototype for pump-probe experiments at the European XFEL. A proof-of-principle experiment to generate THz SASE FEL radiation by using an LCLS-I undulator driven by an electron bunch from the PITZ accelerator has been planned and studied. The undulator is foreseen to be installed downstream from the current PITZ accelerator, and an extension of the accelerator tunnel is necessary. Radiation shielding for the extended tunnel was designed, and construction works are finished. Design of the extended beamline is ongoing, not only for this experiment but also for other possible experiments. Components for the extended beamline, including magnets for beam transport, a chicane bunch compressor, electron beam diagnostics devices, and THz radiation diagnostics devices have been studied. An overview of these works will be presented in this paper.

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reference for this paper ※ https://doi.org/10.18429/JACoW-FEL2019-TUP001

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paper received ※ 20 August 2019 paper accepted ※ 28 August 2019 issue date ※ 05 November 2019

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TUP002

Progress in Preparing a Proof-of-Principle Experiment for THz SASE FEL at PITZ

laser, undulator, experiment, flattop

41

X. Li, P. Boonpornprasert, Y. Chen, G.Z. Georgiev, J.D. Good, M. Groß, P.W. Huang, I.I. Isaev, C. Koschitzki, M. Krasilnikov, S. Lal, O. Lishilin, G. Loisch, D. Melkumyan, R. Niemczyk, A. Oppelt, H.J. Qian, H. Shaker, G. Shu, F. Stephan, G. Vashchenko
DESY Zeuthen, Zeuthen, Germany

A proof-of-princle experiment for a THz SASE FEL is undergoing preparation at the Photo Injector Test facility at DESY in Zeuthen (PITZ), as a prototype THz source for pump-probe experiments at the European XFEL, which could potentially provide up to mJ/pulse THz radiation while maintaining the identical pulse train structure as the XFEL pulses. In the proof-of-principle experiment, LCLS-I undulators will be installed to generate SASE radiation in the THz range of 3-5 THz from electron bunches of 16-22 MeV/c. One key design is to obtain the peak current of nearly 200 A from the heavily charged bunches of a few nC. In this paper, we report our simulation results on the optimization of the space charge dominated beam in the photo injector and the following transport line with two cathode laser setups. Experimental results based on a short Gaussian laser will also be discussed.

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reference for this paper ※ https://doi.org/10.18429/JACoW-FEL2019-TUP002

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paper received ※ 20 August 2019 paper accepted ※ 27 August 2019 issue date ※ 05 November 2019

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TUP003

Design of a Magnetic Bunch Compressor for the THz SASE FEL Proof-of-Principle Experiment at PITZ

radiation, dipole, experiment, undulator

45

H. Shaker, P. Boonpornprasert, G.Z. Georgiev, G. Koss, M. Krasilnikov, X. Li, A. Lueangaramwong, F. Mueller, A. Oppelt, S. Philipp, F. Stephan, G. Vashchenko, T. Weilbach
DESY Zeuthen, Zeuthen, Germany

For pump-probe experiments at the European XFEL, a THz source is required to produce intense THz pulses at the same repetition rate as the X-ray pulses from XFEL. Therefore, an accelerator-based THz source with identical electron source as European XFEL was suggested and proof-of-principle experiments utilizing an LCLS I undulator will be performed at the Photo Injector Test Facility at DESY in Zeuthen (PITZ). The main idea is to use a 4nC beam for maximum SASE radiation but to allow different radiation regimes a magnetic bunch compressor can be used. This helps e.g. to reduce the saturation length inside the undulator and also to study super-radiant THz radiation. In this paper a design of a chicane type magnetic bunch compressor using HERA corrector magnets is presented.

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reference for this paper ※ https://doi.org/10.18429/JACoW-FEL2019-TUP003

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paper received ※ 20 August 2019 paper accepted ※ 27 August 2019 issue date ※ 05 November 2019

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TUP004

A Superradiant THz Undulator Source for XFELs

undulator, electron, radiation, experiment

48

T. Tanikawa, G. Geloni, S. Karabekyan, S. Serkez
EuXFEL, Schenefeld, Germany
V.B. Asgekar
University of Pune, Pune, India
S. Casalbuoni
KIT, Eggenstein-Leopoldshafen, Germany
M. Gensch
Technische Universität Berlin, Berlin, Germany
M. Gensch
DLR, Berlin, Germany
S. Kovalev
HZDR, Dresden, Germany

The European XFEL has successfully achieved first lasing in 2017 and meanwhile three SASE FEL beamlines are in operation. An increasing number of users has great interest in a specific type of two-color pump-probe experiments in which high-field THz pulses are employed to drive nonlinear processes and dynamics in matter selectively. Here, we propose to use a 10-period superconducting THz undulator to provide intense, narrowband light pulses tunable in wide range between 3 and 100 THz. The exploitation of superconducting technology allows us to meet the challenge of generating such low photon energy radiation despite the very high electron beam energy at the European XFEL. In this presentation, we will present the latest development concerning THz undulator design and present the expected THz pulse properties for the case of the European XFEL.

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paper received ※ 20 August 2019 paper accepted ※ 27 August 2019 issue date ※ 05 November 2019

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TUP006

The FHI FEL Upgrade Design

undulator, cavity, dipole, kicker

52

W. Schöllkopf, M. De Pas, D. Dowell, S. Gewinner, H. Junkes, G. Meijer, G. von Helden
FHI, Berlin, Germany
W.B. Colson
NPS, Monterey, California, USA
S.C. Gottschalk
STI Magnetics LLC, Woodinville, USA
J. Rathke, T. Schultheiss
AES, Medford, New York, USA
A.M.M. Todd
AMMTodd Consulting, Princeton Junction, New Jersey, USA
L.M. Young
LMY Technology, Lincolnton, Georgia, USA

Since coming on-line in November 2013, the Fritz-Haber-Institut (FHI) der Max-Planck-Gesellschaft (MPG) Free-Electron Laser (FEL) has provided intense, tunable infrared radiation to FHI user groups. It has enabled experiments in diverse fields ranging from bio-molecular spectroscopy to studies of clusters and nanoparticles, nonlinear solid-state spectroscopy, and surface science, resulting in 50 peer-reviewed publications so far. A significant upgrade of the FHI FEL is now being prepared. A second short Rayleigh range undulator FEL beamline is being added that will permit lasing from < 5 microns to > 160 microns. Additionally, a 500 MHz kicker cavity will permit simultaneous two-color operation of the FEL from both FEL beamlines over an optical range of 5 to 50 microns by deflecting alternate 1 GHz pulses into each of the two undulators. We will describe the upgraded FHI FEL physics and engineering design and present the plans for two-color FEL operations in November 2020.

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paper received ※ 20 August 2019 paper accepted ※ 27 August 2019 issue date ※ 05 November 2019

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TUP008

Concept of High-Power CW IR-THz Source for the Radiation Source Elbe Upgrade

undulator, electron, radiation, linac

59

P.E. Evtushenko, T.E. Cowan, U. Lehnert, P. Michel
HZDR, Dresden, Germany

The Radiation Source ELBE at HZDR is a user facility based on a 1 mA, 40 MeV CW SRF LINAC. HZDR is considering upgrade options for the ELBE or its replacement with a new user facility. A part of the user requirements is the capability to generate IR and THz pulse in the frequency range from 0.1 through 30 THz, with pulse energies in the range from 100 uJ through a few mJ, at the repetition rate between 100 kHz and 1 MHz. In this contribution, we outline key aspects of a concept, which would allow achieving such parameters. Such key aspects are: use of a beam with longitudinal density modulation and bunching factor of about 0.5 at the fundamental frequency; achieving the density modulation through the mechanism similar to the one used in optical klystron (OK) and HGHG FEL, generation necessary for the modulation optical beam by an FEL oscillator, using two electron injectors, where one injector provides a beam for the FEL oscillator while second high charge injector provides beam for the high energy per pulse generation for user experiments. All-in-all the concept of the new radiation source is very similar to an OK, but operating with two beams simultaneously.

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reference for this paper ※ https://doi.org/10.18429/JACoW-FEL2019-TUP008

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paper received ※ 29 August 2019 paper accepted ※ 29 August 2019 issue date ※ 05 November 2019

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TUP009

Integration of an XFELO at the European XFEL Facility

electron, radiation, simulation, cavity

62

P. Rauer, I. Bahns, W. Hillert, J. Roßbach
University of Hamburg, Institut für Experimentalphysik, Hamburg, Germany
W. Decking
DESY, Hamburg, Germany
H. Sinn
EuXFEL, Schenefeld, Germany

Funding: Work supported by BMBF (FKZ 05K16GU4)
An X-ray free-electron laser oscillator (XFELO) is a fourth generation X-ray source promising radiation with full three dimensional coherence, nearly constant pulse to pulse stability and more than an order of magnitude higher peak brilliance compared to SASE FELs. Proposed by Kim et al. in 2008 [1] an XFELO follows the concept of circulating the light in an optical cavity - as known from FEL oscillators in longer wavelength regimes - but uses Bragg reflecting crystals instead of classical mirrors. With the new European X-ray Free-Electron Laser (XFEL) facility recently gone into operation, the realization of an XFELO with radiation in the Angstrom regime seems feasible. Though, the high thermal load of the radiation on the cavity crystals, the high sensibility of the Bragg-reflection on reflection angle and crystal temperature as well as the very demanding tolerances of the at least 60 m long optical resonator path pose challenges which need to be considered. In this work these problems shall be summarized and results regarding the possible integration of an XFELO at the European XFEL facility will be presented.
[1] K.-J. Kim, Y. Shvyd’ko and S. Reiche, Phys. Rev. Lett. 100 (2008), 244802.

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paper received ※ 20 August 2019 paper accepted ※ 29 August 2019 issue date ※ 05 November 2019

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TUP015

Design of High-Repetition Terahertz Super-Radiation Based on CAEP THz FEL Superconducting Beamline

radiation, electron, undulator, laser

73

D. Wu, T.H. He, L.B. Li, M. Li, P. Li, X. Luo, Q. Pan, L.J. Shan, X. Shen, H. Wang, J. Wang, D.X. Xiao, L.G. Yan, P. Zhang, K. Zhou
CAEP/IAE, Mianyang, Sichuan, People’s Republic of China

China Academy of Engineering Physics terahertz free electron laser (CAEP THz FEL, CTFEL) is the first THz FEL oscillator in China. CTFEL spectrum covers from 0.7 THz to 4.2 THz. However, there are still many applications requiring lower frequency. The super-radiation of the ultra-short electron beam bunches could generate ultra-fast, carrier-envelope-phase-stable, and high-field terahertz. The coherent diffraction/transition radiation (CDR/CTR) and coherent undulator radiation (CUR) can be also synchronized naturally. In this paper, the dynamic and the design of the super-radiation are introduced. The main parameters of the CDR/CTR and CUR are also discussed. A multi-color pump-probe system based on super-radiation is also proposed.
Work supported by National Natural Science Foundation of China with grant (11575264, 11605190 and 11805192), Innovation Foundation of CAEP with grant (CX2019036, CX2019037)

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paper received ※ 20 August 2019 paper accepted ※ 27 August 2019 issue date ※ 05 November 2019

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TUP017

Terahertz FEL Simulation in PAL XFEL

electron, simulation, undulator, radiation

77

J.H. Ko, H.-S. Kang
PAL, Pohang, Republic of Korea

Terahertz radiation is being used in various fields such as imaging, diagnosis, inspection, etc. For the terahertz research, the Pohang accelerator laboratory (PAL) is planning to make a terahertz free electron laser based on self-amplified spontaneous emission (SASE). Using free electron laser method, we can conduct the THz-pump X-ray probe experiment. For the terahertz free electron laser, we conducted the simulation on accelerators below 40 MeV, using photo-cathode RF gun, S-band accelerator and undulator below 4 meters.

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paper received ※ 20 August 2019 paper accepted ※ 25 August 2019 issue date ※ 05 November 2019

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TUP019

Regime of Multi-Stage Non-Resonant Trapping in Free Electron Lasers

electron, FEM, wiggler, experiment

83

A.V. Savilov, I.V. Bandurkin, Yu.S. Oparina, N.Yu. Peskov
IAP/RAS, Nizhny Novgorod, Russia

Funding: This work is supported by the RFBR (grants #18-02-40009, #18-02-00765) and by the IAP RAS Project 0035-2019-0001.
We describe three works united by the idea of the non-resonant regime [1] providing an effective trapping in a beam with a great energy spread. In this regime, the "bucket" corresponding to the resonant electron-wave interaction passes through the electron layer on the energy-phase plane and traps a fraction of electrons. (I) Operability of this regime was demonstrated in the high-efficient 0.8 MeV Ka-band FEM-amplifier [2]. (II) In short-wavelength FELs the multi-stage trapping in several consecutive sections can be organized [3]. In each section a small e-beam fraction is trapped due to a weak electron-wave interaction. However, repetition of this process from section to section involves in the interaction almost the whole e-beam. We describe efficiency enhancement and improving the frequency wave spectrum in multi-stage SASE FELs. (III) The multi-stage amplification of a single-frequency wave signal can provide cooling of the electron bunch. In this regime, tapering of every section is provided such that the "bucket" goes from maximal initial electron energy down to the minimal one and moves down energies of trapped electrons.
[1] A.Savilov et al., Nucl. Instr. Meth. A, vol. 507, p.158, 2003
[2] A.Kaminsky et al., Int. Conf. IRMMW-THz 2018, art. 4057938
[3] S.Kuzikov, A.Savilov, Phys. Plasmas, vol. 25, p.113114, 2018

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paper received ※ 14 August 2019 paper accepted ※ 27 August 2019 issue date ※ 05 November 2019

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TUP021

Development of Powerful Long-Pulse Terahertz Band FELs Based on Linear Induction Accelerators

electron, simulation, radiation, feedback

91

V.Yu. Zaslavsky, N.S. Ginzburg, A. Malkin, N.Yu. Peskov, A. Sergeev
IAP/RAS, Nizhny Novgorod, Russia
A.V. Arzhannikov, E.S. Sandalov, S.L. Sinitsky, D.I. Skovorodin, A.A. Starostenko
BINP SB RAS, Novosibirsk, Russia

Funding: This work was supported by the Russian Scientific Foundation (RSCF), grant No. 19-12-00212.
The paper is devoted to development of high-power long-pulse THz-band FELs based on new generation of linear induction accelerators which have been elaborated recently at Budker Institute (Novosibirsk). These accelerators generate microsecond electron beams with current at kA-level and energy of 2 to 5 MeV (with a possibility to increase electrons energy up to 20 MeV). Based on this beam, we initiated a new project of multi-MW long-pulse FEL operating in the frequency range of 1 to 10 THz using a wiggler period of 3 to 6 cm. For this FEL oscillator, we suggest a hybrid planar two-mirror resonator consisting of an upstream highly selective advanced Bragg reflector and a downstream weakly reflecting conventional Bragg reflector. Simulations demonstrate that the advanced Bragg reflector based on coupling of propagating and quasi-cutoff waves ensures the mode control at the values of the gap between the corrugated plates forming such resonator up to 20 wavelengths. Simulations of the FEL driven by electron beam generated by the LIU¿2 in the frame of both averaged approach and 3D PIC code demonstrate that the THz radiation power can reach the level of 10 to 20 MW.

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paper received ※ 28 August 2019 paper accepted ※ 28 August 2019 issue date ※ 05 November 2019

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TUP023

Analytical and Numerical Comparison of Different Approaches to the Description of SASE in High Gain FELs

radiation, simulation, undulator, bunching

94

O.A. Shevchenko, N.A. Vinokurov
BINP SB RAS, Novosibirsk, Russia
N.A. Vinokurov
NSU, Novosibirsk, Russia

Correlation function theory which has been developed recently gives rigorous statistical description of the SASE FEL operation. It directly deals with the values averaged over many shots. There are two other approaches which are based either on Vlasov equation or on direct solution of particle motion equations. Both of them use random functions which relate to single shot. To check the validity of these three approaches it might be interesting to compare them with each other. In this paper we present the results of such comparison obtained for the 1-D FEL model. We show that two-particle correlation function approximation is equivalent to the quasilinear approximation of the Vlasov equation approach. These two approximations are in a good agreement with the results of direct solution of particle motion equations at linear and early saturation stages. To obtain this agreement at strong saturation high order harmonics in Vlasov equation have to be taken into account which corresponds to taking into account of three and more particle correlations in the correlation function approach.

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paper received ※ 19 August 2019 paper accepted ※ 25 August 2019 issue date ※ 05 November 2019

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TUP024

Electronic Modulation of the FEL-Oscillator Radiation Power Driven by ERL

radiation, electron, experiment, controls

98

O.A. Shevchenko, E.V. Bykov, Ya.V. Getmanov, S.S. Serednyakov, S.V. Tararyshkin
BINP SB RAS, Novosibirsk, Russia
M.V. Fedin, A.R. Melnikov, S.L. Veber
International Tomography Center, SB RAS, Novosibirsk, Russia
Ya.V. Getmanov, S.S. Serednyakov
NSU, Novosibirsk, Russia

FEL oscillators usually operate in CW mode and produce periodic train of radiation pulses but some user experiments require modulation of radiation power. Conventional way to obtain this modulation is using of mechanical shutters but it cannot provide very short switching time and may lead to decreasing of the radiation beam quality. Another way could be based on the electron beam current modulation but it cannot be used in the ERL. We propose a simple way of fast control of the FEL lasing which is based on periodic phase shift of electron bunches with respect to radiation stored in optical cavity. The phase shift required to suppress lasing is relatively small and it does not change significantly repetition rate. This approach has been realized at NovoFEL facility. It allows to generate radiation macropulses of desirable length down to several microseconds (limited by quality factor of optical cavity and FEL gain) which can be synchronized with external trigger. We present detailed description of electronic power modulation scheme and discuss the results of experiments.

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paper received ※ 20 August 2019 paper accepted ※ 27 August 2019 issue date ※ 05 November 2019

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TUP025

Current Status of Free Electron Laser @ TARLA

electron, cryomodule, cavity, undulator

102

A. Aksoy, Ö. Karslı, C. Kaya, İ.B. Koç
Ankara University, Accelerator Technologies Institute, Golbasi, Turkey
Ö.F. Elçim
Ankara University Institute of Accelerator Technologies, Golbasi, Turkey

Funding: Work supported by Strategy and Budget Department of Turkey with Grand No: 2006K120470
Turkish Accelerator and Radiation Laboratory (TARLA), which is supported by the Presidency Strategy and Budget Directorate of Turkey, aims to be the state of art research instrument for the radiation users from Turkey. Two superconducting accelerating modules of TARLA will drive two different planar undulator magnets with periods of 110 mm (U110) and 35 mm (U35) in order to generate high brightness Continuous Wave (CW) Free Electron Laser (FEL) tunable in between 5-350 µm. In addition, the linac will drive a Bremstrahlung radiation station to generate polarized gamma radiation. Main components of TARLA, such as injector, superconducting accelerating modules and cryoplant are under commissioning currently. In this study, we present current status of the facility in addition to expected FEL performance of the facility.

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paper received ※ 20 August 2019 paper accepted ※ 29 August 2019 issue date ※ 05 November 2019

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TUP026

Unaveraged Simulation of a Regenerative Amplifier Free Electron Laser

undulator, cavity, simulation, electron

106

P. Pongchalee, B.W.J. MᶜNeil
USTRAT/SUPA, Glasgow, United Kingdom
B.W.J. MᶜNeil
Cockcroft Institute, Warrington, Cheshire, United Kingdom

A regenerative amplifier free-electron laser (RAFEL) design and simulation requires the modelling of both the electron-light interaction in the FEL undulator and the optical propagation within the cavity. An unaveraged 3D simulation was used to model the FEL interaction within the undulator using the Puffin code. This allows a broadband, high temporal-resolution of the FEL interaction. The Optical Propagation Code (OPC) was used to model the optical beam propagation within the cavity and diagnostics at the cavity mirrors. This paper presents the optical field conversion method between Puffin and the OPC codes and demonstrates the full model via a VUV-RAFEL simulation.

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paper received ※ 19 August 2019 paper accepted ※ 25 August 2019 issue date ※ 05 November 2019

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TUP027

Modelling Crystal Misaligments for the X-ray FEL Oscillator

cavity, alignment, undulator, simulation

110

R.R. Lindberg
ANL, Lemont, Illinois, USA

Funding: Work supported by U.S. Dept. of Energy Office of Sciences under Contract No. DE-AC02-06CH11357.
The X-ray FEL oscillator has the potential to be a revolutionary new light source providing unprecedented stability in a narrow bandwidth [1]. However, a detailed understanding of cavity tolerance and stability has only begun, and there are presently no suitable simulation tools. To address this issue, we have developed a fast FEL oscillator code that discretizes the field using a Gauss-Hermite mode expansion of the oscillator cavity. Errors in crystal alignment result in a mixing of the modes that is easily modeled with a loss and coupling matrix. We show first results from our code, including the effects of static and time-varying crystal misalignments.
[1] K.-J. Kim, Y. Shvyd’ko, and S. Reiche, PRL 100 244802 (2008)

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TUP028

Power Variations of an X-ray FEL Oscillator in Saturation

electron, simulation, cavity, undulator

114

R.R. Lindberg, K. Kim
ANL, Lemont, Illinois, USA

Funding: Work supported by U.S. Dept. of Energy Office of Sciences under Contract No. DE-AC02-06CH11357.
Basic FEL theory predicts that the fractional power fluctuations of an ideal oscillator in steady state should be given by the ratio of the spontaneous power in the oscillator bandwidth to that stored in the cavity at saturation. For the X-ray FEL oscillator with its narrow bandwidth Bragg crystal mirrors, this ratio is typically a few parts per million, but some simulations have shown evidence of power oscillations on the percent level. We show that this is not related to the well-known sideband instability, but rather is purely numerical and can be eliminated by changing the particle loading. We then briefly discuss to what extent variations in electron beam arrival time may degrade the power stability.

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TUP032

Regenerative Amplification for a Hard X-Ray Free-Electron Laser

cavity, electron, radiation, undulator

118

G. Marcus, Y. Ding, Y. Feng, A. Halavanau, Z. Huang, J. Krzywiński, J.P. MacArthur, R.A. Margraf, T.O. Raubenheimer, D. Zhu
SLAC, Menlo Park, California, USA
V. Fiadonu
Santa Clara University, Santa Clara, California, USA

Funding: This work was supported by the Department of Energy, Laboratory Directed Research and Development program at SLAC National Accelerator Laboratory, under contract DE-AC02-76SF00515.
An X-ray regenerative amplifier FEL (XRAFEL) utilizes an X-ray crystal cavity to provide optical feedback to the entrance of a high-gain undulator. An XRAFEL system leverages gain-guiding in the undulator to reduce the cavity alignment tolerances and targets the production of longitudinally coherent and high peak power and brightness X-ray pulses that could significantly enhance the performance of a standard single-pass SASE amplifier. The successful implementation of an X-ray cavity in the XRAFEL scheme requires the demonstration of X-ray optical components that can either satisfy large output coupling constraints or passively output a large fraction of the amplified coherent radiation. Here, we present new schemes to either actively Q-switch a diamond Bragg crystal through lattice constant manipulation or passively output couple a large fraction of the stored cavity radiation through controlled FEL microbunch rotation. A beamline design study, cavity stability analysis, and optimization will be presented illustrating the performance of potential XRAFEL configurations at LCLS-II/-HE using high-fidelity simulations.

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paper received ※ 24 August 2019 paper accepted ※ 26 August 2019 issue date ※ 05 November 2019

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TUP033

Q-Switching of X-Ray Optical Cavities by Using Boron Doped Buried Layer Under a Surface of a Diamond Crystal

laser, cavity, electron, free-electron-laser

122

J. Krzywiński, Y. Feng, A. Halavanau, Z. Huang, A.M. Kiss, J.P. MacArthur, G. Marcus, T. Sato, D. Zhu
SLAC, Menlo Park, California, USA

Improvement of the longitudinal coherence of X-ray Free Electron Lasers has been the subject of many recent investigations. The XFEL oscillator (XFELO) and Regenerative Amplifier Free-Electron Laser (RAFEL) schemes offer a pathway to fully coherent, high brightness X-ray radiation. The XFELO and RAFEL consist of a high repetition rate electron beam, an undulator and an X-ray crystal cavity to provide optical feedback. The X-ray cavity will be based on diamond crystals in order to manage a high thermal load. We are investigating a ’Q switching’ mechanism that involves the use of a ’Bragg switch’ to dump the X-ray pulse energy built-up inside an X-ray cavity. In particular, one can use an optical laser to manipulate the diamond crystal lattice constant to control the crystal reflectivity and transmission. It has been shown that a 9 MeV focused boron beam can create a buried layer, approximately 5 microns below surface, with a boron concentration up to 10²¹ atoms/cm³. Here, we present simulations showing that absorbing laser pulses by a buried layer under the crystal surface would allow creating a transient temperature profile which would be well suited for the ’Q switching’ scheme.

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reference for this paper ※ https://doi.org/10.18429/JACoW-FEL2019-TUP033

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paper received ※ 21 August 2019 paper accepted ※ 29 August 2019 issue date ※ 05 November 2019

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TUP036

A Waveguide-Based High Efficiency Super-Radiant FEL Operating in the THz Regime

GUI, radiation, electron, undulator

127

P. Musumeci, A.C. Fisher
UCLA, Los Angeles, California, USA
A. Gover
University of Tel-Aviv, Faculty of Engineering, Tel-Aviv, Israel
E.A. Nanni, E.J. Snively
SLAC, Menlo Park, California, USA
S.B. van der Geer
Pulsar Physics, Eindhoven, The Netherlands

Funding: DOE grant No. DE-SC0009914 and NSF grant PHY-1734215
In this paper we describe a novel self-consistent 3D simulation approach for a waveguide FEL operating in the zero-slippage regime to generate high power THz radiation. In this interaction regime, the phase and group velocity of the radiation are matched to the relativistic beam traveling in the undulator achieving long interaction lengths. Our numerical approach is based on expanding the existing 3D particle tracking code GPT (General Particle Tracer) to follow the interaction of the particles in the beam with the electromagnetic field modes of the waveguide. We present two separate studies: one for a case which was benchmarked with experimental results and another one for a test case where, using a longer undulator and larger bunch charge, a sizable fraction of the input beam energy can be extracted and converted to THz radiation. The model presented here is an important step in the development of the zero-slippage FEL scheme as a source for high average and peak power THz radiation.

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reference for this paper ※ https://doi.org/10.18429/JACoW-FEL2019-TUP036

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paper received ※ 20 August 2019 paper accepted ※ 29 August 2019 issue date ※ 05 November 2019

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TUP038

Axial Symmetry in Spontaneous Undulator Radiation for XFELO Two-Bunch Experiment

electron, experiment, laser, radiation

134

Y.S. Li
University of Chicago, Chicago, Illinois, USA
K. Kim, R.R. Lindberg
ANL, Lemont, Illinois, USA

Funding: U.S. DOE, Office of Science, Office of BES, under Contract No. DE-AC02-06CH11357 and National Science Foundation under Award No. PHY-1549132, the Center for Bright Beams.
A well known discrepancy exists between 2D and 3D FEL simulation codes with respect to the radiation field intensity prior to the exponential gain regime [1]. This can be qualitatively explained by the fact that the 3D field representation preserves many more modes than does the axisymmetric field solved for by a 2D code. In this paper, we seek to develop an analytical model that quantifies this difference. We begin by expanding the spontaneous undulator radiation field as a multipole series, whose lowest order mode is axisymmetric. This allows us to calculate the difference in predicted intensity. Next, we confirm these results with numerical calculation and existing FEL codes GINGER and GENESIS. Finally, we discuss the implications of this study with respect to the XFELO two-bunch experiment to be conducted at LCLS-II.
[1] Z. Huang and K.-J. Kim, "Review of X-ray free-electron laser theory", Phys. Rev. ST-AB, vol. 10, p. 034801, 2007.

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reference for this paper ※ https://doi.org/10.18429/JACoW-FEL2019-TUP038

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paper received ※ 19 August 2019 paper accepted ※ 28 August 2019 issue date ※ 05 November 2019

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TUP041

X-cos SCILAB Model for Simulation of Intensity and Gain of Planar Undulator Radiation

undulator, simulation, electron, radiation

138

H. Jeevakhan
NITTTR, Bhopal, India
G. Mishra
Devi Ahilya University, Indore, India

SCILAB X-cos based model has been designed to simulate the Intensity and Gain of planar undulator radiation. Numerical approach has been used to determine the trajectories of an electron along x and z direction, traversing through a planar undulator. The present paper describes the technical details of the different blocks, parameters and possibility of combined model used for trajectory and intensity simulation Results are compared with the previous conventional syntax based codes.

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reference for this paper ※ https://doi.org/10.18429/JACoW-FEL2019-TUP041

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paper received ※ 01 August 2019 paper accepted ※ 27 August 2019 issue date ※ 05 November 2019

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TUP042

Analysis of Undulator Radiations With Asymmetric Beam and Non-Periodic Magnetic Field

undulator, electron, radiation, resonance

141

H. Jeevakhan
NITTTR, Bhopal, India
G. Mishra
Devi Ahilya University, Indore, India

Harmonic Undulator radiations at third harmonics with non periodic constant magnetic field has been analysed. Symmetric and asymmetric electron beam with homogeneous spread has been used to present viable solution for the resonance shift inherited in undulator with constant magnetic field. The radiation recovers shifts in resonance and regain its intensity with asymmetric electron beam and harmonic field
Harmonic undulator, energy spread

Poster TUP042 [2.886 MB]

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reference for this paper ※ https://doi.org/10.18429/JACoW-FEL2019-TUP042

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paper received ※ 01 August 2019 paper accepted ※ 31 October 2019 issue date ※ 05 November 2019

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TUP047

An Analysis of Optimal Initial Detuning for Maximum Energy-Extraction Efficiency

electron, extraction, synchrotron, undulator

145

Q.K. Jia
USTC/NSRL, Hefei, Anhui, People’s Republic of China

For low gain free electron laser (FEL), the phase space evolutions of trapped electrons in the phase bucket are analyzed through calculating their synchrotron oscillation periods, which vary with the initial detuning and initial phase. The optimal initial detuning for the maximum energy-extraction efficiency and the corresponding saturation length are given. The analysis demonstrated that for the low gain case the gain of the strong optical field is about a quarter of that of the weak optical field (small signal gain), and the saturation power larger than that of high gain FEL can be achieved in the resonator of oscillator FEL.

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reference for this paper ※ https://doi.org/10.18429/JACoW-FEL2019-TUP047

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paper received ※ 19 August 2019 paper accepted ※ 27 August 2019 issue date ※ 05 November 2019

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TUP049

Simulating Shot-Noise of ’Real’ Electron Bunches

micro-particles, electron, simulation, bunching

149

P. Traczykowski, L.T. Campbell, B.W.J. MᶜNeil
USTRAT/SUPA, Glasgow, United Kingdom
L.T. Campbell, B.W.J. MᶜNeil, P. Traczykowski
Cockcroft Institute, Warrington, Cheshire, United Kingdom
L.T. Campbell, P. Traczykowski
STFC/DL/ASTeC, Daresbury, Warrington, Cheshire, United Kingdom

An algorithm and numerical code for the up-sampling of a system of particles, from a smaller to a larger number, is described. The method introduces a Poissonian ’shot-noise’ to the up-sampled distribution [1], typical of the noise statistics arising in a bunch of particles generated by a particle accelerator. The algorithm is applied on a phase-space distribution of relatively few simulation particles representing an electron beam generated by particle accelerator modelling software, for subsequent injection into an Free Electron Laser (FEL) amplifier which is used here to describe the model. A much larger number of particles is usually required to model the FEL lasing process than is required in the simulation models of the electron beam accelerators that drive it. A numerical code developed from the algorithm was then used to generate electron bunches for injection into to an unaveraged 3D FEL simulation code, Puffin [2]. Results show good qualitative and quantitative agreement with analytical theory. The program and usage manual is available to download from GitHub [3].
[1] B.W.J. McNeil, M.W. Poole and G.R.M. Robb, Physical Review Special Topics - Accelerators and Beams Vol 6, 070701 (2003).
[2] L.T. Campbell and B.W.J. McNeil, Phys. Plasmas 19, 093119 (2012).
[3] https://github.com/UKFELs/JDF

Poster TUP049 [1.419 MB]

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reference for this paper ※ https://doi.org/10.18429/JACoW-FEL2019-TUP049

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paper received ※ 20 August 2019 paper accepted ※ 27 August 2019 issue date ※ 05 November 2019

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TUP050

Comparison Between, and Validation Against an Experiment of, a Slowly-varying Envelope Approximation Code and a Particle-in-Cell Simulation Code for Free-Electron Lasers

undulator, simulation, experiment, electron

153

P. Traczykowski, L.T. Campbell, J. Henderson, B.W.J. MᶜNeil
USTRAT/SUPA, Glasgow, United Kingdom
L.T. Campbell, J. Henderson, P. Traczykowski
STFC/DL/ASTeC, Daresbury, Warrington, Cheshire, United Kingdom
H. Freund
University of New Mexico, Albuquerque, USA
B.W.J. MᶜNeil, P. Traczykowski
Cockcroft Institute, Warrington, Cheshire, United Kingdom
P.J.M. van der Slot
Mesa+, Enschede, The Netherlands

Free-electron laser simulation codes employ either the Slowly-Varying Envelope Approximation (SVEA) or a Particle-in-Cell (PiC) formulation. Maxwell’s equations are averaged over the fast time scale in the SVEA so that there is no need to resolve the wave period. In contrast, the fast oscillation is retained in PiC codes. As a result, the SVEA codes are much less computationally intensive and are used more frequently than PiC codes. While the orbit dynamics in PiC codes and some SVEA Codes (MEDUSA and MINERVA) use the full unaveraged Lorentz force equations, some SVEA codes use the Kroll-Morton-Rosenbluth (KMR) approximation (GENESIS, GINGER, FAST, and TDA3D). Steady-state simulation comparisons [1] have appeared in the literature between different codes using the averaged and unaveraged particle dynamics. Recently, a comparison between three KMR SVEA codes (GENESIS, GINGER, and FAST) and the PUFFIN PiC code in the time-dependent regime has been reported [2]. In this paper, we present a comparison between the unaveraged PiC code PUFFIN, the unaveraged SVEA code MINERVA for the time-dependent simulation of SASE free-electron lasers with the experimental measurements from SPARC SASE FEL at ENEA Frascati.
[1] S.G. Biedron et al., NIMA 445, 110 (2000).
[2] B. Garcia et al., paper presented at the 38th International Free Electron Laser Conference, Santa Fe, New Mexico, 20 - 25 August 2017.

Poster TUP050 [0.908 MB]

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reference for this paper ※ https://doi.org/10.18429/JACoW-FEL2019-TUP050

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paper received ※ 02 August 2019 paper accepted ※ 28 August 2019 issue date ※ 05 November 2019

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TUP051

Plasma Accelerator Driven Coherent Spontaneous Emission

electron, radiation, bunching, undulator

157

B.M. Alotaibi, R. Altuijri
PNU, Riyadh, Kingdom of Saudi Arabia
B.M. Alotaibi, R. Altuijri, A.F. Habib, B. Hidding, B.W.J. MᶜNeil, P. Traczykowski
USTRAT/SUPA, Glasgow, United Kingdom
A.F. Habib, B. Hidding, B.W.J. MᶜNeil, P. Traczykowski
Cockcroft Institute, Warrington, Cheshire, United Kingdom

Plasma accelerators [1] are a potentially important source of high energy, low emittance electron beams with high peak currents generated within a relatively short distance. As such, they may have an important application in the driving of coherent light sources such as the Free Electron Laser (FEL) which operate into the X-ray region [2]. While novel plasma photocathodes [3] may offer orders of magnitude improvement to the normalized emittance and brightness of electron beams compared to Radio Frequency-driven accelerators, a substantial challenge is the energy spread and chirp of beams, which can make FEL operation impossible. In this paper it is shown that such an energy-chirped, ultrahigh brightness electron beam, with dynamically evolving current profile due to ballistic bunching at moderate energies, can generate significant coherent radiation output via the process of Coherent Spontaneous Emission (CSE)[4]. While this CSE is seen to cause some FEL-induced electron bunching at the radiation wavelength, the dynamic evolution of the energy chirped pulse dampens out any high-gain FEL interaction.
[1] E. Esary et al., Reviews of Modern Physics p. 1229 (2009).
[2] B. W. J. McNeil and N. R. Thompson, 2010 Nat. Photon.4 814-21
[3] B. Hidding et al., 2012 Phys. Rev. Lett. 108 035001
[4] L. T. Campbell and B. W. J. McNeil, 2012, in Proc. FEL2012

Poster TUP051 [1.401 MB]

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reference for this paper ※ https://doi.org/10.18429/JACoW-FEL2019-TUP051

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paper received ※ 20 August 2019 paper accepted ※ 27 August 2019 issue date ※ 05 November 2019

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TUP053

An Investigation of Possible Non-Standard Photon Statistics in a Free-Electron Laser I: Experiment

photon, experiment, cavity, radiation

161

J.-W. Park
University of Hawaii, Honolulu,, USA
K.-J. Kim, R.R. Lindberg
ANL, Lemont, Illinois, USA

Funding: Work supported by U.S. DOE, Office of Science, Office of BES, under Award No. DE-SC0018428.
It was reported that the photon statistics of the seventh coherent spontaneous harmonic radiation of the MARK III FEL was sub-Poissonian [1], which concludes that Fano factor F (the ratio of photon number variance to the average photon number) is less than unity. Whether FEL light exhibits such non-standard behavior is an important issue; if it does, our understanding of the FEL needs to be radically modified. In this paper, we re-examine the analyses of experimental data in Ref. [1]. We find that the observed value of F could be explained within the standard FEL theory if one combines the detector dead time effect with photon clustering arising from the FEL gain. We propose an improved experiment for a more definitive measurement of the FEL photon statistics.
[1] T. Chen and J.M. Madey, J. Phys. Rev. Lett. 86, 5906 (2001).

Poster TUP053 [0.929 MB]

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reference for this paper ※ https://doi.org/10.18429/JACoW-FEL2019-TUP053

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paper received ※ 21 August 2019 paper accepted ※ 12 September 2019 issue date ※ 05 November 2019

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TUP054

An Investigation of Possible Non-Standard Photon Statistics in a Free-Electron Laser II: Theory

electron, photon, radiation, laser

165

J.-W. Park
University of Hawaii, Honolulu,, USA
K.-J. Kim, R.R. Lindberg
ANL, Lemont, Illinois, USA
K.-J. Kim
University of Chicago, Chicago, Illinois, USA

Funding: Work supported by U.S. DOE, Office of Science, Office of BES, under Award No. DE-SC0018428.
In this paper we explore whether we can at present find a theoretical basis for non-standard, sub-Poissonian photon statistics in the coherent spontaneous harmonic radiation of an FEL as was claimed to have been measured with the Mark III FEL [1]. We develop a one dimensional quantum FEL oscillator model of the harmonic radiation in the linear gain regime to calculate the photon statistics. According to our study, it seems unlikely that the photon statistics for an FEL oscillator starting from the noise could be sub-Poissonian.
[1] T. Chen and J.M. Madey, J. Phys. Rev. Lett. 86, 5906 (2001).

Poster TUP054 [0.386 MB]

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reference for this paper ※ https://doi.org/10.18429/JACoW-FEL2019-TUP054

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paper received ※ 21 August 2019 paper accepted ※ 16 September 2019 issue date ※ 05 November 2019

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TUP055

Two-Color Operation of FLASH2 Undulator

undulator, electron, laser, operation

168

E. Schneidmiller, M. Braune, B. Faatz, U. Jastrow, M. Kuhlmann, A.A. Sorokin, K.I. Tiedtke, M.V. Yurkov
DESY, Hamburg, Germany

FLASH is the first soft X-ray FEL user facility, routinely providing brilliant photon beams for users since 2005. The second undulator branch of this facility, FLASH2, is gap-tunable which allows to test and use advanced lasing concepts. In particular, we tested recently a two-color mode of operation based on the alternation of tunes of the undulator segments (every other segment is tuned to the second wavelength). This scheme is advantageous in comparison with a subsequent generation of two colors in two different parts of the undulator. First, source positions of two FEL beams are close to each other which makes it easier to handle them. Second, the amplification is more efficient in this configuration since the segments with respectively "wrong" wavelength act as bunchers. We developed methods for online intensity measurements of the two colors simultaneously that require a combination of two detectors. We present some examples of such measurements in the XUV and soft X-ray regimes.

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reference for this paper ※ https://doi.org/10.18429/JACoW-FEL2019-TUP055

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paper received ※ 20 August 2019 paper accepted ※ 28 August 2019 issue date ※ 05 November 2019

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TUP056

Feasibility Studies of the 100 keV Undulator Line of the European XFEL

undulator, electron, photon, laser

172

E. Schneidmiller, V. Balandin, W. Decking, M. Dohlus, N. Golubeva, D. Nölle, M.V. Yurkov, I. Zagorodnov
DESY, Hamburg, Germany
G. Geloni, Y. Li, S. Molodtsov, J. Pflüger, S. Serkez, H. Sinn, T. Tanikawa, S. Tomin
EuXFEL, Schenefeld, Germany

The European XFEL is a multi-user X-ray FEL facility based on superconducting linear accelerator. Presently, three undulators (SASE1, SASE2, SASE3) deliver high-brightness soft- and hard- X-ray beams for users. There are two empty undulator tunnels that were originally designed to operate with spontaneous radiators. We consider instead a possible installation of two FEL undulators. One of them (SASE4) is proposed for the operation in ultrahard X-ray regime, up to the photon energy of 100 keV. In this contribution we present the results of the first feasibility studies of this option.

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reference for this paper ※ https://doi.org/10.18429/JACoW-FEL2019-TUP056

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paper received ※ 20 August 2019 paper accepted ※ 27 August 2019 issue date ※ 05 November 2019

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TUP057

Analysis of Parameter Space of Soft X-Ray Free Electron Laser at the European XFEL Driven by High and Low Energy Electron Beam

undulator, electron, radiation, operation

176

E. Schneidmiller, M.V. Yurkov
DESY, Hamburg, Germany

Three undulator beamlines: SASE1 and SASE2 (hard X-ray), and SASE3 (soft X-ray) are in operation at the European XFEL serving six user instruments. Next stages of the facility development are installation of two undulator beamlines in empty tunnels SASE4 and SASE5 as medium term upgrade, and extension of the facility with the second fan of undulators as long term upgrade. Construction of soft X-ray beamlines is considered in both upgrade scenario. In the case of SASE4/SASE5 electron beam with energies 8.5 GeV - 17.5 GeV will be used in order to provide simultaneous operation of new undulator beamlines with existing SASE1-SASE3. One of the scenarios for a second fan of undulators involves using of low energy (2.5 GeV) electron beam. In this paper we analyze parameter space of soft X-ray SASE FELs driven by high energy and low energy electron beam, compare output characteristics, and discuss potential advantages and disadvantages.

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reference for this paper ※ https://doi.org/10.18429/JACoW-FEL2019-TUP057

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paper received ※ 20 August 2019 paper accepted ※ 27 August 2019 issue date ※ 05 November 2019

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TUP058

First Characterization of the Photon Beam at the European XFEL in July, 2017

radiation, photon, electron, undulator

180

V. Balandin, B. Beutner, F. Brinker, W. Decking, M. Dohlus, L. Fröhlich, U. Jastrow, R. Kammering, T. Limberg, D. Nölle, M. Scholz, A.A. Sorokin, K.I. Tiedtke, M.V. Yurkov, I. Zagorodnov
DESY, Hamburg, Germany
U. Boesenberg, W. Freund, J. Grünert, A. Koch, N.G. Kujala, J. Liu, Th. Maltezopoulos, M. Messerschmidt, I. Petrov, L. Samoylova, H. Sinn
EuXFEL, Schenefeld, Germany

North branch of the European XFEL, SASE1, produced first light on May 3rd, 2017, and XFEL operation has been gradually improved then. First characterization of the photon beam has been performed in July / August 2017, just before an official starting date of user experiments (September 1st, 2017). Energy of the electron beam was 14 GeV, bunch charge was 500 pC, photon energy was 9.3 keV. With photon diagnostics available at that time (X-ray gas monitor (XGM) and FEL imager) we measured the gain curve and traced evolution of the FEL radiation mode along the undulator. An important conclusion is that experimental results demonstrate reasonable agreement with baseline parameters. Developed techniques of the photon beam characterization also provided solid base for identification of the problems and means for improving SASE FEL tuning and operation.

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reference for this paper ※ https://doi.org/10.18429/JACoW-FEL2019-TUP058

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paper received ※ 20 August 2019 paper accepted ※ 27 August 2019 issue date ※ 05 November 2019

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TUP059

Influence of Energy Chirp in the Electron Beam and Undulator Tapering on Spatial Properties of the Radiation From Seeded and SASE FEL

undulator, radiation, electron, laser

184

E. Schneidmiller, M.V. Yurkov
DESY, Hamburg, Germany

Energy chirp and undulator tapering change resonance condition along the electron beam and undulator which results in modification of the radiation amplification process. Well known examples are post-saturation undulator tapering for radiation power increase, reverse undulator tapering for effective operation of afterburners, and application of linear undulator tapering for compensation of energy chirp effect. These are essentially one dimensional effects. In addition, energy chirp and undulator tapering also change spatial properties of the radiation which can be important for the users of X-ray FEL facilities. In this report we present detailed analysis of the spatial properties of the radiation from an FEL amplifier with tapered undulator and chirped electron beam. Two configurations, seeded FEL amplifier, and SASE FEL are under consideration. Dependence of the spatial distributions on the electron beam properties is studied, and their evolution along the undulator is traced. It is shown that spatial properties of the radiation may be significantly distorted by the effects of energy chirp in the electron beam and undulator tapering.

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reference for this paper ※ https://doi.org/10.18429/JACoW-FEL2019-TUP059

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paper received ※ 24 August 2019 paper accepted ※ 28 August 2019 issue date ※ 05 November 2019

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TUP060

An Advanced Compression Option for the European XFEL

electron, undulator, laser, photon

187

I. Zagorodnov, M. Dohlus, E. Schneidmiller, M.V. Yurkov
DESY, Hamburg, Germany

An advanced compression scheme which allows to obtain a high peak current while preserving the low slice emittance is considered. The beam is compressed weakly in the bunch compressors and the current is increased by eSASE setup at the entrance of the undulator line. It is shown by numerical studies that such approach allows to reduce harmful collective effects in the bunch compressors and in the transport line. Simulations of FEL physics confirm the possibility to obtain a high level of SASE radiation at the ultra-hard photon energy level of 100 keV.

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reference for this paper ※ https://doi.org/10.18429/JACoW-FEL2019-TUP060

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paper received ※ 19 August 2019 paper accepted ※ 25 August 2019 issue date ※ 05 November 2019

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TUP061

Super-X: Simulations for Extremely Hard X-Ray Generation With Short Period Superconducting Undulators for the European XFEL

undulator, electron, photon, simulation

191

S. Serkez, G. Geloni, S. Karabekyan, Y. Li, T. Tanikawa, S. Tomin, F. Wolff-Fabris
EuXFEL, Schenefeld, Germany
C. Boffo
Bilfinger Noell GmbH, Wuerzburg, Germany
S. Casalbuoni
KIT, Eggenstein-Leopoldshafen, Germany
M. Dohlus, E. Schneidmiller, M.V. Yurkov, I. Zagorodnov
DESY, Hamburg, Germany
A. Trebushinin
BINP, Novosibirsk, Russia

The European XFEL is a high-repetition multi-user facility with nominal photon energy range covering almost 3 orders of magnitude: 250 eV - 25 keV. In this work we explore the possibility to extend the photon energy range of the facility up to 100 keV via combination of superconducting undulator technology, period doubling and harmonic lasing, thus allowing for excellent tunability. To this purpose, we propose a dedicated FEL line, discuss its overall concept and provide analytical and numerical estimations of its expected performance.

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reference for this paper ※ https://doi.org/10.18429/JACoW-FEL2019-TUP061

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paper received ※ 20 August 2019 paper accepted ※ 25 August 2019 issue date ※ 05 November 2019

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TUP062

Two Colors at the SASE3 Line of the European XFEL: Project Scope and First Measurements

electron, photon, experiment, radiation

195

S. Serkez, G. Geloni, N. Gerasimova, J. Grünert, S. Karabekyan, A. Koch, J. Laksman, Th. Maltezopoulos, T. Mazza, M. Meyer, S. Tomin
EuXFEL, Schenefeld, Germany
W. Decking, L. Fröhlich, V. Kocharyan, Y.A. Kot, E. Saldin, E. Schneidmiller, M. Scholz, M.V. Yurkov, I. Zagorodnov
DESY, Hamburg, Germany
M. Huttula
University of Oulu, Oulu, Finland
E. Kukk
University of Turku, Turku, Finland

The European XFEL is a high-repetition rate facility that generates high-power SASE radiation pulses in three beamlines. A joint upgrade project, with Finnish universities, to equip the SASE3 beamline with a chicane has been recently approved to generate two SASE pulses with different photon energies and temporal separation. In this work we report the status of the project, its expected performance, and recent experimental results. Additionally, we discuss methods to diagnose the properties of the generated radiation.

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reference for this paper ※ https://doi.org/10.18429/JACoW-FEL2019-TUP062

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paper received ※ 20 August 2019 paper accepted ※ 29 August 2019 issue date ※ 05 November 2019

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TUP063

Physical Design and FEL Performance Study for FEL-III Beamline of SHINE

undulator, wakefield, photon, electron

199

N. Huang
SINAP, Shanghai, People’s Republic of China
H.X. Deng, B. Liu, D. Wang
SARI-CAS, Pudong, Shanghai, People’s Republic of China

The first hard X-ray free electron laser (XFEL) facility in China, the Shanghai High-Repetition-Rate XFEL and Extreme Light Facility (SHINE), is under construction, which allows for generating X-ray pulses in the photon energy range from 3 keV to 25 keV. To produce X-ray pulses with photon energy up to 25 keV, FEL-III undulator line of SHINE employs superconducting undulators. However, the smaller gap of the superconducting undulator poses serious wakefield effect reducing the FEL power, compared to the normal planar undulator. For a setup design optimization, the design and performance of the FEL-III undulator line are presented using start-to-end beam simulations at self-amplified spontaneous emission (SASE) and self-seeding mode. The wakefield impact on FEL performance is then investigated. A linear undulator tapering technique is adopted for recovering the FEL power to the non-wakefield level.

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reference for this paper ※ https://doi.org/10.18429/JACoW-FEL2019-TUP063

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paper received ※ 19 August 2019 paper accepted ※ 28 August 2019 issue date ※ 05 November 2019

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TUP064

Effect on FEL Gain Curve Using Phase Shifters

electron, undulator, laser, simulation

203

M.H. Cho, H.-S. Kang, G. Kim, C.H. Shim, H. Yang
PAL, Pohang, Republic of Korea

Phase matching between FEL and electron beam should be precisely controlled for FEL amplification. Phase shifters located between undulators performs the phase matching. An electron beam can be controlled to be in the in- or out-phase by setting the phase shifters from the phase shifter scan. In this article, we show effects of FEL gain curve by setting the in- and out-phase of electron beam. We address reasons of the reduction of FEL intensity in the out-phase condition dividing the linear and saturation FEL amplification regimes. In the linear regime the gain curve is shifted, and in the saturation regime the electron loss occurs during the undulator tapering. Our results show agreements with experiments performed at PAL-XFEL.

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reference for this paper ※ https://doi.org/10.18429/JACoW-FEL2019-TUP064

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paper received ※ 21 August 2019 paper accepted ※ 28 August 2019 issue date ※ 05 November 2019

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TUP065

Optimization of a Coherent Undulator Beamline for New Advanced Synchrotron Light Source in Korea

undulator, electron, synchrotron, radiation

206

I.G. Jeong, P. Buaphad, Y.J. Joo, Y. Kim, H.R. Lee
University of Science and Technology of Korea (UST), Daejeon, Republic of Korea
P. Buaphad, Y.J. Joo, Y. Kim, H.R. Lee
KAERI, Jeongeup-si, Republic of Korea
M.Y. Han, I.G. Jeong, J.Y. Lee, S.H. Lee
Korea Atomic Energy Research Institute (KAERI), Daejeon, Republic of Korea

Recently, the demand for a new advanced synchrotron light source in Korea is rapidly growing. Six local governments in Korea would like to host the new synchrotron light source project in their own provinces. The new advanced synchrotron light source will be the Diffraction-Limited Storage Ring (DLSR), which is based on the Multi-Bend Achromat (MBA) lattice. For the new synchrotron light source, we would like to build a special 60-m long coherent undulator beamline, which can deliver high-intensity coherent radiation at the hard X-ray region. To design the coherent undulator beamline, we have performed numerous beam dynamics simulations with GENESIS and SIMPLEX codes. In this paper, we report design concepts and those simulation results for the coherent undulator beamline.

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reference for this paper ※ https://doi.org/10.18429/JACoW-FEL2019-TUP065

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paper received ※ 26 August 2019 paper accepted ※ 26 August 2019 issue date ※ 05 November 2019

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TUP066

Start-to-End Simulations for the Soft X-Ray FEL at the MAX IV Laboratory

simulation, electron, linac, undulator

210

W. Qin, J. Andersson, F. Curbis, L. Isaksson, M. Kotur, E. Mansten, M.A. Pop, S. Thorin, S. Werin
MAX IV Laboratory, Lund University, Lund, Sweden
F. Curbis, S. Werin
SLF, Lund, Sweden

Funding: The work is supported by Knut and Alice Wallenberg foundation.
A Soft X-ray FEL (the SXL) using the existing 3 GeV linac at the MAX IV Laboratory is currently in the design phase. In this contribution, start-to-end simulations, including the photo-injector simulations using ASTRA, the linac simulations using ELEGANT and the FEL simulations using GENESIS, are presented for 100 pC and 10 pC operation modes. The features of the electron beam from the MAX IV linac and their impact on the FEL performance are discussed.

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reference for this paper ※ https://doi.org/10.18429/JACoW-FEL2019-TUP066

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paper received ※ 20 August 2019 paper accepted ※ 28 August 2019 issue date ※ 05 November 2019

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TUP067

Advanced Concepts in the Design for the Soft X-Ray FEL at MAX IV

undulator, electron, laser, brightness

214

W. Qin, F. Curbis, M.A. Pop, S. Werin
MAX IV Laboratory, Lund University, Lund, Sweden
F. Curbis, S. Werin
SLF, Lund, Sweden

Funding: The work is supported by Knut and Alice Wallenberg foundation.
A Soft X-ray FEL (the SXL) is currently being designed at the MAX IV Laboratory. In the work to adapt the FEL to the scientific cases several advanced options are being studied for coherence enhancement, generation of short pulses and two-color pulses. We will discuss the current status and the schemes studied, especially regarding the FEL performance with the features of the MAX IV linac, including a positive energy chirp.

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reference for this paper ※ https://doi.org/10.18429/JACoW-FEL2019-TUP067

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paper received ※ 20 August 2019 paper accepted ※ 29 August 2019 issue date ※ 05 November 2019

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TUP072

Orbital Angular Momentum from SASE

electron, quadrupole, radiation, undulator

218

J.F. Morgan, B.W.J. MᶜNeil
USTRAT/SUPA, Glasgow, United Kingdom
B.W.J. MᶜNeil, J.F. Morgan, B.D. Muratori, P.H. Williams, A. Wolski
Cockcroft Institute, Warrington, Cheshire, United Kingdom
B.D. Muratori, P.H. Williams
STFC/DL/ASTeC, Daresbury, Warrington, Cheshire, United Kingdom
A. Wolski
The University of Liverpool, Liverpool, United Kingdom

Radiation with orbital angular momentum, OAM, has many applications such as in imaging systems and microscopic tweezers [1]. The feasibility of generating light with OAM in a free electron laser, FEL, from amplified shot noise in an electron beam is investigated using the FEL simulation code Puffin [2]. This may allow generation of OAM radiation at shorter wavelengths than currently available, as well as the opportunity to incorporate the technique with other SASE manipulation schemes such as mode locking [3].
[1] A. M. Yao and M. J. Padgett, Adv. Opt. Photon. 3, 161(2011)
[2] L. T. Campbell and B. W. J. McNeil, Phys. Plasmas. 19, 093119(2012)
[3] D. J. Dunning, B. W. J. McNeil, and N. R. Thompson, Phys. Rev. Lett. 110, 104801(2013)

Poster TUP072 [1.311 MB]

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reference for this paper ※ https://doi.org/10.18429/JACoW-FEL2019-TUP072

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paper received ※ 20 August 2019 paper accepted ※ 28 August 2019 issue date ※ 05 November 2019

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TUP073

High-Repetition-Rate Seeding Schemes Using a Resonator-Amplifier Setup

laser, electron, radiation, cavity

222

S. Ackermann, B. Faatz, V. Grattoni, C. Lechner, G. Paraskaki
DESY, Hamburg, Germany
G. Geloni, S. Serkez, T. Tanikawa
EuXFEL, Schenefeld, Germany
W. Hillert
University of Hamburg, Institut für Experimentalphysik, Hamburg, Germany

The spectral and temporal properties of Free-Electron Lasers (FEL) operating on the basis of self-amplified spontaneous emission (SASE) suffer from the stochastic behavior of the start-up process. Several so-called "seeding"-techniques using external radiation fields to overcome this limitation have been proposed and demonstrated. The external seed is usually generated by demanding, high-power laser systems, which are not available with a sufficient laser pulse energy at the high repetition rates of superconducting FEL facilities. In this contribution we discuss several seeding schemes that lower the requirements for the used laser systems, enabling seeded operation at high repetition rates by the means of a resonator-amplifier setup.

Poster TUP073 [0.521 MB]

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reference for this paper ※ https://doi.org/10.18429/JACoW-FEL2019-TUP073

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paper received ※ 06 August 2019 paper accepted ※ 29 August 2019 issue date ※ 05 November 2019

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TUP074

FLASH Upgrade for Seeding

laser, undulator, simulation, electron

226

V. Grattoni, S. Ackermann, B. Faatz, T. Lang, C. Lechner, M.M. Mohammad Kazemi, G. Paraskaki
DESY, Hamburg, Germany
W. Hillert
University of Hamburg, Institut für Experimentalphysik, Hamburg, Germany

An upgrade for FLASH, the SASE FEL in Hamburg, is planned after 2020 aiming at fulfilling user requirements like fully coherent, variable polarization, and multi-colour pulses. In this proceeding, we focus on the FLASH1 beamline that will be operated in seeded mode at a high repetition rate. In particular, we will present and discuss the proposed seeding schemes for delivering FEL radiation with wavelengths from 60 down to 4 nm

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reference for this paper ※ https://doi.org/10.18429/JACoW-FEL2019-TUP074

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paper received ※ 19 August 2019 paper accepted ※ 28 August 2019 issue date ※ 05 November 2019

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TUP076

Seeding R&D at sFLASH

electron, laser, free-electron-laser, experiment

230

C. Lechner, S. Ackermann, R.W. Aßmann, B. Faatz, V. Grattoni, I. Hartl, S.D. Hartwell, R. Ivanov, T. Laarmann, T. Lang, M.M. Mohammad Kazemi, G. Paraskaki, A. Przystawik, J. Zheng
DESY, Hamburg, Germany
A. Azima, H. Biss, M. Drescher, W. Hillert, V. Miltchev, J. Roßbach
University of Hamburg, Institut für Experimentalphysik, Hamburg, Germany
S. Khan
DELTA, Dortmund, Germany

Funding: Work supported by Federal Ministry of Education and Research of Germany under contract No. 05K13GU4, 05K13PE3, and 05K16PEA.
Free-electron lasers (FELs) based on the self-amplified spontaneous emission (SASE) principle generate photon pulses with typically poor longitudinal coherence. FEL seeding techniques greatly improve longitudinal coherence by initiating FEL amplification in a controlled way using coherent light pulses. The sFLASH experiment installed at the FEL user facility FLASH at DESY in Hamburg is dedicated to the study of external seeding techniques. In this paper, the layout of the sFLASH seeding experiment is presented and an overview of recent developments is given.

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reference for this paper ※ https://doi.org/10.18429/JACoW-FEL2019-TUP076

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paper received ※ 30 September 2019 paper accepted ※ 17 October 2019 issue date ※ 05 November 2019

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TUP077

Study of a Seeded Oscillator-Amplifier FEL

laser, electron, simulation, free-electron-laser

234

G. Paraskaki, S. Ackermann, B. Faatz, V. Grattoni, C. Lechner, M. Mehrjoo
DESY, Hamburg, Germany
G. Geloni, S. Serkez, T. Tanikawa
EuXFEL, Schenefeld, Germany
W. Hillert
University of Hamburg, Institut für Experimentalphysik, Hamburg, Germany

In recent years, there is interest of the Free-Electron Laser (FEL) community in external-seeding techniques such as the Echo-Enabled Harmonic Generation (EEHG) and the High-Gain Harmonic Generation (HGHG). With these techniques, pulses of an improved temporal coherence are generated, but at the same time, they are limited by the repetition rates that seed lasers can currently offer with the required pulse energies. A big challenge is to combine the advantages of seeding schemes with high repetition rates. For this purpose, we study a combination of an oscillator-amplifier. The modulator in the oscillator is used at a long wavelength to modulate the electron beam and an amplifier is operated to extract the FEL radiation of the desired harmonic. This way we can use a seed laser of 10 Hz in a burst mode and a resonator to feedback the radiation at repetition rates of superconducting accelerators instead of using an external seed at these high-repetition rates. In this contribution, we present simulation results of a seeded oscillator-amplifier FEL in an HGHG scheme.

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reference for this paper ※ https://doi.org/10.18429/JACoW-FEL2019-TUP077

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paper received ※ 19 August 2019 paper accepted ※ 29 August 2019 issue date ※ 05 November 2019

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TUP078

Impact of Electron Beam Energy Chirp on Seeded FELs

electron, laser, simulation, timing

238

G. Paraskaki, S. Ackermann, B. Faatz, V. Grattoni, C. Lechner, J. Zemella
DESY, Hamburg, Germany
W. Hillert
University of Hamburg, Institut für Experimentalphysik, Hamburg, Germany

Seeded FELs enable the generation of fully coherent, transform-limited and high brightness FEL pulses, as the start-up process is driven by an external coherent light pulse. During the design process of such FELs, it is important to choose carefully the electron beam parameters to guarantee high performance. One of those parameters is the electron beam energy chirp. In this contribution, we show simulation results and we discuss how the electron beam energy chirp affects the final spectrum.

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reference for this paper ※ https://doi.org/10.18429/JACoW-FEL2019-TUP078

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paper received ※ 16 August 2019 paper accepted ※ 28 August 2019 issue date ※ 05 November 2019

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TUP079

Status of the Hard X-Ray Self-Seeding Setup at the European XFEL

undulator, electron, radiation, simulation

242

G. Geloni, S. Karabekyan, D. La Civita, L. Samoylova, S. Serkez, R. Shayduk, H. Sinn, V. Sleziona, M. Vannoni, M. Yakopov
EuXFEL, Schenefeld, Germany
J.W.J. Anton, S.P. Kearney, D. Shu
ANL, Lemont, Illinois, USA
V.D. Blank, S. Terentiev
TISNCM, Troitsk, Russia
W. Decking, V. Kocharyan, S. Liu, E. Negodin, E. Saldin, T. Wohlenberg
DESY, Hamburg, Germany
X. Dong
European X-Ray Free-Electron Laser Facility GmbH, Schelefeld, Germany

A Hard X-Ray Self-Seeding (HXRSS) setup will be soon commissioned at the European XFEL. It relies on a two-chicanes scheme to deal, in particular, with the high pulse repetition rate of the facility. In this contribution we review the physics choices made at the design stage and the expected performance of the setup. We will also focus on the description of the hardware installations made at the SASE2 line of the European XFEL.

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reference for this paper ※ https://doi.org/10.18429/JACoW-FEL2019-TUP079

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paper received ※ 27 August 2019 paper accepted ※ 28 August 2019 issue date ※ 05 November 2019

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TUP083

Energy Spread Impact on HGHG and EEHG FEL Pulse Energy

laser, electron, bunching, photon

250

S. Spampinati, E. Allaria, L. Giannessi, P. Rebernik Ribič
Elettra-Sincrotrone Trieste S.C.p.A., Basovizza, Italy
L. Giannessi
ENEA C.R. Frascati, Frascati (Roma), Italy
P. Rebernik Ribič
University of Nova Gorica, Nova Gorica, Slovenia

VUV and X-ray free electron lasers (FELs) require a very bright electron beam. Seeded FEL harmonic generation is particularly sensible to energy spread and slice energy spread can limit the highest harmonic conversion factor at which coherent radiation can be produced. Different cas-cade schemes can have different sensibility to the slice energy spread. At FERMI we have evaluated the impact of the slice energy spread on the performance of high gain harmonic generation (HGHG) and of echo enable harmonic generation (EEHG) by measuring the FEL pulse energy as function of the electron beam slice energy spread. The measurements were done at different harmon-ics. The slice energy spread was varied trough the laser heater located in the linac that drives FERMI.

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reference for this paper ※ https://doi.org/10.18429/JACoW-FEL2019-TUP083

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paper received ※ 20 August 2019 paper accepted ※ 17 September 2019 issue date ※ 05 November 2019

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TUP087

Start-to-end Simulations of the Reflection Hard X-Ray Self-Seeding at the SHINE Project

undulator, photon, simulation, electron

254

T. Liu, X. Dong, C. Feng
SARI-CAS, Pudong, Shanghai, People’s Republic of China

The Shanghai high repetition rate XFEL and extreme light Facility (SHINE) project is designed to produce fully coherent X-ray photons covering the photon energy from 3 keV to 25 keV. We have reported our FEL proposal and schemes in the hard X-ray regime which is self-seeding based on the crystal monochromator previously. Comparing to the transmission self-seeding scheme, the reflection one has several advantages and might be the base proposal. Start-to-end (S2E) simulations from the beam generation by Astra, the linac accelerating by Elegant to the FEL simulation by Genesis are performed. In this manuscript, the FEL simulations based on the S2E beam will be presented mainly. The results demonstrate the feasibility of the reflection hard X-ray self-seeding at the SHINE project.

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reference for this paper ※ https://doi.org/10.18429/JACoW-FEL2019-TUP087

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paper received ※ 20 August 2019 paper accepted ※ 29 August 2019 issue date ※ 05 November 2019

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TUP088

Numerical Simulations for Generating Fully Coherent Soft X-Ray Free Electron Lasers With Ultra-Short Wavelength

electron, laser, radiation, free-electron-laser

258

K.S. Zhou, H.X. Deng, B. Liu, D. Wang
SARI-CAS, Pudong, Shanghai, People’s Republic of China

For the fully coherent, ultra-short and high power soft X-rays are becoming key instruments in many different research fields, such as biology, chemistry or physics. However, it’s hard to generate this kind of advanced light source by the conventional lasers, especially for the soft X-rays with ultra-short wavelength because of no suitable reflectors. The external seeded free electron laser (FEL) is considered as one feasible method. Here, we give an example to generate highly temporal coherent soft X-rays with the wavelength 1 nm by the two-stage cascaded schemes. EEHG scheme is used as the first-stage while the HGHG scheme is used as the second-stage.

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reference for this paper ※ https://doi.org/10.18429/JACoW-FEL2019-TUP088

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paper received ※ 20 August 2019 paper accepted ※ 22 October 2019 issue date ※ 05 November 2019

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TUP090

Considerations on Implementing EEHG with a Strong Linear Chirp

electron, laser, simulation, bunching

262

M.A. Pop, F. Curbis, W. Qin, S. Werin
MAX IV Laboratory, Lund University, Lund, Sweden
F. Curbis, S. Werin
SLF, Lund, Sweden
W. Qin
Lund University, Lund, Sweden

Funding: The work is supported by Knut and Alice Wallenberg foundation.
The Soft X-ray Laser (SXL) currently being studied at MAX IV Laboratory is envisioned to produce coherent radiation in the 1-5 nm wavelength range. In this contribution, we present the results of simulations aimed at adding to the SXL an Echo Enabled Harmonic Generation scheme, which has been shown to increase the coherence of FELs in the Soft X-ray regime. Our work puts special emphasis on accommodating the positive energy chirp of the electron bunch coming out of the MAX IV Linac and on generating sufficient bunching at the high harmonics necessary for covering the full wavelength range.

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reference for this paper ※ https://doi.org/10.18429/JACoW-FEL2019-TUP090

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paper received ※ 20 August 2019 paper accepted ※ 28 August 2019 issue date ※ 05 November 2019

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TUP091

Start-to-End Simulation of the NSRRC Seeded VUV FEL

laser, electron, undulator, simulation

266

S.Y. Teng
NTHU, Hsinchu, Taiwan
C.H. Chen, W.K. Lau, A.P. Lee
NSRRC, Hsinchu, Taiwan

A free electron laser (FEL) driven by a high brightness electron linac system has been proposed to generate ultrashort intense coherent radiation in the vacuum ultraviolet region. It is a third harmonic high-gain high harmonic generation (HGHG) FEL for generation of VUV radiation with wavelength at 66.7 nm from a 20-mm period length helical undulator. A 200-nm seed laser is used for beam energy modulation in a 10-periods helical undulator of 24-mm period length. A small chicane is placed between the two undulators to optimize power growth in the radiator. In this study, we perform start-to-end simulation to foresee the operational performance of the test facility and preliminary results are presented.

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reference for this paper ※ https://doi.org/10.18429/JACoW-FEL2019-TUP091

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paper received ※ 20 August 2019 paper accepted ※ 28 August 2019 issue date ※ 05 November 2019

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TUP092

XFEL Third Harmonic Statistics Measurement at LCLS

photon, undulator, experiment, radiation

269

A. Halavanau, C. Emma, E. Hemsing, A.A. Lutman, G. Marcus, C. Pellegrini
SLAC, Menlo Park, California, USA

We investigate the statistical properties of the 6 keV third harmonic XFEL radiation at 2 keV fundamental photon energy at LCLS. We performed third harmonic self-seeding in the hard X-ray self-seeding chicane and characterized the attained non-linear third harmonic spectrum. We compare theoretical predictions with experimental results.

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reference for this paper ※ https://doi.org/10.18429/JACoW-FEL2019-TUP092

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paper received ※ 20 August 2019 paper accepted ※ 29 August 2019 issue date ※ 05 November 2019

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TUD02

Application of Infrared FEL Oscillators for Producing Isolated Attosecond X-Ray Pulses via High-Harmonic Generation in Rare Gases

cavity, laser, experiment, photon

272

R. Hajima, K. Kawase, R. Nagai
QST, Tokai, Japan
Y. Hayakawa, T. Sakai, Y. Sumitomo
LEBRA, Funabashi, Japan
T. Miyajima, M. Shimada
KEK, Ibaraki, Japan
H. Ohgaki, H. Zen
Kyoto University, Kyoto, Japan

Funding: Quantum Leap Flagship Program (MEXT Q-LEAP)
High harmonic generation (HHG) in rare gases is now becoming a common technology to produce attosecond pulses in VUV wavelengths. So far HHG sources have been realized by femtosecond solid-state lasers, not FELs. We propose a FEL-driven HHG source to explore attosecond pulses at photon energies above 1 keV with a MHz-repetition, which is difficult with solid-state lasers [1]. A research program has been launched to establish technologies for the FEL-HHG, which covers generation and characterization of few-cycle IR pulses in a FEL oscillator, stacking of FEL pulses in an external cavity, and a seed laser for stabilization of carrier-envelope phase in a FEL oscillator. In this talk, we present the scheme of FEL-HHG and the status of the research program.
[1] R. Hajima and R. Nagai, Phys. Rev. Lett. 119, 204802 (2017)

Slides TUD02 [8.995 MB]

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reference for this paper ※ https://doi.org/10.18429/JACoW-FEL2019-TUD02

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paper received ※ 23 August 2019 paper accepted ※ 29 August 2019 issue date ※ 05 November 2019

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TUD03

Fine and Hyperfine Structure of FEL Emission Spectra

electron, radiation, laser, experiment

276

V.V. Kubarev, Ya.V. Getmanov, O.A. Shevchenko
BINP SB RAS, Novosibirsk, Russia
S. Bae, Y.U. Jeong
KAERI, Daejon, Republic of Korea

This paper presents the results of experimental investigations of the fine and hyperfine spectral structures of the Novosibirsk free-electron laser (NovoFEL) and the compact free-electron laser of the Korea Atomic Energy Research Institute (KAERI FEL) by means of the optimal instruments, resonance Fabry-Perot interferometers. The very high coherence of the NovoFEL spectrum was measured in regimes with one pulse circulating inside its optical resonator (the coherence length is 7 km, and the relative width of the hyperfine structure lines is 2E-8) and with total absence of coherence between two circulating pulses, i.e. the fine structure. Sixty pulses circulate simultaneously inside the KAERI FEL optical resonator, and the measured coherence length on average covers ten pulses (the coherence length is 1 m; the relative width of the fine structure lines is 10^-4).

Slides TUD03 [3.177 MB]

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reference for this paper ※ https://doi.org/10.18429/JACoW-FEL2019-TUD03

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paper received ※ 16 August 2019 paper accepted ※ 29 August 2019 issue date ※ 05 November 2019

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TUD04

Cavity-Based Free-Electron Laser Research and Development: A Joint Argonne National Laboratory and SLAC National Laboratory Collaboration

electron, cavity, undulator, laser

282

G. Marcus, F.-J. Decker, G.L. Gassner, A. Halavanau, J.B. Hastings, Z. Huang, Y. Liu, J.P. MacArthur, R.A. Margraf, T.O. Raubenheimer, A. Sakdinawat, T.-F. Tan, D. Zhu
SLAC, Menlo Park, California, USA
J.W.J. Anton, L. Assoufid, K. Goetze, W.G. Jansma, S.P. Kearney, K. Kim, R.R. Lindberg, A. Miceli, X. Shi, D. Shu, Yu. Shvyd’ko, J.P. Sullivan, M. White
ANL, Lemont, Illinois, USA
B. Lantz
Stanford University, Stanford, California, USA

One solution for producing longitudinally coherent FEL pulses is to store and recirculate the output of an amplifier in an X-ray cavity so that the X-ray pulse can interact with following fresh electron bunches over many passes. The X-ray FEL oscillator (XFELO) and the X-ray regenerative amplifier FEL (XRAFEL) concepts use this technique and rely on the same fundamental ingredients to realize their full capability. Both schemes require a high repetition rate electron beam, an undulator to provide FEL gain, and an X-ray cavity to recirculate and monochromatize the radiation. The shared infrastructure, complementary performance characteristics, and potentially transformative FEL properties of the XFELO and XRAFEL have brought together a joint Argonne National Laboratory (ANL) and SLAC National Laboratory (SLAC) collaboration aimed at enabling these schemes at LCLS-II. We present plans to install a rectangular X-ray cavity in the LCLS-II undulator hall and perform experiments employing 2-bunch copper RF linac accelerated electron beams. This includes performing cavity ring-down measurements and 2-pass gain measurements for both the low-gain XFELO and the high-gain RAFEL schemes.

Slides TUD04 [12.425 MB]

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reference for this paper ※ https://doi.org/10.18429/JACoW-FEL2019-TUD04

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paper received ※ 25 August 2019 paper accepted ※ 29 August 2019 issue date ※ 05 November 2019

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TUT01

Superradiance and Stimulated-Superradiant Emission of Bunched Electron Beams

radiation, electron, wiggler, undulator

288

A. Gover, R. Ianconescu
University of Tel-Aviv, Faculty of Engineering, Tel-Aviv, Israel
C. Emma, P. Musumeci, C. Pellegrini, N.S. Sudar
UCLA, Los Angeles, USA
A. Friedman
Ariel University, Ariel, Israel
R. Ianconescu
Shenkar College of Engineering and Design, Ramat Gan, Israel

Funding: We acknowledge support of the Israel Science Foundation and the German Israeli Projects Foundation (DIP).
We outline the fundamental processes of coherent radiation emission from a bunched charged particles beam [1]. In contrast to spontaneous emission of radiation from a random electron beam that is proportional to the number of particles N, a pre-bunched electron beam emits spontaneously coherent radiation proportional to N² through the process of (spontaneous) superradiance (SP-SR) (in the sense of Dicke’s [2]). The SP-SR emission of a bunched electron beam can be even further enhanced by a process of stimulated-superradiance (ST-SR) in the presence of a seed injected radiation field. These coherent radiation emission processes are presented in term of a radiation mode expansion model, applied to general free electron radiation schemes: Optical-Klystron, HGHG, EEHG, and coherent THz sources based on synchrotron radiation, undulator radiation or Smith-Purcell radiation. The general model of coherent spontaneous emission is also extended to the nonlinear regime - Tapering Enhanced Stimulated Superradiance (TESSA) [3], and related to the tapered wiggler section of seed-injected FELs. In X-Ray FELs these processes are convoluted with other effects, but they are guidelines for strategies of wiggler tapering efficiency enhancement.
[1] A. Gover et al., Rev. Mod. Phys. https://arxiv.org/abs/1810.07566v3 (2019)
[2] R. H. Dicke, Physical Review 93, 99 (1954)
[3] N. Sudar et al., P.R.L. 117, 174801 (2016)

Slides TUT01 [11.391 MB]

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WEA01

Overview of CW RF Guns for Short Wavelength FELs

gun, cathode, SRF, electron

290

H.J. Qian
DESY Zeuthen, Zeuthen, Germany
E. Vogel
DESY, Hamburg, Germany

Hard X-ray FELs (XFELs) operating with pulsed RF provide unprecedented peak brilliance for scientific research. Operating the accelerators with CW RF improves the flexibility w.r.t. the available time structure for experiments and opens the next frontier of average brilliance. One of the challenges of CW XFELs is the electron source, which requires both CW operation and highest possible beam quality allowing lasing at shortest wavelengths. The CW mode technically constraints the gun acceleration gradient, which is one of the keys to electron source brightness, so R&D is devoted to CW gun improvements since decades. In this contribution, the worldwide development status of CW RF guns, both normal conducting and superconducting, is reviewed.

Slides WEA01 [16.329 MB]

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paper received ※ 25 August 2019 paper accepted ※ 07 November 2019 issue date ※ 05 November 2019

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WEA04

Growing and Characterization of Cs2Te Photocatodes with Different Thicknesses at INFN LASA

cathode, electron, gun, diagnostics

297

L. Monaco, P. Michelato, D. Sertore
INFN/LASA, Segrate (MI), Italy
G. Guerini Rocco, C. Pagani
Università degli Studi di Milano & INFN, Segrate, Italy

The INFN LASA group has a long standing experience in the production of cesium telluride photocathodes for high brightness photoinjectors. The well-established recipe relies on the deposition of a typical amount of 10 nm of Te, followed by the Cs deposition until reaching the maximum QE. Nevertheless, for improving the understanding of photocathode properties, we are investigating the effect of Te thickness on the growing process, evaluating photocathode optical properties and quantum efficiency during the growing process and on the final film. These photocathodes will be then operated and analyzed in the real environment of the RF Gun at the PITZ facility in DESY Zeuthen, to estimate their impact on the electron beam properties.

Slides WEA04 [15.703 MB]

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WEB01

Identification and Mitigation of Smoke-Ring Effects in Scintillator-Based Electron Beam Images at the European XFEL

electron, diagnostics, experiment, ECR

301

G. Kube, S. Liu, A.I. Novokshonov, M. Scholz
DESY, Hamburg, Germany

Standard transverse beam profile measurements at the European XFEL are based on scintillating screen monitors using LYSO:Ce. While it is possible to resolve beam sizes down to a few micrometers with this scintillator, the experience during the XFEL commissioning showed that the measured emittance values were significantly larger than the expected ones. In addition, beam profiles measured at bunch charges of a few hundred pC showed a ’smoke ring’ structure. While coherent OTR emission and beam dynamical influence can be excluded, it is assumed that the profile distortions are caused by effects from the scintillator material. Following the experience in high energy physics, a simple model was developed which takes into account quenching effects of excitonic carriers inside a scintillator in a heuristic way. Based on this model, the observed beam profiles can be understood qualitatively. Together with the model description, first comparisons with experimental results will be shown. Possible new scintillator materials suitable for beam profile diagnostics and first test results from beam measurements will be presented.

Slides WEB01 [5.057 MB]

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WEB02

Wire-Scanners with Sub-Micrometer Resolution: Developments and Measurements

experiment, electron, operation, emittance

307

G.L. Orlandi, S. Borrelli, Ch. David, E. Ferrari, V. Guzenko, B. Hermann, O. Huerzeler, R. Ischebeck, C. Lombosi, C. Ozkan Loch, E. Prat
PSI, Villigen PSI, Switzerland
N. Cefarin, S. Dal Zilio, M. Lazzarino
IOM-CNR, Trieste, Italy
M. Ferianis, G. Penco, M. Veronese
Elettra-Sincrotrone Trieste S.C.p.A., Basovizza, Italy

Monitors of the beam transverse profile with ever more demanding spatial resolution and minimal invasivity are required by the FEL community. In order to improve the spatial resolution towards the sub-micrometer limit as well as to decrease the impact on the lasing process, nano-fabricated wire-scanners have been manufactured independently at PSI and FERMI by means of a lithographic technique [1,2]. Experimental tests carried out at SwissFEL at a low emittance demonstrated the capability of such innovative wire-scanner solutions to resolve beam transverse profiles with a size of 400-500 nm without being affected by any resolution limit. Status and outlook of nano-fabricated wire-scanners will be presented.
[1] M. Veronese et al., NIM-A, 891, 32-36, (2018).
[2] S. Borrelli et al., Comm. Phys.-Nature, 1, 52 (2018).

Slides WEB02 [11.196 MB]

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WEB04

Few-Femtosecond Facility-Wide Synchronization of the European XFEL

laser, electron, FEM, timing

318

S. Schulz, M.K. Czwalinna, M. Felber, M. Fenner, C. Gerth, T. Kozak, T. Lamb, B. Lautenschlager, F. Ludwig, U. Mavrič, J. Müller, S. Pfeiffer, H. Schlarb, Ch. Schmidt, C. Sydlo, M. Titberidze, F. Zummack
DESY, Hamburg, Germany

The first facility-wide evaluation of the optical synchronization system at the European XFEL resulted in excellent arrival time stability of the electron bunches at the end of the 2 km long linac, being measured with two individual adjacent femtosecond-resolution bunch arrival time monitors. While each of the monitors is independently linked by a stabilized optical fiber to a master laser oscillator, with one being installed in the injector area and one in the experimental hall, these two reference lasers are tightly synchronized through another few-km long fiber link. Thus, not only the accelerator performance is being benchmarked, but equally the optical synchronization infrastructure itself. Stability on this level can only be achieved by locking the RF for cavity field control to the optical reference and requires an unprecedented synchronization of the master laser oscillator to the main RF oscillator, enabled by a novel RF/optical phase detector. Finally, with the seeders of the experiment’s optical lasers synchronized to the master laser oscillator, first experiments at two independent scientific instruments proved an X-ray/optical timing jitter of few tens of femtoseconds.

Slides WEB04 [22.142 MB]

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WEP004

Timing Stability Comparison Study of RF Synthesis Techniques

timing, laser, FEM, electron

325

E. Cano Vargas, F.X. Kärtner
Deutsches Elektronen Synchrotron (DESY) and Center for Free Electron Science (CFEL), Hamburg, Germany
A. Berlin, H.P.H. Cheng, A. Dai, J. Derksen, P. Schiepel, K. Şafak
Cycle GmbH, Hamburg, Germany

Funding: Deutsches Elektronen-Synchrotron (DESY); Cycle GmbH.
High-precision and low-noise timing transfer from a master clock to different end stations of a free-electron laser (FEL) is an essential task.[1] Timing precisions ranging from few tens of femtoseconds to sub-femtoseconds are required for seeded FELs and attosecond science centers. Mode-locked lasers referenced to RF standards are commonly used as master oscillators, due to their superior stability and timing precision, depicting timing jitter in the attosecond range.[2] In this matter, one of the biggest challenges is to transfer the timing stability of mode-locked lasers to RF sources. Here, we compare and contrast two of the most common techniques used for laser-to-RF synthesis in FEL facilities: (i) RF signal extraction from the optical pulse train using photodiodes, and (ii) VCO-to-laser synchronization. Test setups are built to measure both the absolute phase noise of the generated RF signal and the relative timing jitter with respect to the mode-locked laser. Short-term timing jitter values varying between 10 and 100 fs are achieved for different test setups, while long term timing drift ranging to some hundreds of fs due to environmental influence are observed.
[1] M. Xin, K. Shafak and F.X. Kärtner, Optica, vol. 5, no. 12, pp. 1564-1578, 2018.
[2] J. Kim, F.X. Kärtner, Opt. Lett., vol. 32, pp. 3519-3521, 2007.

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WEP006

A PolariX TDS for the FLASH2 Beamline

emittance, electron, photon, optics

328

F. Christie, J. Rönsch-Schulenburg, M. Vogt
DESY, Hamburg, Germany

Transverse Deflecting RF-Structures (TDS) are successfully used for longitudinal diagnostic purposes at many Free-Electron Lasers (FEL) (LCLS, FLASH, EU-XFEL, FERMI). Moreover, by installing a TDS downstream of the FEL undulators and placing the measurement screen in a dispersive section, the temporal photon pulse structure can be estimated, as was demonstrated at LCLS and sFLASH. Here we describe the installation of a variable polarization X-band structure (PolariX TDS [1]) downstream of the FLASH2 undulators. The installation of such a TDS enables longitudinal phase space measurements and photon pulse reconstructions, as well as slice emittance measurements in both planes using the same cavity due to the unique variable polarization of the PolariX TDS.
[1] P. Craievich et al., "Status of the PolariX-TDS Project", in Proc. IPAC’18, Vancouver, Canada (2018)

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WEP007

Usage of the MicroTCA.4 Electronics Platform for Femtosecond Synchronization Systems

laser, controls, electron, timing

332

M. Felber, E.P. Felber, M. Fenner, T. Kozak, T. Lamb, J. Müller, K.P. Przygoda, H. Schlarb, S. Schulz, C. Sydlo, M. Titberidze, F. Zummack
DESY, Hamburg, Germany

At the European XFEL and FLASH at DESY optical synchronization systems are installed providing sub-10 femtosecond electron bunch arrival time stability and laser oscillator synchronization to carry out time-resolved pump-probe experiments with high precision. The synchronization system supplies critical RF stations with short- and long-term phase-stable reference signals for precise RF field detection and control while bunch arrival times are processed in beam-based feedbacks to further time-stabilize the FEL pulses. Experimental lasers are tightly locked to the optical reference using balanced optical cross-correlation. In this paper, we describe the electronic hardware for supervision and real-time control of the optical synchronization system. It comprises various MicroTCA.4 modules including fast digitizers, FPGA processor boards, and drivers for piezos and stepper-motors. Advantages of the system are the high-level of integration, state-of-the-art performance, flexibility, and remote maintainability.

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paper received ※ 20 August 2019 paper accepted ※ 26 August 2019 issue date ※ 05 November 2019

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WEP008

Multi-Beamline Operation at the European XFEL

kicker, timing, electron, undulator

335

L. Fröhlich, A. Aghababyan, V. Balandin, B. Beutner, F. Brinker, W. Decking, N. Golubeva, O. Hensler, Y. Janik, R. Kammering, H. Kay, T. Limberg, S. Liu, D. Nölle, F. Obier, M. Omet, M. Scholz, T. Wamsat, T. Wilksen, J. Wortmann
DESY, Hamburg, Germany

The European XFEL uses a unique beam distribution scheme to direct electron bunches to its three undulator lines. The accelerator delivers up to 600 microsecond long bunch trains, out of which parts or individual bunches can be selected for photon production in any of the FELs. This contribution gives a brief overview of the kicker-septum scheme facilitating this and highlights how even complex bunch patterns can easily be configured via the timing system.

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paper received ※ 19 August 2019 paper accepted ※ 29 August 2019 issue date ※ 05 November 2019

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WEP009

Long Term Stability and Slow Feedback Performance at the European XFEL

feedback, operation, undulator, linac

339

R. Kammering
DESY, Hamburg, Germany

The European XFEL is now routinely running in user operation since more than two years. Up to 8 longitudinal and 9 transversal slow feedback loops are routinely used to keep the accelerators chosen operation conditions. First tests of comparing the machine ’free-floating’ state versus fully fixing all relevant monitoring signals have been carried out and show interesting results. Here we will review the feedback systems in terms of software architecture and conceptual layout but also in respect to feedback and FEL performance.

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WEP010

Femtosecond Laser-to-RF Synchronization and RF Reference Distribution at the European XFEL

laser, feedback, FEM, linac

343

T. Lamb, M. Felber, T. Kozak, J. Müller, H. Schlarb, S. Schulz, C. Sydlo, M. Titberidze, F. Zummack
DESY, Hamburg, Germany

At the European XFEL, optical pulses from a mode-locked laser are distributed in an optical fiber network providing femtosecond stability throughout the accelerator facility. Due to the large number of RF reference clients and because of the expected higher reliability, the 1.3 GHz RF reference signals are distributed by a conventional coaxial RF distribution system. However, the provided ultra-low phase noise 1.3 GHz RF reference signals may drift over time. To remove these drifts, an optical reference module (REFM-OPT) has been developed to detect and correct environmentally induced phase errors of the RF reference. It uses a femtosecond long-term stable laser-to-RF phase detector, based on an integrated Mach-Zehnder amplitude modulator (MZM), to measure and resynchronize the RF phase with respect to the laser pulses from the optical synchronization system with high accuracy. Currently nine REFM-OPTs are permanently operated at the European XFEL, delivering femtosecond stable RF reference signals for critical accelerating field control stations. The operation experience will be reported together with a detailed evaluation of the REFM-OPT performance.

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WEP012

THz Spectroscopy with MHz Repetition Rates for Bunch Profile Reconstructions at European XFEL

flattop, radiation, electron, undulator

350

N.M. Lockmann, C. Gerth, B. Schmidt, S. Wesch
DESY, Hamburg, Germany

The European X-ray Free-Electron Laser generates most powerful and brilliant X-ray laser pulses. Exact knowledge about the longitudinal electron bunch profile is crucial for the operation of the linear accelerator as well as for photon science experiments. The only longitudinal diagnostic downstream of the main linac is based on spectroscopy of diffraction radiation (DR). The spectral intensity of the DR in the THz and infrared regime is monitored by a four-staged grating spectrometer and allows non-invasive bunch length characterization based on form factor measurements in the range 0.7 - 60 THz. As the readout and signal shaping electronics of the spectrometer allow MHz readout rates, the longitudinal bunch profile of all bunches inside the bunch train can be characterized non-invasively and simultaneously to FEL operation. In this paper, form factor measurements along the bunch train will be described and presented as well as the resulting reconstructed current profiles.

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WEP013

Fast Kicker System for European XFEL Beam Distribution

kicker, flattop, feedback, septum

353

F. Obier, W. Decking, M. Hüning, J. Wortmann
DESY, Hamburg, Germany

A special feature of the European XFEL X-ray laser is the possibility to distribute the electron bunches of one beam pulse to different free-electron laser (FEL) beam-lines. This is achieved through a combination of kickers and a Lambertson DC septum. The integration of a beam abort dump allows a flexible selection of the bunch pattern at the FEL experiment, while the superconducting linear accelerator operates with constant beam loading. The driver linac of the FEL can deliver up to 600 µs long bunch trains with a repetition rate of 10 Hz and a maximum energy of 17.5 GeV. The FEL process poses very strict requirements on the stability of the beam position and hence on all upstream magnets. It was therefore decided to split the beam distribution system into two kicker systems, long pulse kickers with very stable amplitude (flat-top) and relatively slow pulses and fast stripline kickers with moderate stability but very fast pulses. This contribution gives a brief overview of the fast kicker system.

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WEP014

Long Pulse Kicker for European XFEL Beam Distribution

kicker, flattop, timing, septum

357

F. Obier, W. Decking, M. Hüning, J. Wortmann
DESY, Hamburg, Germany

A special feature of the European XFEL X-ray laser is the possibility to distribute the electron bunches of one beam pulse to different free-electron laser (FEL) beam-lines. This is achieved through a combination of kickers and a Lambertson DC septum. The integration of a beam abort dump allows a flexible selection of the bunch pattern at the FEL experiment, while the superconducting linear accelerator operates with constant beam loading. The driver linac of the FEL can deliver up to 600 µs long bunch trains with a repetition rate of 10 Hz and a maximum energy of 17.5 GeV. The FEL process poses very strict requirements on the stability of the beam position and hence on all upstream magnets. It was therefore decided to split the beam distribution system into two kicker systems, long pulse kickers with very stable amplitude (flat-top) and relatively slow pulses and fast stripline kickers with moderate stability but very fast pulses. This contribution gives a brief overview of the long pulse kicker system.

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WEP015

Electro-Optical Bunch Length Detection at the European XFEL

laser, electron, photon, detector

360

B. Steffen, M.K. Czwalinna, C. Gerth
DESY, Hamburg, Germany
S. Bielawski, C. Evain, E. Roussel, C. Szwaj
PhLAM/CERCLA, Villeneuve d’Ascq Cedex, France

The electro-optical bunch length detection system based on electro-optic spectral decoding has been installed and is being commissioned at the European XFEL. The system is capable of recording individual longitudinal bunch profiles with sub-picosecond resolution at a bunch repetition rate of 1.13MHz . Bunch lengths and arrival times of entire bunch trains with single-bunch resolution have been measured as well as jitter and drifts for consecutive bunch trains. In addition, we are testing a second electro-optical detection strategy, the so-called photonic time-stretching, which consists of imprinting the electric field of the bunch onto a chirped laser pulse, and then "stretching" the output pulse by optical means. As a result, we obtain is a slowed down "optical replica" of the bunch shape, which can be recorded using a photodiode and GHz-range acquisition. These tests are performed in parallel with the existing spectral decoding technique based on a spectrometer in order to allow a comparative study. In this paper, we present first results for both detection strategies from electron bunches after the second bunch compressor of the European XFEL.

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paper received ※ 24 August 2019 paper accepted ※ 28 August 2019 issue date ※ 05 November 2019

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WEP019

Concept of a Novel High-Bandwidth Arrival Time Monitor for Very Low Charges as a Part of the All-Optical Synchronization Systems at XFEL and FLASH

pick-up, laser, electron, free-electron-laser

368

A. Penirschke
THM, Friedberg, Germany
W. Ackermann
TEMF, TU Darmstadt, Darmstadt, Germany
M.K. Czwalinna, H. Schlarb
DESY, Hamburg, Germany

Funding: This work is supported by the German Federal Ministry of Education and Research (BMBF) under contract no. 05K19RO1.
Numerous advanced applications of X-ray free-electron lasers require pulse durations and time resolutions in the order of only a few femtoseconds or better. The generation of these pulses to be used in time-resolved experiments require synchronization techniques that can simultaneously lock all necessary components to a precision in the range of 1 fs only. To improve the experimental conditions at existing facilities and enable future development of seeded FELs, a new all-optical synchronization system at FLASH and XFEL was implemented, which is based on pulsed optical signals rather than electronic RF signals. In collaboration with DESY, Hamburg the all-optical synchronization system is used to ensure a timing stability on the 10 fs scale at XFEL. For a future ultra-low charge operation mode down to 1 pC at XFEL an overall synchronization of (5+1)fs r.m.s. or better is necessary. This contribution presents a new concept for a ultra-wideband pick-up structure for beampipe diameters down to 10 mm for frequencies up to 100 GHz or higher and at the same time providing sufficient output signal for the attached EOMs.

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WEP024

1.3 GHz Solid State Power Amplifier for the Buncher in CTFEL Facility

electron, experiment, cavity, bunching

371

T.H. He, C.L. Lao, P. Li, X. Luo, L.J. Shan, K. Zhou
CAEP/IAE, Mianyang, Sichuan, People’s Republic of China

The THz Free Electron Laser facility (CAEP THz FEL, CTFEL) of the China Academy of Engineering Physics uses high quality electron beams to generate high average power terahertz radiations. A 1.3 GHz RF buncher is used in front of the superconducting linear accelerator of the CTFEL facility to improve the electron beams quality. The RF buncher is driven by a solid state power amplifier (SSPA), and the SSPA is feedback controlled by a low level RF (LLRF) control system to ensure the high stability of the amplitude and phase of the bunching field in the buncher cavity. The SSPA operates at 1.3 GHz and outputs 0 to 5 kW of continuous wave power. This paper mainly introduces the principle and composition of the SSPA, and presents some experiments on the RF buncher driven by the SSPA.

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paper received ※ 15 August 2019 paper accepted ※ 27 August 2019 issue date ※ 05 November 2019

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WEP034

Characterization of FEL Spectra Using Specific Figures of Merit

background, real-time, free-electron-laser, software

388

M.A. Pop, F. Curbis
MAX IV Laboratory, Lund University, Lund, Sweden
E. Allaria
Elettra-Sincrotrone Trieste S.C.p.A., Basovizza, Italy
F. Curbis
SLF, Lund, Sweden

By analyzing the spectral content of FEL electron radiation, we can gain new information about the properties of the electron bunch and on the FEL process itself. In this work, we present a peak detection algorithm and its capabilities in characterizing the spectra of seeded FEL.
This work is done in collaboration with FERMI Elettra-Sincrotrone Trieste, Area Science Park, Trieste, Italy

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WEP035

NIR Spectrometer for Bunch-Resolved, Non-Destructive Studies of Microbunching at European XFEL

electron, laser, bunching, free-electron-laser

392

S. Fahlström, M. Hamberg
Uppsala University, Uppsala, Sweden
C. Gerth, N.M. Lockmann, B. Steffen
DESY, Hamburg, Germany

At the European X-ray Free Electron Laser high brilliance femtosecond FEL radiation pulses are generated for user experiments. For this to be achieved electron bunches must be reliably produced within very tight tolerances. In order to investigate the presence of micro-bunching, i.e. charge density variation along the electron bunch with features in the micron range, a prism-based NIR spectrometer with an InGaAs sensor, sensitive in the wavelength range 900 nm to 1700 nm was installed. The spectrometer utilizes diffraction radiation (DR) generated at electron beam energies of up to 17.5 GeV. The MHz repetition rate needed for bunch resolved measurements is made possible by the KALYPSO line detector system, providing a read-out rate of up to 2.7 MHz. We present the first findings from commissioning of the NIR spectrometer, and measurements on the impact of the laser heater system for various bunch compression settings, in terms of amplitude and bunch-to-bunch variance of the NIR spectra as well as FEL pulse energy.

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reference for this paper ※ https://doi.org/10.18429/JACoW-FEL2019-WEP035

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paper received ※ 20 August 2019 paper accepted ※ 29 August 2019 issue date ※ 05 November 2019

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WEP036

The PolariX-TDS Project: Bead-Pull Measurements and High-Power Test on the Prototype

polarization, cavity, electron, status

396

P. Craievich, M. Bopp, H.-H. Braun, A. Citterio, R. Ganter, T. Kleeb, F. Marcellini, M. Pedrozzi, E. Prat, S. Reiche
PSI, Villigen PSI, Switzerland
R.W. Aßmann, F. Christie, R.T.P. D’Arcy, U. Dorda, M. Foese, P. Gonzalez Caminal, M. Hoffmann, M. Hüning, R. Jonas, O. Krebs, S. Lederer, V. Libov, B. Marchetti, D. Marx, J. Osterhoff, M. Reukauff, H. Schlarb, S. Schreiber, G. Tews, M. Vogt, A. Wagner
DESY, Hamburg, Germany
N. Catalán Lasheras, A. Grudiev, G. McMonagle, W.L. Millar, S. Pitman, K.T. Szypula, W. Wuensch, V. del Pozo Romano
CERN, Meyrin, Switzerland
W.L. Millar
Cockcroft Institute, Warrington, Cheshire, United Kingdom

A collaboration between DESY, PSI and CERN has been established to develop and build an advanced modular X- band transverse deflection structure (TDS) system with the new feature of providing variable polarization of the deflecting force. The prototype of the novel X-band TDS, the Polarizable X-band (PolariX) TDS, was fabricated at PSI following the high-precision tuning-free production process developed for the C-band Linac of the SwissFEL project. Bead-pull RF measurements were also performed at PSI to verify, in particular, that the polarization of the dipole fields does not have any rotation along the structure. The high-power test was performed at CERN and now the TDS is at DESY and has been installed in FLASHForward, where the first streaking experience with beam will be accomplished. We summarize in this paper the status of the project, the results of the bead-pull measurements and the high power test.

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reference for this paper ※ https://doi.org/10.18429/JACoW-FEL2019-WEP036

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paper received ※ 21 August 2019 paper accepted ※ 26 August 2019 issue date ※ 05 November 2019

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WEP037

RF Jitter and Electron Beam Stability in the SwissFEL Linac

linac, klystron, feedback, booster

400

Z.G. Geng, J. Alex, V.R. Arsov, P. Craievich, C.H. Gough, R. Kalt, T. Lippuner, F. Löhl, M. Pedrozzi, E. Prat, S. Reiche
PSI, Villigen PSI, Switzerland

The X-ray FEL machine SwissFEL at the Paul Scherrer Institut in Switzerland is commissioned and transiting to user operation smoothly. FEL operation requires stringent requirements for the beam stability at the linac output, such as the electron bunch arrival time, peak current and energy. Among other things, a highly stable RF system is required to guarantee the beam stability. The SwissFEL RF system is designed based on the state-of-the-art technologies that have allowed achieving excellent RF stability. The propagation of RF amplitude and phase jitter to the electron beam are analyzed theoretically and compared with the measurements performed at SwissFEL.

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reference for this paper ※ https://doi.org/10.18429/JACoW-FEL2019-WEP037

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paper received ※ 20 August 2019 paper accepted ※ 27 August 2019 issue date ※ 05 November 2019

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WEP038

Commissioning and Stability Studies of the SwissFEL Bunch-Separation System

electron, photon, operation, kicker

404

M. Paraliev, S. Dordevic, R. Ganter, C.H. Gough, N. Hiller, R.A. Krempaská, D. Voulot
PSI, Villigen PSI, Switzerland

SwissFEL is a linear electron accelerator based, X-ray Free Electron Laser at the Paul Scherrer Institute, Switzerland. It is a user oriented facility capable of producing short, high brightness X-ray pulses covering the spectral range from 1 to 50 Å. SwissFEL is designed to run in two electron bunch mode in order to serve simultaneously two experimental beamline stations (hard and soft X-ray one) at its full repetition rate. Two closely spaced (28 ns) electron bunches are accelerated in one RF macro pulse up to 3 GeV. A high stability resonant kicker system and a Lambertson septum magnet are used to separate the bunches and to send them to their respective beamlines. With the advancement of the construction of the second beamline (Athos) the bunch-separation system was successfully commissioned. In order to confirm that the beam separation process is fully transparent a stability study of the electron beam and the free electron laser in the main beamline (Aramis) was done.

Poster WEP038 [0.945 MB]

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reference for this paper ※ https://doi.org/10.18429/JACoW-FEL2019-WEP038

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paper received ※ 19 August 2019 paper accepted ※ 25 August 2019 issue date ※ 05 November 2019

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WEP042

Observations of Short-Range Wakefield Effects in TESLA-Type Superconducting RF Cavities

HOM, cavity, wakefield, MMI

412

A.H. Lumpkin, D.R. Edstrom, J. Ruan, R.M. Thurman-Keup
Fermilab, Batavia, Illinois, USA

Funding: This manuscript has been authored by Fermi Research Alliance, LLC under Contract No. DE-AC02-07CH11359 with the U.S. Department of Energy, Office of Science, Office of High Energy Physics.
The accelerators for high power X-ray free-electron laser (FEL) facilities such as the European XFEL and planned LCLS-II X-ray FEL are employing TESLA-type SCRF cavities. Beam propagation off axis in these cavities can result in both short-range and long-range transverse wakefields which can lead to emittance dilution within the micropulses and macropulses, respectively. The Fermilab Accelerator Science and Technology (FAST) facility has a unique configuration of a photocathode RF gun beam injecting two TESLA-type single cavities (CC1 and CC2) in series prior to the cryomodule. To investigate short-range wakefield effects, we used a vertical corrector between these two cavities to steer the beam off axis at an angle into CC2. A Hamamatsu synchroscan streak camera viewing a downstream OTR screen provided an image of y-t effects within the micropulses with resolutions of ~10-micron spatial and 2-ps temporal. At 500 pC/b, 50 b, and 4 mrad off-axis steering, we observed an ~100-micron head-tail centroid shift in the streak camera image. This centroid shift is consistent with a calculated short-range wakefield effect. Additional results for kick-angle compensation will be presented.

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reference for this paper ※ https://doi.org/10.18429/JACoW-FEL2019-WEP042

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paper received ※ 20 August 2019 paper accepted ※ 28 August 2019 issue date ※ 05 November 2019

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WEP045

Status of the Klystrons for the European XFEL after Commissioning and First User Operation Phase

klystron, operation, cathode, linac

420

V. Vogel (Fogel), M. Bousonville, A. Cherepenko, S. Choroba, H.-J. Eckoldt, T. Grevsmühl, V.V. Katalev, K. Machau, P. Morozov, B. Yildirim
DESY, Hamburg, Germany

At present 26 RF stations for the European XFEL are in operation. Each of the RF stations consists of a HV modulator located on the DESY campus, up to 1600 m long 10 kV HV cables that connect the modulators and the HV pulse transformers located in the underground tunnel, the horizontal multi-beam klystron (MBK), and an air filled waveguide distribution system (WG) between the klystron and the cavities input couplers. The klystrons can produce RF power up to 10 MW, 1.5 ms RF pulse length and 10 Hz repetition rate. Two RF stations of the injector have already achieved about 30,000 hours of operation, RF stations of the XFEL bunch compressor area have operated up to 20,000 hours and the klystrons in the XFEL main linac already have about 18,000 hours of operation. To increase the lifetime of the klystrons we are using a fast protection system (KLM) that is in routine operation since 2018 in addition to the common interlock system. In this article we will give a summary of the present klystrons operation status including the number of HV and RF arcs in the klystrons and in the WG system and operation statistics for the high power RF part of machine.

Poster WEP045 [0.757 MB]

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reference for this paper ※ https://doi.org/10.18429/JACoW-FEL2019-WEP045

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paper received ※ 20 August 2019 paper accepted ※ 12 September 2019 issue date ※ 05 November 2019

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WEP046

The European XFEL Photocathode Laser

laser, cathode, electron, controls

423

L. Winkelmann, A. Choudhuri, U. Grosse-Wortmann, I. Hartl, C. Li, C. Mohr, J. Müller, F. Peters, S. Pfeiffer, S.H. Salman
DESY, Hamburg, Germany

We present the Yb:fiber, Nd:YVO4 laser used to generate electrons from the RF photocathode gun at the European XFEL. The laser provides deep UV output pulses in 600 µs bursts with variable internal repetition rate (564 kHz to 4.5 MHz). Due to its robust architecture (mode-locked and synchronized fiber oscillator, Yb:fiber amplifiers and Nd:YVO4 gain blocks), the laser has operated with >99% uptime since January 2017. Using this laser, the XFEL reported energies of 17.5 GeV in July 2018, and simultaneous multi-mJ lasing in its three SASE beamlines. The laser offers two parallel outputs (1064 nm) with single pulse energies of >100 µJ and 11 ps width (FWHM). One output is converted to deep UV with efficiencies > 25%, and the second is used as a laser heater to reduce microbunching instabilities to increase SASE efficiency. Several state-of-art laser controls were implemented, including feed-forward algorithm to flatten electron charge along the bunch, active beam stabilization with < ±10 µm jitter at the photocathode, state machines for hands-off end-user operation, and temporal pulse synchronization and drift compensation to the timing jigger of the electron bunches to less than 45 fs.

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reference for this paper ※ https://doi.org/10.18429/JACoW-FEL2019-WEP046

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paper received ※ 23 August 2019 paper accepted ※ 29 August 2019 issue date ※ 05 November 2019

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WEP047

Update on the Photocathode Lifetime at FLASH and European XFEL

cathode, laser, gun, operation

427

S. Lederer, F. Brinker, S. Schreiber
DESY, Hamburg, Germany
L. Monaco, D. Sertore
INFN/LASA, Segrate (MI), Italy

The photoinjectors of FLASH and the European XFEL at DESY (Hamburg, Germany) are operated by laser driven RF-guns. In both facilities Cs2Te photocathodes are successfully used. In this paper we give an update on the lifetime, quantum efficiency (QE) and dark current of the photocathodes used over the last years. At FLASH cathode #73.3 was operated for a record lifetime of 1413 days and was replaced December 2018 by cathode #10⁵.2. At the European XFEL cathode #680.1 is in operation since December 2015, for 1356 days up to now.

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reference for this paper ※ https://doi.org/10.18429/JACoW-FEL2019-WEP047

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paper received ※ 20 August 2019 paper accepted ※ 28 August 2019 issue date ※ 05 November 2019

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WEP049

RF Power Waveguide Distribution for the RF Gun of the European XFEL at DESY

GUI, gun, klystron, cryomodule

434

B. Yildirim, S. Choroba, V.V. Katalev, P. Morozov, Y. Nachtigal
DESY, Hamburg, Germany
E.M. Apostolov
Technical University of Sofia, Sofia, Bulgaria

The first section of the European XFEL provides the 43 m long injector. The injector consists of a 1.3 GHz RF gun, a 1.3 GHz cryomodule, a 3.9 GHz cryomodule and an extensive diagnostic section. The RF gun operates with a maximum RF peak power up to 6.5 MW, 10 Hz repetition rate and up to 650 µs pulse length. The starting point in the 1.5 cell normal conducting L-Band cavity of the RF gun is a Cs2Te photocathode, which produces electron bunches, which are injected into the superconducting accelerating section of the European XFEL. The RF power is generated by a 10 MW multi beam klystron and distributed to the RF gun through a RF power waveguide distribution system. In order to enhance the reliability of the distribution system, the peak power is minimized in every section of the system by splitting the power in different branches. The RF power reaches its maximum just in front of the RF gun after combination of all branches. An additional air pressure system decreases the break down level in the waveguides of the distribution. We present the layout of the waveguide distribution system for the XFEL RF gun at DESY and report on first operation experience.

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reference for this paper ※ https://doi.org/10.18429/JACoW-FEL2019-WEP049

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paper received ※ 19 August 2019 paper accepted ※ 27 August 2019 issue date ※ 05 November 2019

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WEP054

Beam Dynamics Optimization of a Normal-Conducting Gun Based CW Injector for the European XFEL

cavity, cathode, gun, cryomodule

452

H. Shaker, S. Lal, H.J. Qian, G. Shu, F. Stephan
DESY Zeuthen, Zeuthen, Germany

The European XFEL is operating up to 17.5 GeV electron energy with maximum 0.65% duty cycle. There is a prospect for continuous wave and long pulse mode (CW/LP) operation of the European XFEL, which enables more flexible bunch pattern time structure for experiments, higher average brightness and better stability. Due to engineering limitations, the maximum electron beam energy in the CW/LP mode is about 8.6/12.8 GeV, which puts more pressure on the injector beam quality for lasing at the shortest wavelength. This paper optimizes the beam dynamics of an injector based on a normal-conducting VHF gun.

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reference for this paper ※ https://doi.org/10.18429/JACoW-FEL2019-WEP054

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paper received ※ 20 August 2019 paper accepted ※ 26 August 2019 issue date ※ 05 November 2019

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WEP055

Multiphysics Analysis of a CW VHF Gun for European XFEL

gun, cavity, simulation, vacuum

456

G. Shu, Y. Chen, S. Lal, H.J. Qian, H. Shaker, F. Stephan
DESY Zeuthen, Zeuthen, Germany

R&D for a possible future CW mode operation of European XFEL started after the successful commissioning of the pulse mode operation. For the CW electron source upgrade, a fully superconducting CW gun is under experimental development at DESY in Hamburg, and a normal conducting (NC) CW gun is under physics design at the Photo Injector Test facility at DESY in Zeuthen (PITZ) as a backup option. Based on the experience of the LBNL on a 187 MHz gun, the DESY 217 MHz gun increased the cathode gradient and RF power to 28 MV/m and 100 kW, respectively, to further improve the beam brightness. In this paper, the multiphysics analysis investigating the RF, thermal and mechanical properties of the 217 MHz NC CW gun are presented.

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reference for this paper ※ https://doi.org/10.18429/JACoW-FEL2019-WEP055

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paper received ※ 20 August 2019 paper accepted ※ 28 August 2019 issue date ※ 05 November 2019

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WEP058

Drive Laser Temporal Shaping Techniques for Shanghai Soft X-Ray Free Electron Laser

laser, electron, cathode, flattop

466

X.T. Wang, T. Lan, M. Zhang, W.Y. Zhang
SINAP, Shanghai, People’s Republic of China
L. Feng, B. Liu
SARI-CAS, Pudong, Shanghai, People’s Republic of China
C.L. Li
Shanghai Advanced Research Institute, Pudong, Shanghai, People’s Republic of China

The design of Shanghai soft X-ray free electron laser (SXFEL) is based on laser driven photocathode, which can provide emittance <2.0 mm¿mrad with 500 pC charge. The temporal shape of drive laser has significant influence on the electron beam emittance and brightness. This paper presents the transport line of drive laser system and the temporal shaping techniques for SXFEL. This drive laser produces 8 picosecond 266nm ultraviolet pulses with repetition rate 10Hz. A transverse deflecting cavity was used for indirectly characterizing the laser pulse temporal structure. Here we present the drive laser system with its temporal shaping method, and measurement results.

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reference for this paper ※ https://doi.org/10.18429/JACoW-FEL2019-WEP058

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paper received ※ 20 August 2019 paper accepted ※ 28 August 2019 issue date ※ 05 November 2019

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WEP062

Test of Cs2Te Thickness on Cathode Performance at PITZ

cathode, emittance, gun, laser

473

P.W. Huang
TUB, Beijing, People’s Republic of China
Y. Chen, M. Groß, I.I. Isaev, P. Kitisri, C. Koschitzki, M. Krasilnikov, S. Lal, X. Li, O. Lishilin, D. Melkumyan, R. Niemczyk, A. Oppelt, H.J. Qian, H. Shaker, G. Shu, F. Stephan, G. Vashchenko, T. Weilbach
DESY Zeuthen, Zeuthen, Germany
A. Grigoryan
CANDLE, Yerevan, Armenia
S. Lederer
DESY, Hamburg, Germany
P. Michelato, L. Monaco, D. Sertore
INFN/LASA, Segrate (MI), Italy

Cesium telluride is a widely used cathode in photo injectors, and its performance is one of the keys for not only emittance but also reliable operation. Over the years lots of experiences with Cs2Te photocathodes produced with the same recipe and thickness were gained at the DESY photo injectors, but cathode performance dependence on the cathode layer thickness were not investigated. In this paper, we test fresh Cs2Te cathodes with different thickness at the Photo Injector Test Facility at DESY in Zeuthen (PITZ). The QE and thermal emittance of these cathodes inside the high gradient RF gun will be compared. Besides, the injector emittance under the operation conditions of the XFEL will also be measured with these cathodes.

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reference for this paper ※ https://doi.org/10.18429/JACoW-FEL2019-WEP062

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paper received ※ 20 August 2019 paper accepted ※ 27 August 2019 issue date ※ 05 November 2019

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WEP063

The Preliminary Study of a Pre-Bunched Terahertz Free Electron Laser by a Velocity Bunching Scheme

radiation, electron, bunching, undulator

477

R. Huang, Q.K. Jia, H.T. Li, Z. Zhao
USTC/NSRL, Hefei, Anhui, People’s Republic of China

Funding: Work supported by the National Natural Science Foundation of China Grant Number 11805200
Terahertz (THz) radiation has broad applications in biological sciences, materials imaging and radar communications and so on. High-power, frequency-adjustable THz radiation sources are desired. An electron beam, generated in a photoinjector and bunched at terahertz (THz) frequency, will excite a coherent THz radiation when entering an undulator. The radiation power mainly depends on the particle number and the bunching factor of the electron beam, which is limited by the space charge effect among the microbunches and the total rf phase width the macrobunch occupied. Previously we have designed a pre-bunched THz free electron laser (FEL) with the radiation frequency covering 0.5-5 THz. While the radiation intensity for the lower frequency (below 1~THz) is not very high because of the large energy spread and the low bunching factor. We will report a THz FEL by a velocity bunching scheme, which could realize more highly bunched beam especially in the low THz frequency region. The physical design of the electron source is described in detail.

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reference for this paper ※ https://doi.org/10.18429/JACoW-FEL2019-WEP063

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paper received ※ 19 August 2019 paper accepted ※ 28 August 2019 issue date ※ 05 November 2019

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WEP064

Performance of S-Band Photocathode RF Gun With Coaxial Coupler

gun, electron, laser, cathode

481

J.H. Hong, J.H. Han, C.-K. Min
PAL, Pohang, Kyungbuk, Republic of Korea

To improve the characteristics of electron beams, new S-band photocathode RF gun with a coaxial coupler has been developed and fabricated at the Pohang Accelerator Laboratory (PAL). This new RF gun is improved the field symmetry inside the cavity cell by applying the coaxial coupler, and the cooling performance by improving the cooling lines. The RF gun is installed in the injector test facility (ITF) for high power RF test. This paper reports the recent results on the RF conditioning process and the beam tests of the RF gun with high power RF at ITF. We present and discuss the measurement results of the basic beam parameters.

Poster WEP064 [0.784 MB]

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reference for this paper ※ https://doi.org/10.18429/JACoW-FEL2019-WEP064

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paper received ※ 24 August 2019 paper accepted ※ 26 August 2019 issue date ※ 05 November 2019

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WEP070

Influence of Radiation Exposure on the FEL Performance at FLASH

undulator, radiation, simulation, operation

488

B. Faatz, M. Tischer, P. Vagin
DESY, Hamburg, Germany

FLASH has been operated as user facility for about 14 years. In this time, the total charge accelerated and transported through the FLASH1 undulator is around 35 Coulomb. Based on detailed monitoring of the radiation loss and reference measurements on degradation of the magnetic field of the undulator, we have performed simulations to study the change in FEL performance and first comparison of the simulations with the changes we observe during operation.

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reference for this paper ※ https://doi.org/10.18429/JACoW-FEL2019-WEP070

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paper received ※ 07 August 2019 paper accepted ※ 27 August 2019 issue date ※ 05 November 2019

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WEP073

Experience With MCP-Based Photon Detector at FLASH2

radiation, undulator, electron, detector

495

S. Grunewald, E. Muller, E. Schneidmiller, K.I. Tiedtke, M.V. Yurkov
DESY, Hamburg, Germany
O.I. Brovko, A.Yu. Grebentsov, E. Syresin
JINR, Dubna, Moscow Region, Russia

In this report we describe MCP-based radiation detector at FLASH2. Micro-channel plate (MCP) detects scattered radiation from a target (mesh). Use of different targets and geometrical positioning of the MCP plates provides control of photon flux on the detector. MCP detector covers the whole wavelength range of FLASH2 (from 2.x nm to 100 nm). Dynamic range spans from sub-nJ to mJ level (from spontaneous to saturation level). Relative accuracy of single-shot radiation pulse energy measurements in the exponential gain regime is about 1%. DAQ based software is under development which allows to perform cross-correlation of the SASE FEL performance with electron beam jitters. As a result, it is possible: (i) to organize efficient feedback for cancellation of machine jitters, and (ii) to use statistical techniques for characterization of SASE FEL radiation deriving such important quantities as gain curve (gain of the radiation pulse energy and its fluctuations along the undulator), radiation pulse duration, coherence time, and degree of transverse coherence. Relevant experimental results are presented in the paper.

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reference for this paper ※ https://doi.org/10.18429/JACoW-FEL2019-WEP073

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paper received ※ 19 August 2019 paper accepted ※ 26 August 2019 issue date ※ 05 November 2019

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WEP076

A Superconducting Undulator With Variable Polarization Direction for the European FEL

undulator, polarization, radiation, photon

499

Y. Li
EuXFEL, Hamburg, Germany
R. Rossmanith
DESY, Hamburg, Germany

In the SASE3 beam line at the European XFEL a planar undulator produces linearly polarized radiation. In order to obtain a circularly polarized radiation an afterburner will be installed to produce coherent radiation with variable polarization. Recently Argonne National Lab developed a super conductive undulator (called SCAPE) for a storage ring which allows to change polarization direction and field strength without moving mechanically the undulator parts. In this paper it is investigated if a similar device could be useful for an FEL. Such device is also a possible choice for the future undulator beam lines where circular and variable polarization are required.

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reference for this paper ※ https://doi.org/10.18429/JACoW-FEL2019-WEP076

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paper received ※ 19 August 2019 paper accepted ※ 17 September 2019 issue date ※ 05 November 2019

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WEP079

Effect of Heat Load on Cryo-Cooled Monochromators at the European X-Ray Free-Electron Laser: Simulations and First Experimental Observations

experiment, simulation, electron, photon

502

I. Petrov, U. Boesenberg, M. Dommach, J. Eidam, J. Hallmann, K. Kazarian, C. Kim, W. Lu, A. Madsen, J. Möller, M. Reiser, L. Samoylova, R. Shayduk, H. Sinn, V. Sleziona, A. Zozulya
EuXFEL, Schenefeld, Germany
J.W.J. Anton, S.P. Kearney, D. Shu
ANL, Lemont, Illinois, USA
X. Dong
SINAP, Shanghai, People’s Republic of China
X. Dong
SARI-CAS, Pudong, Shanghai, People’s Republic of China

European XFEL (EuXFEL) generates high-intensity ultra-short pulses at MHz repetition rate. At hard X-ray instruments, cryo-cooled silicon monochromators are used to reduce pulse bandwidth. Here, first experimental observations during commissioning of a cryo-cooled monochromator at Materials Imaging and Dynamics (MID) instrument are presented and compared with heat flow simulations. A thermal relaxation time is estimated and compared with arrival time interval between pulses. This provides the repetition rate tolerable for stable operation of monochromator.

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reference for this paper ※ https://doi.org/10.18429/JACoW-FEL2019-WEP079

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paper received ※ 19 August 2019 paper accepted ※ 25 August 2019 issue date ※ 05 November 2019

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WEP080

ROSA: Reconstruction of Spectrogram Autocorrelation for Self-Amplified Spontaneous Emission Free-Electron Lasers

radiation, electron, laser, free-electron-laser

506

S. Serkez, G. Geloni, N. Gerasimova
EuXFEL, Schenefeld, Germany
O. Gorobtsov
Cornell University, Ithaca, New York, USA
B. Sobko
LNU, Lviv, Ukraine

X-ray Free Electron Lasers (FELs) have opened new avenues in photon science, providing coherent X-ray radiation pulses orders of magnitude brighter and shorter than previously possible. The emerging concept of "beam by design" in FEL accelerator physics aims for accurate manipulation of the electron beam to tailor spectral and temporal properties of radiation for specific experimental purposes, such as X-ray pump/X-ray probe and multiple wavelength experiments. A cost-efficient method to extract information on longitudinal Wigner distribution function of emitted FEL pulses is proposed. It requires only an ensemble of measured FEL spectra.

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reference for this paper ※ https://doi.org/10.18429/JACoW-FEL2019-WEP080

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paper received ※ 20 August 2019 paper accepted ※ 26 August 2019 issue date ※ 05 November 2019

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WEP089

Pulse Energy Measurement at the SXFEL

undulator, electron, radiation, photon

521

Z.P. Liu, H.X. Deng, C. Feng, B. Liu, D. Wang, L.Y. Yu
SINAP, Shanghai, People’s Republic of China

The test facility is going to generate 8.8 nm FEL radiation using an 840 MeV electron linac passing through the two-stage cascaded HGHG-HGHG or EEHG-HGHG (high-gain harmonic generation, echo-enabled harmonic generation) scheme. Several methods have been developed to measure the power of pulse. The responsivity of silicon photodiode having no loss in the entrance window. Silicon photodiode reach saturates at the SXFEL. In this work, we simulated the attenuator transmittance for different thicknesses. We also show the preparations of the experiment results at the SXFEL .

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reference for this paper ※ https://doi.org/10.18429/JACoW-FEL2019-WEP089

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paper received ※ 20 August 2019 paper accepted ※ 28 August 2019 issue date ※ 05 November 2019

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WEP092

Spare Undulator Production for PAL-XFEL HX1 Beamline

undulator, operation, electron, permanent-magnet

524

J.H. Han, Y.G. Jung, D.E. Kim, S.J. Lee
PAL, Pohang, Kyungbuk, Republic of Korea

In the PAL-XFEL hard X-ray beamline, 20 undulator segments with a 26 mm period and a 5 m length are installed and operated for XFEL user service. One spare undulator was manufactured in December 2018. The magnetic measurements and tuning was carried out recently. We report the measurement and tuning results.

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reference for this paper ※ https://doi.org/10.18429/JACoW-FEL2019-WEP092

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paper received ※ 20 August 2019 paper accepted ※ 25 August 2019 issue date ※ 05 November 2019

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WEP093

Radiation Damage Monitoring at PAL-XFEL

undulator, radiation, monitoring, electron

528

S.J. Lee, J.H. Han, Y.G. Jung, D.E. Kim, G. Mun
PAL, Pohang, Kyungbuk, Republic of Korea

Pohang Accelerator Laboratory X-ray Free Electron Laser (PAL-XFEL) has two undulator beamlines, one hard and one soft X-ray beamlines. These two undulator beamlines are in operation since 2017. To maintain the FEL radiation property, the B-field properties of PAL-XFEL undulators need to be kept at certain level. Under the 10 GeV beam operation condition, the accumulated radiation can affect the permanent magnet properties of the undulators. However, the radiation damage of permanent magnet can be different by the operation environment and the geometry of the undulator. Accumulated radiation sensors and a miniature undulator with a few periods are installed in the PAL-XFEL hard X-ray undulator line to monitor the undulator radiation damage. In this proceeding, the radiation monitoring activities and the recent measurement results will be introduced.

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reference for this paper ※ https://doi.org/10.18429/JACoW-FEL2019-WEP093

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paper received ※ 19 August 2019 paper accepted ※ 25 August 2019 issue date ※ 05 November 2019

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WEP094

Variable-Period Variable-Pole Number Hybrid Undulator Design for Novosibirsk THz FEL

undulator, electron, radiation, permanent-magnet

531

I.V. Davidyuk, O.A. Shevchenko, V.G. Tcheskidov, N.A. Vinokurov
BINP SB RAS, Novosibirsk, Russia

The undulator developed for the first FEL of Novosibirsk FEL facility employs variable-period structure based on the hybrid undulator scheme with poles splinted into halves. The design was adapted to deliver optimal performance, estimations were made based on results of three-dimensional field simulations. According to the modeling results, the undulator will not only widen significantly the first FEL tuning range moving the long-wavelength border of the first harmonic from 200 µm to 450 µm but also provide wider aperture and increase efficiency at shorter wavelengths.

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reference for this paper ※ https://doi.org/10.18429/JACoW-FEL2019-WEP094

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paper received ※ 18 August 2019 paper accepted ※ 29 August 2019 issue date ※ 05 November 2019

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WEP095

The Athos Soft X-Ray Beamlines at SwissFEL

undulator, operation, photon, electron

535

R. Follath, U. Flechsig, L. Patthey, U.H. Wagner
PSI, Villigen PSI, Switzerland

After the successful start of the hard X-ray FEL at SwissFEL in 2016, the soft X-ray FEL ATHOS at SwissFEL is expected to deliver the first beam by end of 2019. This contribution describes the beamlines attached to the FEL and reports on the status and plans for this soft X-ray facility. The ATHOS facility will operate three end stations. Two stations are already defined and are currently in the design and construction phase whereas the third station will be defined in the future. The first station (AMO) is dedicated to Atomic and Molecular physics as well as nonlinear spectroscopy. It is expected to get light in mid 2020. The second station (Furka) is for condensed matter physics. The beamline consists of a grating monochromator and distributes the beam downstream of the grating chamber by means of horizontal deflecting mirrors. Pink and monochromatic beam operation is foreseen at all branches. The monochromator uses variable line-spacing gratings on spherical substrates with a variable included angle and operates without an entrance slit. Its mechanics is based on the SX-700 design, but with the grating facing up and the mirror facing down. The installation of the beamline will start in August 2019.

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reference for this paper ※ https://doi.org/10.18429/JACoW-FEL2019-WEP095

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paper received ※ 19 August 2019 paper accepted ※ 29 August 2019 issue date ※ 05 November 2019

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WEP100

Conceptual Design of a Permanent Magnet Undulator for Fast Pulse-to-Pulse Polarization Switching in an FEL

undulator, polarization, electron, laser

545

T.Y. Chung, C.-S. Hwang
NSRRC, Hsinchu, Taiwan

In this paper, we propose the design of an undulator to alter polarization at a fast frequency and the energy spectrum pulse-to-pulse in free-electron lasers (FELs). A fast time varying magnetic field generated in an undulator can alter characteristic light features. An electromagnetic (EM) and permanent magnet (PM) type undulator provides typically a magnetic field switching frequency below 100 Hz. Inductance and heating issues from coils limit the performance for the EM type and favor small magnetic fields and longer periods and for the PM type, strong magnetic forces between magnet arrays create undesired relative motion. In this paper, we discuss these issues and propose an undulator made of Halbach cylinders with rotating magnet arrays to switch the magnetic fields. Concept, magnet structure and performance are discussed in this note.

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reference for this paper ※ https://doi.org/10.18429/JACoW-FEL2019-WEP100

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paper received ※ 30 July 2019 paper accepted ※ 26 August 2019 issue date ※ 05 November 2019

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WEP101

Linear Polarisation via a Delta Afterburner for the CompactLight Facility

undulator, polarization, radiation, bunching

549

H.M. Castañeda Cortés, D.J. Dunning, N. Thompson
STFC/DL/ASTeC, Daresbury, Warrington, Cheshire, United Kingdom

Funding: CompactLight is funded by the European Union’s Horizon 2020 research and innovation program under Grant Agreement No.777431.
We studied the degree of polarisation of the FEL radiation from the diverted-beam scheme [1,2] using the layout of the CompactLight facility, which is in the process of being designed. To satisfy the polarisation requirements defined by the users [3] without compromising the aim of the facility to be compact, we studied a configuration comprising a helical Super Conductive Undulator (SCU) followed by a Delta afterburner (configured to generate linearly polarised light). The trade-offs between the SCU length, afterburner length, degree of polarisation and output power are presented and discussed.
[1] E. A. Schneidmiller and M. V. Yurkov, Phys. Rev. ST Accel. Beams 16, 11702 (2013)
[2] A. Lutman et al., Nature Photonics 10, 468(2016)
[3] A. Mak et al., FREIA Report 2019/01, 2019

Poster WEP101 [1.083 MB]

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paper received ※ 16 August 2019 paper accepted ※ 25 August 2019 issue date ※ 05 November 2019

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WEP103

A Plasma Attenuator for Soft X-Rays in LCLS-II

plasma, electron, cavity, controls

553

A.S. Fisher, A.L. Benwell, Y. Feng, B.T. Jacobson
SLAC, Menlo Park, California, USA

Attenuation of X-ray FEL beams is often required to avoid damaging optics and detectors during alignment, and to study fluence-dependent effects. Soft X-rays are commonly attenuated by photoabsorption in a gas such as argon. However, absorbing a mJ pulse along a meter creates a pressure wave that drives gas away from the X-ray propagation axis, until equilibrium recovers in ~1 ms. This timescale matched the 120-Hz pulse spacing of LCLS, but at the high repetition rate (up to 1 MHz) and power (up to 200 W) of LCLS-II, the attenuation of subsequent pulses is reduced. Simulations demonstrate hysteresis and erratic attenuation from gas-density depletion. Instead, we propose to replace the gas column with an argon plasma in a TM010 RF cavity. The density profile then is largely set by the RF mode. X-ray absorption becomes a perturbation compared to the energy in the plasma. An LCLS-II solid-state RF amplifier, generating up to 4 kW at 1.3 GHz, can provide the drive, and the FPGA-based low-level RF controller can be programmed to track tuning with plasma density. Several diagnostics are planned to monitor plasma properties over a fill-pressure range of 10 to 1000 Pa.

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reference for this paper ※ https://doi.org/10.18429/JACoW-FEL2019-WEP103

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paper received ※ 16 August 2019 paper accepted ※ 28 August 2019 issue date ※ 05 November 2019

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WEP104

A High-Power, High-Repetition Rate THz Source for LCLS-II Pump-Probe Experiments

wiggler, radiation, laser, injection

556

Z. Zhang, A.S. Fisher, M.C. Hoffmann, Z. Huang, B.T. Jacobson, P.S. Kirchmann, W.S. Lee, A. Lindenberg, E.A. Nanni, R.W. Schoenlein
SLAC, Menlo Park, California, USA
S. Sasaki, J.Z. Xu
ANL, Lemont, Illinois, USA

Experiments using a THz pump and an x-ray probe at an x-ray free-electron laser (XFEL) facility like LCLS-II require frequency-tunable (3 to 20 THz), narrow bandwidth ( ∼ 10\%), carrier-envelope-phase-stable THz pulses that produce high fields (>1MV/cm) at the repetition rate of the x rays and well synchronized with them. In this paper, we study a two-bunch scheme to generate THz radiation at LCLS-II: the first bunch produces THz radiation in a permanent-magnet or electromagnet wiggler immediately following the LCLS-II undulator that produces X-rays from the second bunch. The initial time delay between the two bunches is optimized to compensate for the path difference in transport. We describe the two-bunch beam dynamics, the THz wiggler and radiation, as well as the transport system bringing the THz pulses from the wiggler to the experimental hall.

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reference for this paper ※ https://doi.org/10.18429/JACoW-FEL2019-WEP104

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paper received ※ 23 August 2019 paper accepted ※ 17 September 2019 issue date ※ 05 November 2019

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WEP107

Polarizing Afterburner for the LCLS-II Undulator Line

undulator, radiation, electron, polarization

560

H.-D. Nuhn
SLAC, Menlo Park, California, USA

Funding: This work was supported by U.S. Department of Energy, Office of Basic Energy Sciences, under Contract DE-AC02-76SF00515.
A fixed-gap polarizing undulator (Delta) has been successfully operated in afterburner mode in the LCLS FEL beamline at the SLAC National Accelerator Laboratory (SLAC) from August 2014 to the end of operations of the LCLS facility in December 2018. The LCLS undulator line is currently being replaced by two new undulator lines (as part of the LCLS-II project) to operate in the hard and soft X-ray wavelength ranges. Polarizing afterburners are planned for the end of the soft X-ray (SXR) line. A new polarizing undulator (Delta-II) is being developed for two reasons: (1) increased maximum K value to be resonant over the entire operational range of the SXR beamline (2) variable gap for K value control. It has been shown that using row phase control to reduce the K value while operating in circular polarizing mode severely degrades the performance of a polarizing undulator in afterburner mode. The device is currently scheduled for installation 2020-2021. The paper will explain the need for the variable gap design backed up by beam based measurements done with the LCLS Delta undulator.

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paper received ※ 27 August 2019 paper accepted ※ 29 August 2019 issue date ※ 05 November 2019

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WED01

Experience with Short-Period, Small Gap Undulators at the SwissFEL Aramis Beamline

undulator, alignment, photon, electron

564

T. Schmidt, M. Aiba, A.D. Alarcon, C. Arrell, S. Bettoni, M. Calvi, A. Cassar, E. Ferrari, R. Follath, R. Ganter, N. Hiller, P.N. Juranič, C. Kittel, F. Löhl, E. Prat, S. Reiche, T. Schietinger, D. Voulot, U.H. Wagner
PSI, Villigen PSI, Switzerland
N.J. Sammut
University of Malta, Faculty of Engineering, Msida, Malta

The SwissFEL Aramis beamline provides hard X-ray FEL radiation down to 1 Angström with 5.8 GeV and short period, 15 mm, in-vacuum undulators (U15). To reach the maximum designed K-value of 1.8 the U15s have to be operated with vacuum gaps down to 3.0 mm. The thirteen-undulator modules are 4 m long and each of them is equipped with a pair of permanent magnet quadrupoles at the two ends, aligned magnetically to the undulator axis. Optical systems and dedicated photon diagnostics are used to check the alignment and improve the K-value calibration. In this talk the main steps of the undulator commissioning will be recalled and a systematic comparison between the magnetic results and the electron and photon based measurements will be reported to highlight achievements and open issues.

Slides WED01 [13.825 MB]

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paper received ※ 28 August 2019 paper accepted ※ 06 November 2019 issue date ※ 05 November 2019

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WED02

Absorbed Radiation Doses on the European XFEL Undulator Systems During Early User Experiments

undulator, operation, photon, radiation

569

F. Wolff-Fabris, J. Pflüger, H. Sinn
EuXFEL, Schenefeld, Germany
W. Decking, D. Nölle, F. Schmidt-Föhre
DESY, Hamburg, Germany
A. Hedqvist, F. Hellberg
Stockholm University, Stockholm, Sweden

The EuXFEL is a FEL user facility based on a superconducting accelerator with high duty cycle. Three gap movable SASE Undulator Systems using hybrid NdFeB permanent magnet segments are operated. Radiation damage on undulators can impact the quality of the SASE process and ultimately threaten user operation. We observed [1] in the commissioning phase doses up to 4 kGy and 3% demagnetization effect in a diagnostic undulator. Currently all SASE systems are used for user photon delivery and in this work we present characteristics of the absorbed radiation doses on undulators under stable conditions. Doses on the upstream segments are found to be originated in the event of occasional high energy electron losses. In contrast, towards the downstream end of a SASE system, individual segments show persistent absorbed doses which are proportional to the transmitted charge and are dominated by low energy radiation. This energy-dependence depiction shall result in distinct radiation damage thresholds for individual segments. Portable magnetic flux measurement systems allow in-situ tunnel assessment of undulator properties in order to estimate radiation dose limits for future user operation.
[1] F. Wolff-Fabris et al., J. of Phys. - Conf. Series 1067, 032025 (2018)

Slides WED02 [7.344 MB]

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paper received ※ 19 August 2019 paper accepted ※ 27 August 2019 issue date ※ 05 November 2019

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THA04

Ultrafast Magnetisation Dynamics at the Low-Fluence Limit Supported by External Magnetic Fields

laser, scattering, radiation, electron

574

M. Riepp, K. Bagschik, T. Golz, G. Grübel, L. Müller, A. Philippi-Kobs, W.R. Roseker, R. Rysov, N. Stojanovic, M. Walther
DESY, Hamburg, Germany
F. Capotondi, M. Kiskinova, D. Naumenko, E. Pedersoli
Elettra-Sincrotrone Trieste S.C.p.A., Basovizza, Italy
R. Frömter, H.P. Oepen
University of Hamburg, Institut für Experimentalphysik, Hamburg, Germany

We report on ultrafast magnetisation dynamics in ferro-magnetic cobalt/platinum multilayers upon pumping by near and mid to far infrared radiation, utilizing sub-100 femtosecond free-electron laser pulses. The evolution of the excited magnetic state is studied on femtosecond timescales with nanometre spatial resolution and element selectivity, employing time-resolved magnetic small-angle X-ray scattering. The obtained results contribute to the ongoing discussion to what extent either coupling of the electromagnetic field or rather quasi-instantaneous heating of the electron-system is the driving force for phenomena like ultrafast demagnetization or all-optical helicity-dependent switching.

Slides THA04 [4.980 MB]

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paper received ※ 19 August 2019 paper accepted ※ 19 September 2019 issue date ※ 05 November 2019

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THP001

Steffen Hard-Edge Model for Quadrupoles with Extended Fringe-Fields at the European XFEL

quadrupole, focusing, optics, linac

588

N. Golubeva, V. Balandin, W. Decking, L. Fröhlich, M. Scholz
DESY, Hamburg, Germany

For modeling of linear focusing properties of quadrupole magnets the conventional rectangular model is commonly used for the design and calculations of the linear beam optics for accelerators. At the European XFEL the quadrupole magnets are described using a more accurate Steffen hard-edge model. In this paper we discuss the application of the Steffen approach for the European XFEL quadrupoles and present the examination of the model with the orbit response matrix technique.

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reference for this paper ※ https://doi.org/10.18429/JACoW-FEL2019-THP001

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paper received ※ 20 August 2019 paper accepted ※ 25 August 2019 issue date ※ 05 November 2019

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THP002

Beam Based Alignment in all Undulator Beamlines at European XFEL

undulator, alignment, quadrupole, electron

592

M. Scholz, W. Decking
DESY, Hamburg, Germany
Y. Li
EuXFEL, Hamburg, Germany

The Free Electron Laser European XFEL aims at delivering X-rays from 0.25 keV up to 25 keV out of three SASE undulators. A good overlap of photon and electron beams is indispensable to obtain good lasing performance, especially for the higher photon energies. Thus the quadrupole magnets in the undulators must be aligned as good as possible on a straight line. This can only be realized with a beam based alignment procedure. In this paper we will report on the method that was performed at the European XFEL. We will also discuss our results.

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reference for this paper ※ https://doi.org/10.18429/JACoW-FEL2019-THP002

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paper received ※ 20 August 2019 paper accepted ※ 12 September 2019 issue date ※ 05 November 2019

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THP003

Arbitrary Order Perturbation Theory for a Time-Discrete Model of Micro-Bunching Driven by Longitudinal Space Charge

bunching, space-charge, simulation, electron

596

Ph. Amstutz
LBNL, Berkeley, California, USA
M. Vogt
DESY, Hamburg, Germany

A well established model for studying the micro-bunching instability driven by longitudinal space charge in ultra-relativistic bunches in FEL-like beamlines can be identified as a time-discrete Vlasov system with general drift maps and Poisson type collective kick maps. Here we present an arbitrary order perturbative approach for the general system and the complete all-orders solution for a special example. For this example we benchmark our theory against our Perron-Frobenius tree-code.

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reference for this paper ※ https://doi.org/10.18429/JACoW-FEL2019-THP003

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paper received ※ 20 August 2019 paper accepted ※ 29 August 2019 issue date ※ 05 November 2019

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THP009

Space Charge Field Beam Dynamics Simulations for the THz SASE FEL at PITZ

undulator, radiation, simulation, space-charge

606

S.A. Schmid, H. De Gersem, E. Gjonaj
TEMF, TU Darmstadt, Darmstadt, Germany
M. Dohlus
DESY, Hamburg, Germany
M. Krasilnikov
DESY Zeuthen, Zeuthen, Germany

Funding: This work is supported by the DFG in the framework of GRK 2128.
A proof-of-principle experiment on a THz SASE FEL is under consideration at the Photo Injector Test facility at DESY in Zeuthen (PITZ). One of its options assumes utilization of 4.0 nC bunches at 16.7 MeV [1]. In this operation mode, space charge interaction strongly influences the dynamics of the electron beam inside the undulator. In this contribution, we investigate the beam dynamics in the THz undulator of PITZ using a particle-particle interaction model based on a Lienard-Wiechert approach. We analyze the influence of retardation and radiation fields on the beam dynamics resulting in the microbunching effect. Furthermore, we compute the radiation field and estimate the radiation power at the exit of the undulator. The validity of the underlying numerical models is discussed.
[1] M. Krasilnikov et al., in Proc. ICAP’18, Key West, USA, paper TUPAF23, 2018

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paper received ※ 20 August 2019 paper accepted ※ 27 August 2019 issue date ※ 05 November 2019

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THP010

Simple and Robust Free Electron Laser Doubler

electron, laser, septum, undulator

609

S. Di Mitri, G. De Ninno, R. Fabris, S. Spampinati
Elettra-Sincrotrone Trieste S.C.p.A., Basovizza, Italy
G. De Ninno
University of Nova Gorica, Nova Gorica, Slovenia
N. Thompson
STFC/DL/ASTeC, Daresbury, Warrington, Cheshire, United Kingdom
N. Thompson
Cockcroft Institute, Warrington, Cheshire, United Kingdom

Funding: This work has received funding by the European Union’s Horizon 2020 research and innovation programme under Grant Agreement No. 777431.
We present the design of a Free-Electron Laser (FEL) doubler suitable for the simultaneous operation of two FEL lines. The doubler relies on the physical selection of two longitudinal portions of an electron bunch at low energy, and on their spatial separation at high energy. Since the two electron beamlets are naturally synchronized, FEL pump-FEL probe experiments are enabled when the two photon pulses are sent to the same experimental station. The proposed solution offers improved flexibility of operation w.r.t. existing two-pulse, two-color FEL schemes, and allows for independent control of the color, timing, intensity and angle of incidence of the radiation pulses at the user end station. Detailed numerical simulations demonstrate its feasibility at the FERMI FEL facility.

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reference for this paper ※ https://doi.org/10.18429/JACoW-FEL2019-THP010

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paper received ※ 29 July 2019 paper accepted ※ 12 September 2019 issue date ※ 05 November 2019

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THP011

Experimental Benchmarking of Wakefields at the FERMI FEL Linac and Undulator Line

wakefield, linac, electron, undulator

613

S. Di Mitri, L. Sturari
Elettra-Sincrotrone Trieste S.C.p.A., Basovizza, Italy
C. Venier, R. Vescovo
University of Trieste, Trieste, Italy

Collective effects such as wakefields affect the dynamics of high brightness electron beams in linear accelerators (linacs), and can degrade the performance of short wavelength free-electron lasers (FELs). If a reliable model of wakefields is made available, the accelerator can be designed and configured with parameters that minimize their disrupting effect. In this work, the simulated effect of geometric (diffractive) wakefields and of coherent synchrotron radiation on the electron beam energy distribution at the FERMI FEL is benchmarked with measurements, so quantifying the accuracy of the model. Wakefields modelling is then extended to the undulator line, where particle tracking confirms the limited impact of the resistive wall wakefield on the lasing process. The study reveals an overall good understanding of collective effects in the facility [1].
[1] S. Di Mitri et al., Phys. Rev. Accel. and Beams, 22, 014401 (2019)

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paper received ※ 29 July 2019 paper accepted ※ 25 August 2019 issue date ※ 05 November 2019

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THP012

Compact FEL-Driven Inverse Compton Scattering Gamma-Ray Source

photon, electron, undulator, radiation

617

M. Placidi, G. Penn
LBNL, Berkeley, California, USA
S. Di Mitri
Elettra-Sincrotrone Trieste S.C.p.A., Basovizza, Italy
C. Pellegrini
UCLA, Los Angeles, California, USA
C. Pellegrini
SLAC, Menlo Park, California, USA

We explore the feasibility of a compact source of quasi-monochromatic, multi-MeV gamma-rays based on Inverse Compton Scattering (ICS) from a high intensity ultra-violet (UV) beam generated in a free-electron laser by the electron beam itself.[1] This scheme introduces a stronger relationship between the energy of the scattered photons and that of the electron beam, resulting in a device much more compact than a classic ICS for a given scattered energy. The same electron beam is used to produce gamma-rays in the 10-20 MeV range and UV radiation in the 10-15 eV range, in a ~4x22 m2 footprint system.
[1] M. Placidi et al., NIM A 855 (2017) 55-60.

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paper received ※ 19 August 2019 paper accepted ※ 25 August 2019 issue date ※ 05 November 2019

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THP013

User Operation of Sub-Picosecond THz Coherent Transition Radiation Parasitic to a VUV FEL

electron, linac, target, radiation

621

S. Di Mitri, N. Adhlakha, E. Allaria, L. Badano, G. De Ninno, P. Di Pietro, G. Gaio, L. Giannessi, G. Penco, A. Perucchi, P. Rebernik Ribič, E. Roussel, S. Spampinati, C. Spezzani, M. Trovò, M. Veronese
Elettra-Sincrotrone Trieste S.C.p.A., Basovizza, Italy
G. De Ninno
University of Nova Gorica, Nova Gorica, Slovenia
L. Giannessi
ENEA C.R. Frascati, Frascati (Roma), Italy
S. Lupi
Coherentia, Naples, Italy
S. Lupi
Sapienza University of Rome, Roma, Italy
F. Piccirilli
IOM-CNR, Trieste, Italy
E. Roussel
PhLAM/CERLA, Villeneuve d’Ascq, France
E. Roussel
PhLAM/CERCLA, Villeneuve d’Ascq Cedex, France

Coherent transition radiation is enhanced in intensity and extended in frequency spectral range by the electron beam manipulation in the beam dump beam line of the FERMI FEL, by exploiting the interplay of coherent synchrotron radiation instability and electron beam optics [1]. Experimental observations at the TeraFERMI beamline [2] confirm intensity peaks at around 1 THz and extending up to 8.5 THz, for up to 80 µJ pulse energy integrated over the full bandwidth. By virtue of its implementation in an FEL beam dump line, this work might stimulate the development of user-oriented multi-THz beamlines parasitic and self-synchronized to VUV and X-ray FELs.
[1] S. Di Mitri et al., Scientific Reports, 8, 11661 (2018).
[2] A. Perucchi et al., Synch. Rad. News 4, 30 (2017).

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reference for this paper ※ https://doi.org/10.18429/JACoW-FEL2019-THP013

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paper received ※ 29 July 2019 paper accepted ※ 27 August 2019 issue date ※ 05 November 2019

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THP015

The X-Band Linear Compression System in Dalian Coherent Light Source

electron, simulation, RF-structure, linac

625

Y. Yu, Z. Chen, G.K. Cheng, D.X. Dai, H.L. Ding, Z.G. He, L. Huang, Q.M. Li, Z.B. Li, L. Shi, J.T. Sun, K. Tao, Y.H. Tian, G.L. Wang, Z.Q. Wang, G.R. Wu, J.Y. Yang, X.M. Yang, W.Q. Zhang
DICP, Dalian, People’s Republic of China

Dalian Coherent Light Source (DCLS) is a free-electron laser (FEL) user facility working in the extreme ultraviolet (EUV) wavelength region from 50 to 150 nm. It mainly operates on the High Gain Harmonic Generation (HGHG) mode with the seed laser, although it can also run in the Self Amplified Spontaneous Emission (SASE) mode. The brightness and bandwidth of FEL radiation strongly depends on electron bunch quality, such as normalized transverse emittance, electron bunch energy, energy spread, peak current, etc. The high peak current with uniform longitudinal distribution is especially helpful for high peak power and narrow bandwidth of FEL, although it is not easy to achieve, due to the nonlinearity of sinusoidal accelerating radio frequency (RF) field and the 2nd-order momentum compaction coefficient T566 of bunch compressor. An X-band linearizer will be installed before the bunch compressor in order to correct this nonlinearity properly. In this paper, the beam dynamics design of the X-band linear compression system in DCLS is focused, and the simulation results with Elegant are presented and discussed.

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reference for this paper ※ https://doi.org/10.18429/JACoW-FEL2019-THP015

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paper received ※ 19 August 2019 paper accepted ※ 25 August 2019 issue date ※ 05 November 2019

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THP018

Transverse Deflecting Structure Dynamics for Time-Resolved Machine Studies of Shine

electron, cavity, free-electron-laser, laser

632

J.W. Yan, H.X. Deng, B. Liu, D. Wang
SINAP, Shanghai, People’s Republic of China
H.X. Deng, B. Liu, D. Wang
SARI-CAS, Pudong, Shanghai, People’s Republic of China

Funding: National Natural Science Foundation of China (11775293), the National Key Research and Development Program of China (2016YFA0401900) and Ten Thousand Talent Program.
The transverse deflecting structure (TDS) has been widely used in modern free electron laser facilities for the longitudinal phase space diagnostics of electron beams. As the first hard x-ray free electron laser in China, the SHINE is designed to deliver photons with a repetition rate up to 1 MHz. In this paper, we present the beam dynamics study of the X-band TDS behind the undulator of SHINE. In order to prevent the screen from being damaged by electron bunches with a high repetition rate, the phase of the transverse deflecting cavity is designed to deviate from zero, and only those electron bunches that are kicked by the transverse deflecting cavity are sent to the screen. In addition, the evolutionary algorithm is introduced to optimize the lattice of the TDS line to reach the highest possible resolution.

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reference for this paper ※ https://doi.org/10.18429/JACoW-FEL2019-THP018

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paper received ※ 19 August 2019 paper accepted ※ 28 August 2019 issue date ※ 05 November 2019

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THP030

An Updated Design of the NSRRC Seeded VUV Free Electron Laser Test Facility

undulator, laser, linac, radiation

651

W.K. Lau, C.K. Chan, C.-H. Chang, C.-C. Chang, L.-H. Chang, C.H. Chen, M.C. Chou, P.J. Chou, F.Z. Hsiao, K.T. Hsu, H.P. Hsueh, K.H. Hu, C.-S. Hwang, J.-Y. Hwang, J.C. Jan, C.K. Kuan, A.P. Lee, M.-C. Lin, G.-H. Luo, K.L. Tsai
NSRRC, Hsinchu, Taiwan
A. Chao, J. Wu
SLAC, Menlo Park, California, USA
S.Y. Teng
NTHU, Hsinchu, Taiwan

In this report, we present an updated design of the facility which is a 200 nm seeded, HGHG FEL driven by a 250 MeV high brightness electron linac system with dogleg bunch compressor for generation of ultrashort intense coherent radiation in the vacuum ultraviolet region. It employs a 10-periods helical undulator for enhancement of beam energy modulation and a helical undulator of 20 mm period length as the radiator (i.e. THU20) to produce hundreds of megawatts radiation with wavelength as short as 66.7 nm. An optional planar undulator can be added to generate odd harmonics (e.g. 22.2 nm, 13.3 nm etc.) of the fundamental. The facility layout and expected FEL output performance is reported.

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reference for this paper ※ https://doi.org/10.18429/JACoW-FEL2019-THP030

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paper received ※ 20 August 2019 paper accepted ※ 29 August 2019 issue date ※ 05 November 2019

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THP033

XFEL Isochronous Chicanes: Feasibility Study

quadrupole, dipole, electron, undulator

658

N. Thompson
STFC/DL/ASTeC, Daresbury, Warrington, Cheshire, United Kingdom

FEL schemes such as High-Brightness SASE [1] and Mode-Locking [2] require electron beam delays inserted between undulator sections. These schemes have been shown in simulations to perform most effectively when the electron beam delays are very close to isochronous, i.e. the first order longitudinal dispersion is very small. To minimise the disruption to the FEL process in the inter-undulator gaps, these delays must also be as compact as possible. In this paper we study the maximum longitudinal space that a delay chicane could occupy in an XFEL operating at 6 GeV before the peak power drops below a defined threshold, and we present a limit for the maximum longitudinal dispersion of the delay chicanes. We then present the optical designs of two chicanes that satisfy the requirements of length and isochronicity and show how these designs could be realised practically using small-aperture high-field quadrupoles.
[1] PRL 110, 134802 (2013).
[2] PRL 100, 203901 (2008).

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reference for this paper ※ https://doi.org/10.18429/JACoW-FEL2019-THP033

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paper received ※ 16 August 2019 paper accepted ※ 09 September 2019 issue date ※ 05 November 2019

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THP035

Beam Shaping for High-Repetition-Rate X-Ray FELs

octupole, electron, emittance, linac

661

Y. Ding, K.L.F. Bane, Y.M. Nosochkov
SLAC, Menlo Park, California, USA

Beam shaping at normal-conducting, accelerator-based FELs, such as LCLS, plays an important role for improving lasing performance and for supporting special operating modes, such as the self-seeding scheme. Beam shaping methods include horn-collimation and dechirper manipulation. Applying the beam shaping concept to high-repetition-rate FELs driven by a superconducting linac, such as LCLS-II, beam invasive methods are not preferred due to concerns about high power deposition. We have recently studied a few shaping options for LCLS-II, such as manipulating the beam chirp before compression using corrugated devices, and modifying higher order optics terms in a chicane using octupoles. In this report we will discuss the results.

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reference for this paper ※ https://doi.org/10.18429/JACoW-FEL2019-THP035

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paper received ※ 23 August 2019 paper accepted ※ 28 August 2019 issue date ※ 05 November 2019

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THP036

Microbunch Rotation for Hard X-Ray Beam Multiplexing

quadrupole, focusing, undulator, dipole

665

R.A. Margraf, Z. Huang, J.P. MacArthur, G. Marcus
SLAC, Menlo Park, California, USA
X.J. Deng
TUB, Beijing, People’s Republic of China
Z. Huang, J.P. MacArthur, R.A. Margraf
Stanford University, Stanford, California, USA

Funding: This work was supported by the Department of Energy, Laboratory Directed Research and Development program at SLAC National Accelerator Laboratory, under contract DE-AC02-76SF00515.
Electron bunches in an undulator develop periodic density modulations, or microbunches, which enable the exponential gain of X-ray power in a SASE FEL. Many FEL applications could benefit from the ability to preserve microbunching through a dipole kick. For example, X-ray beam multiplexing can be achieved if electron bunches are kicked into separate beamlines and allowed to lase in a final undulator. The microbunches developed in upstream undulators, if properly rotated, will lase off axis, producing radiation at an angle offset from the initial beam axis. Microbunch rotation with soft X-rays was previously published and demonstrated experimentally [1], multiplexing LCLS into three X-ray beams. Additional 2018 data demonstrated multiplexing of hard X-rays. Here we describe efforts to reproduce these hard X-ray experiments using an analytical model and Genesis simulations. Our goal is to apply microbunch rotation to out-coupling from a cavity-based XFEL, (RAFEL/XFELO) [2].
[1] J. P. MacArthur et al., Physical Review X 8, 041036 (2018).
[2] G. Marcus et al. Poster TUD04 presented at FEL2019 (2019).

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reference for this paper ※ https://doi.org/10.18429/JACoW-FEL2019-THP036

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paper received ※ 24 August 2019 paper accepted ※ 26 August 2019 issue date ※ 05 November 2019

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THP041

Interaction of Powerful Electro-Magnetic Fields With Bragg Reflectors

laser, simulation, experiment, electron

673

I. Bahns, W. Hillert, P. Rauer, J. Roßbach
University of Hamburg, Institut für Experimentalphysik, Hamburg, Germany
H. Sinn
EuXFEL, Schenefeld, Germany

Funding: supported by BMBF FKZ 05K16GU4
The interaction of an X-ray free electron laser (XFEL) with a Bragg Reflector can cause a change of the lattice constant, which has a direct influence on the stability of the reflection conditions [1] and can also excite modes of vibration [2]. The dynamical thermoelastic effects of the photon-matter-interaction are simulated with a finite-element-method (FEM) using the assumptions of continuums mechanics. To compare the simulation results with measured signals, a Michelson interferometer with ultrafast photodiodes (risetime <175ps, bandwith >2GHz) has been built up. To test the experimental setup in an in-house environment a pulsed UV laser is used to introduce a temporal displacement field in a silicon crystal created by about 0.26µJ of absorbed energy. The measured signal is in agreement with the FEM simulation and has shown that if averaging over thousands of pulses is applied a resolution <0.5pm is feasible. This makes this experimental setup useful to investigate the X-ray-matter-interaction of Bragg reflectors at modern X-ray facilities.
[1] S. Stoupin et al., Physical Review B 86.5 (2012): 054301.
[2] B. Yang, S. Wang and J. Wu, J. Synchrotron Rad. (2018) 25, 166-176.

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reference for this paper ※ https://doi.org/10.18429/JACoW-FEL2019-THP041

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paper received ※ 23 August 2019 paper accepted ※ 31 October 2019 issue date ※ 05 November 2019

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THP044

The Simulation Study for Single and Multi Turn ERL Based EUV FEL

simulation, electron, linac, laser

677

K.M. Nam, G.S. Yun
POSTECH, Pohang, Kyungbuk, Republic of Korea
Y.W. Parc
PAL, Pohang, Kyungbuk, Republic of Korea

Photolithography technology is the core part of the semiconductor manufacturing process. It has required light having stronger power for higher throughput. ERL based EUV FEL is emerging as a next generation EUV source which can produce the light over 10 kW. In this study, first, EUV-FEL design, which is based on single turn, is represented. It accelerates 40 pC electron beam to 600 MeV and produces EUV, whose wavelength and power are 13.5 nm and 37 kW. Second, multiturn based design is represented. It improved compactness to make it more suitable for industrial use. As a result, the electron beam was able to obtain the kinetic energy and circulate, and the size was reduced to about half without reducing the power greatly. This study is expected to increase the practical industrialization potential of ERL-based photolithography.

Poster THP044 [0.584 MB]

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paper received ※ 20 August 2019 paper accepted ※ 28 August 2019 issue date ※ 05 November 2019

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THP047

Laser-Driven Compact Free Electron Laser Development at ELI-Beamlines

laser, electron, undulator, photon

680

A.Y. Molodozhentsev
Czech Republic Academy of Sciences, Institute of Physics, Prague, Czech Republic
J.T. Green, J. Hawke, M. Kaur, D. Kocon, G. Korn, K.O. Kruchinin
ELI-BEAMS, Prague, Czech Republic
A.R. Maier
University of Hamburg, Hamburg, Germany

Funding: Advanced research using high-intensity laser produced photons and particles (CZ.02.1.01/0.0/0.0/16₀19/0000789) from the European Regional Development Fund.
The ELI-Beamlines Centre, located near Prague (Czech Republic) is an international user facility for fundamental and applied research. Using the optical parametric chirped-pulse amplification (OPCPA) technique, the ELI-Beamlines laser system will provide the laser pulse energy up to 10 Joules with the repetition rate up to 25 Hz. Combination of new laser development with constant improvement of the LWFA electron beam parameters has great potential in future development of the compact high repetition rate Free Electron Laser. The LWFA-driven FEL project, called "LUIS", is currently under preparation at ELI-Beamlines in collaboration with the University of Hamburg. The goal of the project is the improvement of the electron beam parameters in order to demonstrate the amplification and saturation of the SASE-FEL photon power in a single unit of the FEL undulator. A successful realization of the LUIS project will open a way to a next generation of laser-driven X-FELs. An overview of the LUIS project including design features and a description of all instrumentations used to characterize the laser, plasma, electron beam, photon generation will be presented in frame of this report.

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reference for this paper ※ https://doi.org/10.18429/JACoW-FEL2019-THP047

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paper received ※ 15 August 2019 paper accepted ※ 16 September 2019 issue date ※ 05 November 2019

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THP048

Progress Towards Laser Plasma Electron Based Free Electron Laser on COXINEL

laser, electron, plasma, undulator

684

M.-E. Couprie, T. André, F. Blache, F. Bouvet, F. Briquez, Y. Dietrich, J.P. Duval, M. El Ajjouri, A. Ghaith, C. Herbeaux, N. Hubert, M. Khojoyan, C.A. Kitégi, M. Labat, N. Leclercq, A. Lestrade, A. Loulergue, O. Marcouillé, F. Marteau, D. Oumbarek Espinos, P. Rommeluère, M. Sebdaoui, K.T. Tavakoli, M. Valléau
SOLEIL, Gif-sur-Yvette, France
I.A. Andriyash, V. Malka, S. Smartzev
Weizmann Institute of Science, Physics, Rehovot, Israel
C. Benabderrahmane
ESRF, Grenoble, France
S. Bielawski, C. Evain, E. Roussel, C. Szwaj
PhLAM/CERLA, Villeneuve d’Ascq, France
S. Corde, J. Gautier, J.-P. Goddet, O.S. Kononenko, G. Lambert, K. Ta Phuoc, A. Tafzi, C. Thaury
LOA, Palaiseau, France

Laser plasma acceleration (LPA) with up to several GeV beam in very short distance appears very promising. The Free Electron Laser (FEL), though very challenging, can be viewed as a qualifying application of these new emerging LPAs. The energy spread and divergence, larger than from conventional accelerators used for FEL, have to be manipulated to fulfil the FEL requirements. On the test experiment COXINEL (ERC340015), the beam is controlled in a manipulation [1,2] line, using permanent magnet quadrupoles of variable strength [3] for emittance handing and a decompression chicane equipped with a slit for the energy selection, enabling FEL amplification for baseline reference parameters [2]. The electron position and dispersion are independently adjusted [4]. The measured spontaneous emission radiated by a 2 m long 18 mm period cryo-ready undulator exhibits the typical undulator spatio-spectral pattern, in agreement with the modelling of the electron beam travelling along the line and of the afferent photon generation. The wavelength is easily tuned with undulator gap variation. A wavelength stability of 2.6% is achieved. The undulator linewidth can be controlled.
[1] A. Loulergue et al., New J. Phys. 17 023028 (2015)
[2] M. E. Couprie et al., PPCF 58, 3 (2016)
[3] F. Marteau et al., APL 111, 253503 (2017)
[4] T. André et al., Nature Comm. 1334 (2018)

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reference for this paper ※ https://doi.org/10.18429/JACoW-FEL2019-THP048

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paper received ※ 13 August 2019 paper accepted ※ 16 September 2019 issue date ※ 05 November 2019

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THP049

A Versatile THz Source for High-Repetition Rate XFELs

GUI, radiation, undulator, electron

688

F. Lemery, M. Dohlus, K. Flöttmann, M. Marx
DESY, Hamburg, Germany
M. Ivanyan, V.M. Tsakanov
CANDLE, Yerevan, Armenia

Funding: FL was partially funded by the European Union¿s Horizon 2020 Research and Innovation programme under Grant Agreement No. 730871
The development of high-repetition rate XFELs brings an exciting time for novel fundamental science exploration via pump-probe interactions. Laser-based pump sources can provide a wide range of wavelengths (200-10000~nm) via various gain media. These sources can also be extended with optical parametric amplifiers to cover a largely versatile spectral and bandwidth range. However beyond 10~μm, toward the THz regime, there exists no suitable gain media, and optical-to-THz efficiencies are limited below 1\%. In this paper we discuss the use of Cherenkov-based radiators with conventional electron bunches to generate high-power THz radiation over a wide range of parameters for existing and future XFEL facilities.

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reference for this paper ※ https://doi.org/10.18429/JACoW-FEL2019-THP049

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paper received ※ 25 August 2019 paper accepted ※ 28 August 2019 issue date ※ 05 November 2019

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THP051

Generating Trains of Attosecond Pulses with a Free-Electron Laser

electron, laser, radiation, free-electron-laser

692

S. Serkez, G. Geloni
EuXFEL, Schenefeld, Germany
M.H. Cho, H.-S. Kang, G. Kim, J.H. Ko, C.-K. Min, I.H. Nam, C.H. Shim
PAL, Pohang, Republic of Korea
F.-J. Decker
SLAC, Menlo Park, California, USA
J.H. Ko, C.H. Shim
POSTECH, Pohang, Kyungbuk, Republic of Korea
Yu. Shvyd’ko
ANL, Lemont, Illinois, USA

Recently, a Hard X-ray Self-Seeding setup was commissioned at PAL XFEL. Its main purpose is to increase the temporal coherence of FEL radiation in an active way. We report another application of this setup to generate trains of short sub-femtosecond pulses with linked phases. We discuss preliminary results of both experiment and corresponding simulations as well as indirect diagnostics of the radiation properties.

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reference for this paper ※ https://doi.org/10.18429/JACoW-FEL2019-THP051

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paper received ※ 20 August 2019 paper accepted ※ 27 August 2019 issue date ※ 05 November 2019

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THP060

Development of RF-Undulators and Powering Sources for Compact Efficient Compton FEL-Scattrons

undulator, electron, radiation, simulation

704

A.V. Savilov, E.D. Abubakirov, N.S. Ginzburg, S.V. Kuzikov, N.Yu. Peskov, A.A. Vikharev, V.Yu. Zaslavsky
IAP/RAS, Nizhny Novgorod, Russia

Conception of Compton-type FELs operating up to X-ray band is under development currently at IAP RAS (N.Novgorod). This concept is aimed at reducing energy of a driving relativistic electron beam and thereby increasing efficiency of the electron-wave interaction in FEL, as well as achieving relative compactness of the generator. The basis of this concept is RF-undulators of a new type - the so-called ’flying’ undulators. Results of current research of these RF-undulators, their simulations and ’cold’ tests in the Ka-band are presented. For powering RF-undulators spatially-extended narrow-band Cerenkov masers are developed in the specified frequency range. In order to achieve the required sub-gigawatt power level of the pumping wave in a strongly oversized oscillator, we exploit the original idea of using two-dimensional distributed feedback implemented in the 2D doubly-periodical slow-wave structures. The design parameters of Ka-band surface-wave oscillator intended for powering RF-undulators, results of its simulation and initial experimental studies are discussed.

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reference for this paper ※ https://doi.org/10.18429/JACoW-FEL2019-THP060

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paper received ※ 15 August 2019 paper accepted ※ 25 August 2019 issue date ※ 05 November 2019

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THP061

Bayesian Optimisation for Fast and Safe Parameter Tuning of SwissFEL

target, undulator, feedback, controls

707

J. Kirschner, A. Krause, M. Mutný, M. Nonnenmacher
ETH, Zurich, Switzerland
A. Adelmann, N. Hiller, R. Ischebeck
PSI, Villigen PSI, Switzerland

Parameter tuning is a notoriously time-consuming task in accelerator facilities. As tool for global optimization with noisy evaluations, Bayesian optimization was recently shown to outperform alternative methods. By learning a model of the underlying function using all available data, the next evaluation can be chosen carefully to find the optimum with as few steps as possible and without violating any safety constraints. However, the per-step computation time increases significantly with the number of parameters and the generality of the approach can lead to slow convergence on functions that are easier to optimize. To overcome these limitations, we divide the global problem into sequential subproblems that can be solved efficiently using safe Bayesian optimization. This allows us to trade off local and global convergence and to adapt to additional structure in the objective function. Further, we provide slice-plots of the function as user feedback during the optimization. We showcase how we use our algorithm to tune up the FEL output of SwissFEL with up to 40 parameters simultaneously, and reach convergence within reasonable tuning times in the order of 30 minutes (< 2000 steps).

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paper received ※ 13 August 2019 paper accepted ※ 27 August 2019 issue date ※ 05 November 2019

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THP065

Multi-Objective FEL Design Optimisation Using Genetic Algorithms

simulation, brightness, framework, electron

711

D.J. Dunning, H.M. Castañeda Cortés, J.K. Jones, N. Thompson
STFC/DL/ASTeC, Daresbury, Warrington, Cheshire, United Kingdom
J.K. Jones, N. Thompson
Cockcroft Institute, Warrington, Cheshire, United Kingdom

Simulation studies were carried out to optimise the performance of various FEL designs, with examples including longitudinal current profile shaping for a seeded FEL, and selection of the chicane delays for the High-Brightness SASE technique. In these examples multi-objective genetic algorithms were applied to a single section of the overall facility simulation, i.e. the undulator, as is the common approach. Further studies are also reported in which a full start-to-end simulation chain was optimised, with the aim of delivering a more holistic facility design optimisation.

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paper received ※ 20 August 2019 paper accepted ※ 25 August 2019 issue date ※ 05 November 2019

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THP066

XARA: X-Band Accelerator for Research and Applications

electron, undulator, linac, photon

715

D.J. Dunning, L.S. Cowie, J.K. Jones
STFC/DL/ASTeC, Daresbury, Warrington, Cheshire, United Kingdom
L.S. Cowie, J.K. Jones
Cockcroft Institute, Warrington, Cheshire, United Kingdom
L.S. Cowie
Cockcroft Institute, Lancaster University, Lancaster, United Kingdom

XARA (X-band Accelerator for Research and Applications) is a proposal for a compact ~1 GeV/c accelerator to produce attosecond light pulses in the EUV to soft X-ray region. It is under consideration as a potential future upgrade to the CLARA facility at Daresbury Laboratory, utilising high-performance X-band RF technology to increase the electron beam momentum from 250 MeV/c. Emerging techniques for generating single-cycle undulator light [1] would give access to attosecond timescales, enabling studies of ultra-fast dynamics, while also being very compact. XARA would also enhance the existing capabilities for accelerator science R&D by incorporating X-band development and increasing the electron beam momentum for novel acceleration studies.
[1] Alan Mak et al., Rep. Prog. Phys. 82 025901 (2019)

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paper received ※ 20 August 2019 paper accepted ※ 28 August 2019 issue date ※ 05 November 2019

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THP068

LCLS-II Extruded Aluminum Undulator Vacuum Chambers — New Approaches to an Improved Aperture Surface Finish

undulator, vacuum, alignment, electron

719

G.E. Wiemerslage, P.K. Den Hartog, J. Qian, M. White
ANL, Lemont, Illinois, USA

Funding: Work at Argonne National Laboratory is supported by the U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences under contract # DE-AC02-06CH11357.
The Linac Coherent Light Source, (LCLS) the world’s first x-ray free electron laser (FEL) became operational in 2009. The Advanced Photon Source contributed to the original project by designing and building the undulator line. Two slightly different variations of these chambers were required for LCLS-II: one for a soft X-ray (SXR) undulator line, and one for a hard X-ray (HXR) undulator line. Because of the extremely short electron bunch length, a key physics requirement was to achieve the best possible surface finish within the chamber aperture. Improvements to our earlier fabrication methods allowed us to meet the critical surface roughness finish defined by RF impedance requirements. We were able to improve the surface finish from an average of 812 nm rms to 238 nm rms. The average longitudinal surface roughness slope of all chambers was to be less than 20 mrad. We achieved an average longitudinal surface roughness slope of 8.5 mrad with no chamber exceeding 20 mrad. In the end, sixty-four undulator vacuum chambers and alignment systems were delivered to SLAC for the LCLS-II Upgrade project. Here we will report on the process improvements for the fabrication of these chambers.

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paper received ※ 16 August 2019 paper accepted ※ 27 August 2019 issue date ※ 05 November 2019

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THP069

Observations on Microbunching of Electrons in Laser-Driven Plasma Accelerators and Free-Electron Lasers

laser, electron, bunching, experiment

722

A.H. Lumpkin
Fermilab, Batavia, Illinois, USA
M. Downer, M. LaBerge
The University of Texas at Austin, Austin, Texas, USA
D.W. Rule
Private Address, Silver Spring, USA

Funding: This manuscript has been authored by Fermi Research Alliance, LLC under Contract No. DE-AC02-07CH11359 with the U.S. Department of Energy, Office of Science, Office of High Energy Physics.
The periodic longitudinal density modulation of relativistic electrons at the resonant wavelength (microbunching) is a fundamental aspect of free-electron lasers (FELs). In one case, microbunching fractions reached 20% at saturation of a self-amplified spontaneous emission (SASE) FEL resulting in gains of 1 million at 530 nm [1]. In that experiment the z-dependent gain of coherent optical transition radiation (COTR) was also measured. In laser-driven plasma accelerators (LPAs), microbunching at visible wavelengths has also been recently reported as evidenced by significant COTR enhancements measured in near-field and far-field images on a single shot for the first time [2]. An analytical model for COTR interferometry (COTRI) addresses both cases. In the FEL, one identified microbunched transverse cores of 25-100 microns while in the LPA the reported transverse sizes at the exit of the LPA were a few microns. In the latter case, signal enhancements of nearly 100, 000 and extensive fringes out to 30 mrad in angle space were recorded. The broadband microbunching observed in the LPA case could act as a seed for a SASE FEL experiment with tunability in principle over the visible regime.
[1] A.H. Lumpkin et al., Phys. Rev. Lett. 88, No.23, 234801 (2002).
[2] A.H. Lumpkin, M. LaBerge, D.W. Rule et al., Proceedings of AAC18, (IEEE), (2019).

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reference for this paper ※ https://doi.org/10.18429/JACoW-FEL2019-THP069

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paper received ※ 20 August 2019 paper accepted ※ 28 August 2019 issue date ※ 05 November 2019

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THP071

Progress in High Power High Brightness Double Bunch Self-Seeding at LCLS-II

kicker, undulator, photon, electron

726

A. Halavanau, F.-J. Decker, Y. Ding, C. Emma, Z. Huang, A.K. Krasnykh, J. Krzywiński, A.A. Lutman, G. Marcus, A. Marinelli, A. Ratti, D. Zhu
SLAC, Menlo Park, California, USA
C. Pellegrini
UCLA, Los Angeles, California, USA

Funding: Work supported by the U.S. Department of Energy Contract No. DE-AC02-76SF00515.
We have previosuly shown that we can generate near TW, 15 fs duration, near transform limited X-ray pulses in the 4 to 8 keV photon energy range using the LCLS-II copper linac, two electron bunches, a 4-crystal monochromator/delay line and a fast transverse bunch kicker. The first bunch generates a strong seeding X-ray signal, and the second bunch, initially propagating off-axis, interacts with the seed in a tapered amplifier undulator, where it propagates on axis. In this paper, we investigate the design of the 4-crystal monochromator, acting also as an X-ray delay system, and of the fast kicker, in preparation of the implementation of the system in LCLS-II.

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reference for this paper ※ https://doi.org/10.18429/JACoW-FEL2019-THP071

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paper received ※ 20 August 2019 paper accepted ※ 26 August 2019 issue date ※ 05 November 2019

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THP074

FLASH: The Pioneering XUV and Soft X-Ray FEL User Facility

electron, laser, free-electron-laser, undulator

734

K. Honkavaara, S. Schreiber
DESY, Hamburg, Germany

FLASH, the free-electron laser (FEL) at DESY (Hamburg) started user operation in summer 2005. It delivers high peak and average brilliance XUV and soft X-ray FEL radiation to photon experiments. Nowadays, FLASH has a 1.25 GeV superconducting linac, and two undulator beamlines, which are operated simultaneously. This paper provides an overview of its evolution from a test facility for superconducting accelerator technology to a full-scale FEL user facility.

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reference for this paper ※ https://doi.org/10.18429/JACoW-FEL2019-THP074

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paper received ※ 20 August 2019 paper accepted ※ 27 August 2019 issue date ※ 05 November 2019

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THP078

Status of the CompactLight Design Study

linac, electron, undulator, gun

738

G. D’Auria, S. Di Mitri, R.A. Rochow
Elettra-Sincrotrone Trieste S.C.p.A., Basovizza, Italy
M. Aicheler
HIP, University of Helsinki, Finland
A. Aksoy
Ankara University Institute of Accelerator Technologies, Golbasi, Turkey
D. Alesini, M. Bellaveglia, B. Buonomo, F. Cardelli, M. Croia, M. Diomede, M. Ferrario, A. Gallo, A. Giribono, L. Piersanti, J. Scifo, B. Spataro, C. Vaccarezza
INFN/LNF, Frascati, Italy
R. Apsimon, G. Burt, A. Castilla
Cockcroft Institute, Lancaster University, Lancaster, United Kingdom
J.M. Arnesano, F. Bosco, L. Ficcadenti, A. Mostacci, L. Palumbo
Sapienza University of Rome, Rome, Italy
A. Bernhard, J. Gethmann
KIT, Karlsruhe, Germany
M. Calvi, T. Schmidt, K. Zhang
PSI, Villigen PSI, Switzerland
H.M. Castañeda Cortés, J.A. Clarke, D.J. Dunning, N. Thompson
STFC/DL/ASTeC, Daresbury, Warrington, Cheshire, United Kingdom
A.W. Cross, L. Zhang
USTRAT/SUPA, Glasgow, United Kingdom
G. Dattoli, F. Nguyen, A. Petralia
ENEA C.R. Frascati, Frascati (Roma), Italy
R.T. Dowd, D. Zhu
AS - ANSTO, Clayton, Australia
D. Esperante Pereira, J. Fuster, D. Gonzalez-Iglesias
IFIC, Valencia, Spain
W. Fang
SINAP, Shanghai, People’s Republic of China
A. Faus-Golfe, Y. Han
LAL, Orsay, France
E.N. Gazis, N. Gazis
National Technical University of Athens, Athens, Greece
R. Geometrante, M. Kokole
KYMA, Trieste, Italy
B. Gimeno
UVEG, Burjasot (Valencia), Spain
V.A. Goryashko, M. Jacewicz, R.J.M.Y. Ruber
Uppsala University, Uppsala, Sweden
R. Hoekstra
ARCNL, Amsterdam, The Netherlands
X.J.A. Janssen, J.M.A. Priem
VDL ETG, Eindhoven, The Netherlands
A. Latina, X. Liu, C. Rossi, D. Schulte, S. Stapnes, X.W. Wu, W. Wuensch
CERN, Geneva, Switzerland
O.J. Luiten, P.H.A. Mutsaers, X.F.D. Stragier
TUE, Eindhoven, The Netherlands
J. Marcos, E. Marín, R. Muñoz Horta, F. Pérez
ALBA-CELLS Synchrotron, Cerdanyola del Vallès, Spain
Z. Nergiz
Ankara University, Faculty of Sciences, Ankara, Turkey
L.J.R. Nix
University of Strathclyde, Glasgow, United Kingdom
E. Tanke, E. Trachnas
ESS, Lund, Sweden
G. Taylor
The University of Melbourne, Melbourne, Victoria, Australia

Funding: This project has received funding from the European Union’s Horizon 2020 Research and Innovation Programme under Grant Agreement No. 777431.
CompactLight (XLS) is an International Collaboration of 24 partners and 5 third parties, funded by the European Union through the Horizon 2020 Research and Innovation Programme. The main goal of the project, which started in January 2018 with a duration of 36 months, is the design of an hard X-ray FEL facility beyond today’s state of the art, using the latest concepts for bright electron photo-injectors, high-gradient accelerating structures, and innovative short-period undulators. The specifications of the facility and the parameters of the future FEL are driven by the demands of potential users and the associated science cases. In this paper we will give an overview on the ongoing activities and the major results achieved until now.

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reference for this paper ※ https://doi.org/10.18429/JACoW-FEL2019-THP078

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paper received ※ 19 August 2019 paper accepted ※ 29 August 2019 issue date ※ 05 November 2019

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THP079

Status and Perspectives of the FERMI FEL Facility (2019)

laser, electron, linac, free-electron-laser

742

L. Giannessi, E. Allaria, L. Badano, S. Bassanese, F. Bencivenga, C. Callegari, F. Capotondi, D. Castronovo, F. Cilento, P. Cinquegrana, M. Coreno, I. Cudin, G. D’Auria, M.B. Danailov, R. De Monte, G. De Ninno, P. Delgiusto, A.A. Demidovich, M. Di Fraia, S. Di Mitri, B. Diviacco, A. Fabris, R. Fabris, W.M. Fawley, M. Ferianis, L. Foglia, P. Furlan Radivo, G. Gaio, F. Gelmetti, F. Iazzourene, S. Krecic, G. Kurdi, M. Lonza, N. Mahne, M. Malvestuto, M. Manfredda, C. Masciovecchio, M. Milloch, R. Mincigrucci, N.S. Mirian, I. Nikolov, F.H. O’Shea, G. Penco, A. Perucchi, O. Plekan, M. Predonzani, K.C. Prince, E. Principi, L. Raimondi, P. Rebernik Ribič, F. Rossi, L. Rumiz, C. Scafuri, C. Serpico, N. Shafqat, P. Sigalotti, A. Simoncig, S. Spampinati, C. Spezzani, M. Svandrlik, M. Trovò, A. Vascotto, M. Veronese, R. Visintini, D. Zangrando, M. Zangrando
Elettra-Sincrotrone Trieste S.C.p.A., Basovizza, Italy

FERMI is the seeded Free Electron Laser (FEL) user facility at the Elettra laboratory in Trieste, operating in the VUV to EUV and soft X-rays spectral range; the radiation produced by the seeded FEL is characterized by wavelength stability, low temporal jitter and longitudinal coherence in the range 100-4 nm. During 2018 a dedicated experiment has shown the potential of the Echo Enabled Harmonic Generation (EEHG) scheme [1] to cover most of this spectral range with a single stage cascade [2]. Such a scheme, combined to an increment of the beam energy and of the accelerator performances, could extend the FERMI operating range toward the oxygen k-edge. With this perspective, we present the development plans under consideration for the next 3 to 5 years. These include an upgrade of the linac and of the existing FEL lines, consisting in the conversion of FEL-1 first, and FEL-2 successively, into EEHG seeded FELs.
[1] G. Stupakov, Phys. Rev. Lett. 102, 74801 (2009)
[2] P. Rebernik et al., Nature Photonics https://doi.org/10.1038/s41566-019-0427-1

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reference for this paper ※ https://doi.org/10.18429/JACoW-FEL2019-THP079

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paper received ※ 28 August 2019 paper accepted ※ 29 August 2019 issue date ※ 05 November 2019

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THP081

PolFEL — New Facility in Poland

electron, radiation, photon, experiment

746

K. Szamota-Leandersson, P.J. Czuma, P. Krawczyk, J. Krzywiński, R. Nietubyć, M. Staszczak, J. Szewiński
NCBJ, Świerk/Otwock, Poland
W. Bal, J. Poznański
IBB, Warsaw, Poland
A. Bartnik, H. Fiedorowicz, K. Janulewicz, N. Palka
MUT, Warsaw, Poland
J.K. Sekutowicz
DESY, Hamburg, Germany

Funding: European Regional Development Fund ¿ Smart Growth
In 2018 funds for the free electron laser PolFEL project was received. PolFEL will be driven by cw operating superconducting linac with SRF electron source. PolFEL will generate THz, IR and VIS-VUV radiation in two beamlines, respectively. In the first one, with electron beam below 80 MeV, the THz/IR radiation source will be generated in permanent magnet supper-radiant undulator, delivering THz radiation in 0.5 to 6 THz range. In the second beam line with up to 180 MeV electrons, the VIS/VUV radiation will be generated in the SASE undulator delivering coherent radiation down to 55 nm wavelength in the third harmonic, with sub-100 fs pulse duration. At the moment, four end-stations are planned. Experiments will be equipped with dedicated Pump-Probe spectrometer system as well. In the project, also, the Inverse Compton Scattering experiment is planned. In this contribution we will describe PolFEL facility in more details.

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reference for this paper ※ https://doi.org/10.18429/JACoW-FEL2019-THP081

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paper received ※ 29 August 2019 paper accepted ※ 18 September 2019 issue date ※ 05 November 2019

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THP084

Status of the Soft X-Ray Laser (SXL) Project at MAX IV Laboratory

linac, simulation, experiment, undulator

749

F. Curbis, J. Andersson, L. Isaksson, M. Kotur, F. Lindau, E. Mansten, M.A. Pop, H. Tarawneh, P.F. Tavares, S. Thorin, S. Werin
MAX IV Laboratory, Lund University, Lund, Sweden
S. Bonetti, A. Nilsson
Stockholm University, Stockholm, Sweden
V.A. Goryashko
Uppsala University, Uppsala, Sweden
P. Johnsson, W. Qin
Lund University, Lund, Sweden
M. Larsson, P.M. Salén
FYSIKUM, AlbaNova, Stockholm University, Stockholm, Sweden
J.A. Sellberg
KTH Physics, Stockholm, Sweden

Funding: The work is supported by Knut and Alice Wallenberg foundation.
A Soft X-ray Laser project (the SXL) aiming to produce FEL radiation in the range of 1 to 5 nm is currently in a conceptual design phase and a report on the design is expected to be delivered by March 2021. The FEL will be driven by the existing 3 GeV linac at MAX IV laboratory, which also serves as injector for the two storage rings. The science case has been pushed by a large group of mainly Swedish users and consists of experiments ranging from AMO physics to condensed matter, chemistry and imaging in life science. In this contribution, we will present the current conceptual design of the accelerator and the FEL operation modes together with a general overview of the beamline and experimental station. In particular design options for the FEL will be discussed in conjunction with the features of the electron beam from the MAX IV linac and the connection with the proposed experiments.

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reference for this paper ※ https://doi.org/10.18429/JACoW-FEL2019-THP084

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paper received ※ 21 August 2019 paper accepted ※ 28 August 2019 issue date ※ 05 November 2019

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THP085

Status of Athos, the Soft X-Ray FEL Line of SwissFEL

undulator, MMI, operation, laser

753

R. Ganter, G. Aeppli, A. Al Haddad, J. Alex, C. Arrell, V.R. Arsov, S. Bettoni, C. Bostedt, H.-H. Braun, M. Calvi, T. Celcer, P. Craievich, R. Follath, F. Frei, N. Gaiffi, Z.G. Geng, C.H. Gough, M. Huppert, R. Ischebeck, H. Jöhri, P.N. Juranič, B. Keil, F. Löhl, F. Marcellini, G. Marinkovic, G.L. Orlandi, C. Ozkan Loch, M. Paraliev, L. Patthey, M. Pedrozzi, C. Pradervand, E. Prat, S. Reiche, T. Schietinger, T. Schmidt, K. Schnorr, C. Svetina, A. Trisorio, C. Vicario, D. Voulot, U.H. Wagner, A.C. Zandonella
PSI, Villigen PSI, Switzerland

The Athos line will cover the photon energy range from 250 to 1900 eV and will operate in parallel to the hard X-ray line Aramis of SwissFEL. The paper will describe the current layout of the Athos FEL line starting from the fast kicker magnet followed by the dogleg transfer line, the small linac and the 16 APPLE undulators. From there the photon beam passes through the photonics front end and the beamline optics before reaching the experimental stations AMO and FURKA. The focus of this contribution will be on the two bunch operation commissioning (two bunches in the same RF macropulse), which started in 2018, and the characterization of the major components like the APPLE X undulator UE38, the CHIC chicane and the dechirper. The Athos installation inside the tunnel is alternating with Aramis FEL user operation and the first lasing is planned for winter 2019 / 2020.

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reference for this paper ※ https://doi.org/10.18429/JACoW-FEL2019-THP085

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paper received ※ 30 July 2019 paper accepted ※ 28 August 2019 issue date ※ 05 November 2019

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THP086

Operation Modes of the SwissFEL Soft X-Ray Beamline Athos

electron, undulator, laser, free-electron-laser

757

S. Reiche, E. Ferrari, E. Prat, T. Schietinger
PSI, Villigen PSI, Switzerland

SwissFEL drives the two FEL beamlines Aramis and Athos, a hard and soft X-ray FEL, respectively. The layout of Athos extends from a simple SASE FEL beamline with the addition of delaying chicanes, external seeding and beam manipulation with wakefield sources (dechirper). It reserves also the space for a possible upgrade to self-seeding. This presentation gives an overview on the detailed layout enabling the unique operation modes of the Athos facility.

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reference for this paper ※ https://doi.org/10.18429/JACoW-FEL2019-THP086

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paper received ※ 23 August 2019 paper accepted ※ 16 September 2019 issue date ※ 05 November 2019

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THD03

FEL Optimization: From Model-Free to Model-Dependent Approaches and ML Prospects

controls, photon, operation, undulator

762

S. Tomin, G. Geloni
EuXFEL, Schenefeld, Germany
M. Scholz
DESY, Hamburg, Germany

Users beam-time at modern FEL sources is an extremely valuable commodity. Moreover, maximization of FEL up-time must always be performed accounting for stringent requirements on the photon pulse characteristics. These may vary widely depending on the users requests, which poses issues to parallel operation of high-repetition rate facilities like the European XFEL. Therefore, both model-free or model-dependent optimization schemes, where the model might be given, or provided by machine-learning approaches, are of high importance for the overall efficiency of FEL facilities. In this contribution, we review our previous activities and we report on current efforts and progress in FEL optimization schemes at the European XFEL. Finally, we provide an outlook on future developments.

Slides THD03 [13.636 MB]

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paper received ※ 21 August 2019 paper accepted ※ 12 September 2019 issue date ※ 05 November 2019

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FRA01

FEL Operation at the European XFEL Facility

operation, photon, kicker, electron

766

D. Nölle
DESY, Hamburg, Germany

The European XFEL is a SASE FEL based user facility in the metropole region of Hamburg providing hard and soft X-ray photons with extremely high brilliance. The three FEL lines are operated simultaneously and are powered by a superconducting LINAC based on TESLA technology. Average power levels of up to several W have been demonstrated as well for soft and hard X-rays and can be requested by user experiments on day by day basis. The contribution will report on the results of the commissioning within the last two years as well as on the transition to user operation. Typical operation conditions for parallel operation of 3 SASE lines will be discussed. The perspective for the operation with an extended photon energy range, as well as for full power operation with up to 27000 pulses per second will be presented.

Slides FRA01 [27.196 MB]

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reference for this paper ※ https://doi.org/10.18429/JACoW-FEL2019-FRA01

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paper received ※ 20 August 2019 paper accepted ※ 27 August 2019 issue date ※ 05 November 2019

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FRA03

FLASH - Status and Upgrades

laser, electron, undulator, free-electron-laser

776

J. Rönsch-Schulenburg, K. Honkavaara, S. Schreiber, R. Treusch, M. Vogt
DESY, Hamburg, Germany

FLASH, the Free-Electron Laser at DESY in Hamburg was the first FEL user facility in the XUV and soft X-ray range. The superconducting RF technology allows to produce several thousand SASE pulses per second with a high peak and average brilliance. It developed to a user facility with a 1.25 GeV linear accelerator, two undulator beamlines running in parallel, and a third electron beamline containing the FLASHForward plasma wakefield experiment. Actual user operation and FEL research are discussed. New concepts and a redesign of the facility are developed to ensure that also in future FLASH will allow cutting-edge research. Upgrade plans are discussed in the contribution.

Slides FRA03 [10.554 MB]

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paper received ※ 20 August 2019 paper accepted ※ 28 August 2019 issue date ※ 05 November 2019

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