FEL2019 - List of Keywords (undulator)

Paper	Title	Other Keywords	Page
MOA07	Commissioning and First Lasing of the FELiChEM: A New IR and THz FEL Oscillator in China	FEL, electron, cavity, 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	FEL, cavity, 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	FEL, background, operation, electron	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	FEL, 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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TUP001	Extension of the PITZ Facility for a Proof-of-Principle Experiment on THz SASE FEL	radiation, FEL, 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, FEL, 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	FEL, radiation, dipole, experiment	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	FEL, 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	FEL, 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	electron, radiation, FEL, 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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TUP014	Crossed-Undulator Configuration for Variable Polarized THz Source	radiation, polarization, controls, focusing	69
	H. Saito, H. Hama, S. Kashiwagi, N.M. Morita, T. Muto, K. Nanbu, H. Yamada Tohoku University, Research Center for Electron Photon Science, Sendai, Japan
	Funding: This work was supported by JSPS KAKENHI Grant Number JP17H01070 and JP15K13401. We have developed crossed-undulator configuration to control the polarization of coherent THz radiation at the femto-second electron beam facility, t-ACTS [1], that has been established at Research Center for Electron Photon Science, Tohoku University. The t-ACTS linac equips a thermionic RF gun, a 3 m accelerating structure and a 50 MW klystron modulator. Ultra-short electron bunch (~80 fs) train can be supplied via velocity bunching scheme. The crossed-undulator system is consisted with two identical transverse undulators intersected by a chicane type phase shifter. Deflecting planes of two undulators are at right angles each other, and the phase shifter makes path length difference between the electrons and the radiation. Target radiation frequency is around 2 THz employing a beam energy of 22 MeV. Since electron bunch trails behind the radiation by the slippage-effect and the nonrelativistic-effect that the electron speed is a bit slower than the speed of light, the radiation from 1st undulator has to be much delayed rather than the electrons. The paper will report the characteristics of polarized radiation and designing work of the phase shifter. [1] H. Hama et al., Int. J. Opt Photonic Eng., 2:004, 2017.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-FEL2019-TUP014
About •	paper received ※ 24 August 2019 paper accepted ※ 17 September 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, FEL, 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	FEL, electron, simulation, 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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TUP023	Analytical and Numerical Comparison of Different Approaches to the Description of SASE in High Gain FELs	FEL, radiation, simulation, 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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TUP025	Current Status of Free Electron Laser @ TARLA	FEL, electron, cryomodule, cavity	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	FEL, 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	FEL, cavity, alignment, 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	FEL, electron, simulation, cavity	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	FEL, cavity, electron, radiation	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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TUP036	A Waveguide-Based High Efficiency Super-Radiant FEL Operating in the THz Regime	FEL, GUI, radiation, electron	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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TUP037	Optimization of the Transverse Gradient Undulator (TGU) for Application in a Storage Ring Based XFELO	electron, radiation, storage-ring, emittance	131
	Y.S. Li University of Chicago, Chicago, Illinois, USA K. Kim, R.R. Lindberg ANL, Lemont, Illinois, USA
	Funding: U.S. Dept. of Energy, Office of Science, Office of Basic Energy Sciences, under Contract No. DE-AC02-06CH11357 The stringent energy spread requirement of the XFELO poses a challenge for its application in storage rings. One way to overcome this is by using a transverse gradient undulator (TGU) [1]. The TGU gain formula was discussed previously [2]. In this paper, we begin by reviewing the analytical 3D gain formula derived from the gain convolution formula. Following that, we apply numerical optimization to investigate the optimal beam and field parameters for maximal TGU gain. We found that a small emittance ratio (i.e. "flat beam" configuration) has a strong positive impact on TGU gain, as well as other patterns in the optimal parameters. [1] T. I. Smith et al., J. Appl. Phys. 50 (1979) 4580 [2] R. R. Lindberg et al., in Proceedings FEL’13, New York, USA, 2013, pp. 740-748, paper THOBNO02
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-FEL2019-TUP037
About •	paper received ※ 19 August 2019 paper accepted ※ 27 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	simulation, electron, radiation, FEL	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	electron, radiation, FEL, 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, FEL, synchrotron	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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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	FEL, 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, FEL, radiation, bunching	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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TUP055	Two-Color Operation of FLASH2 Undulator	electron, laser, FEL, 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	FEL, 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	FEL, 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	FEL, radiation, photon, electron	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	FEL, 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, laser, photon, FEL	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	FEL, 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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TUP063	Physical Design and FEL Performance Study for FEL-III Beamline of SHINE	FEL, 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	FEL, electron, 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	electron, synchrotron, FEL, 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	FEL, simulation, electron, linac	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	FEL, 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, FEL	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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TUP074	FLASH Upgrade for Seeding	FEL, laser, 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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TUP079	Status of the Hard X-Ray Self-Seeding Setup at the European XFEL	FEL, 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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TUP080	Harmonic Off-Axis Seeding at the DELTA Short-Pulse Source	laser, electron, radiation, polarization	246
	A. Meyer auf der Heide, B. Büsing, S. Khan, D. Krieg, C. Mai DELTA, Dortmund, Germany
	Funding: Work supported by the BMBF (05K16PEA, 05K16PEB), MERCUR (Pr-2014-0047), DFG (INST 212/236-1 FUGG) and the state of NRW At the 1.5-GeV synchrotron light source DELTA operated by the TU Dortmund University, a short-pulse source employs the coherent harmonic generation (CHG) scheme. Here, a laser pulse interacts with a stored electron bunch forming a microbunching structure to generate ultrashort synchrotron light pulses at harmonics of the laser wavelength. As an upgrade of the short-pulse facility, the echo-enabled harmonic generation (EEHG) scheme will be implemented, which requires a second laser-electron interaction to yield much higher harmonics compared to CHG. In a study towards twofold laser seeding, the possibility of seeding at undulator harmonics with a crossing angle between laser and electron beam was investigated.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-FEL2019-TUP080
About •	paper received ※ 20 August 2019 paper accepted ※ 28 August 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	FEL, 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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TUP091	Start-to-End Simulation of the NSRRC Seeded VUV FEL	FEL, laser, electron, 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	FEL, photon, 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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TUD04	Cavity-Based Free-Electron Laser Research and Development: A Joint Argonne National Laboratory and SLAC National Laboratory Collaboration	FEL, electron, cavity, 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, FEL	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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WEP008	Multi-Beamline Operation at the European XFEL	FEL, kicker, timing, electron	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.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-FEL2019-WEP008
About •	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, FEL, operation, 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.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-FEL2019-WEP009
About •	paper received ※ 20 August 2019 paper accepted ※ 29 August 2019 issue date ※ 05 November 2019
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WEP012	THz Spectroscopy with MHz Repetition Rates for Bunch Profile Reconstructions at European XFEL	flattop, radiation, FEL, electron	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.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-FEL2019-WEP012
About •	paper received ※ 20 August 2019 paper accepted ※ 29 August 2019 issue date ※ 05 November 2019
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WEP027	A Fast and Accurate Method to Shim Undulator Using Multi-Objective GA	electron, MMI, laser, free-electron-laser	378
	L.G. Yan, L.J. Chen, D.R. Deng, P. Li CAEP/IAE, Mianyang, Sichuan, People’s Republic of China
	Funding: National Natural Science Foundation of China under grant of 11505174, 11505173 and 11605190 GA (Genetic Algorithm) is one of the most excellent methods to search the optimal solution for a problem, which has been applied to solve various problems. It is hard to estimate shim applied on raw undulator precisely. There are many methods have been developed to solve the problem. In this proceeding, we proposed a fast and accurate method to conclude the shim using multi-objective GA. A multi-objective objective function was set, and multi-objective optimization was also implemented. The evolution time is reduced by setting optimal evolution parameters. To demonstrate the method, we also finished some test on a prototype undulator U38. As a result, it can be achieved only by shimming three times that all the parameters of trajectory center deviation, peak-to-peak error and phase error satisfied the requirements.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-FEL2019-WEP027
About •	paper received ※ 20 August 2019 paper accepted ※ 27 August 2019 issue date ※ 05 November 2019
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WEP043	Multi-Energy Operation Analysis in a Superconducting Linac Based on off-Frequency Detune Method	linac, SRF, electron, acceleration	416
	Z. Zhang, C. Adolphsen, Y. Ding, T.O. Raubenheimer SLAC, Menlo Park, California, USA
	The free-electron laser facilities driven by a superconducting radio-frequency (SRF) linac provide high-repetition-rate electron beam, which makes it feasible to feed multiple undulator lines at the same time. In this paper, we study a method of controlling the beam energy of multiple electron bunches by off-frequency detuning of the SRF linac. Based on the theoretical analysis, we present the optimal solutions of the method and the strategy to allocate linac energy for each possible off-frequency detune. The initial acceleration phases before detuning of the SRF linac can be optimized to reduce the necessary SRF linac energy overhead. We adopt the LCLS-II-HE configuration as an example to discuss possible schemes for two undulator lines.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-FEL2019-WEP043
About •	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, FEL	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.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-FEL2019-WEP063
About •	paper received ※ 19 August 2019 paper accepted ※ 28 August 2019 issue date ※ 05 November 2019
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WEP067	Development and Commissioning of a Flip Coil System for Measuring Field Integrals	background, software, quadrupole, MMI	484
	J.E. Baader UNICAMP, Campinas, São Paulo, Brazil
	Funding: CAPES grant numbers 88881.134183/2016-01; DOE contract DE-AC02-76SF00515 in support of the LCLS-II project; and FAEPEX-UNICAMP grant number 519.292/94550-19. Many techniques for measuring magnetic fields are available for accelerator magnets. In general, methods based upon moving wires are suitable for characterizing field harmonics, and first and second field integrals. The flip coil moving wire technique stands out due to simplicity, speed, precision, and accuracy. We aimed to develop a reliable, fast and precise flip coil system capable of characterizing field integrals in the two transverse axes. The coil was a single turn loop made of insulated beryllium copper wire. The width of the loop was 5 mm. The approach of measuring second field integrals by changing the coil’s width at one of the ends was analyzed and included in the system. High-performance motorized stages performed angular and transverse positioning of the coil, while manual stages were used to stretch the wire, execute fine adjustments in its transverse position, and change coil’s geometry. Initial tests with the Earth’s field and also with a reference magnet of 126 Gauss-centimeter (G.cm) demonstrated that the system achieves repeatability of 0.2 G.cm for a 60-cm long coil. This work was carried out for the LCLS-II project at SLAC.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-FEL2019-WEP067
About •	paper received ※ 08 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	FEL, 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.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-FEL2019-WEP070
About •	paper received ※ 07 August 2019 paper accepted ※ 27 August 2019 issue date ※ 05 November 2019
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WEP072	Expected Radiation Properties of the Harmonic Afterburner at FLASH2	radiation, polarization, simulation, bunching	492
	M. Mehrjoo, B. Faatz, G. Paraskaki, M. Tischer, P. Vagin DESY, Hamburg, Germany
	We discuss the afterburner option to upgrade the FLASH2 undulator line, at the FLASH facility in the Hamburg area, for delivering short wavelengths down to approximately 1.5 nm with variable polarization. This relatively straightforward upgrade enables us the study of the scientific cases in L- absorption edges of rare earth metals. The proposed afterburner setting with an energy upgrade to 1.35 GeV would potentially cover many of the community’s requests for the short wavelengths radiation and circular polarization. We also study the influence of reverse tapering on the radiation output. This contribution presents a series of simulations for the afterburner scheme and some of the technical choices made for implementation.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-FEL2019-WEP072
About •	paper received ※ 19 August 2019 paper accepted ※ 28 October 2019 issue date ※ 05 November 2019
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WEP073	Experience With MCP-Based Photon Detector at FLASH2	radiation, FEL, 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.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-FEL2019-WEP073
About •	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	FEL, 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.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-FEL2019-WEP076
About •	paper received ※ 19 August 2019 paper accepted ※ 17 September 2019 issue date ※ 05 November 2019
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WEP085	Field Integral Measurements of DAVV Undulators and Future Measurement Plan	controls, electron, LabView, insertion	513
	M. Gehlot, S.M. Khan, R. Khullar, G. Mishra Devi Ahilya University, Indore, India J. Hussain Department of Applied Physics, UIT, Bhopal, India F. Trillaud UNAM, México, D.F., Mexico
	Funding: This work is supported by SERB-DST grant EMR/2014/00120 and financial support from UGC [F.15-1/2014-15/PDFWM-2014-15-GE-MAD-26801(SA-II)], Delhi and DGAPA of UNAM, fund PAPIIT TA100617 The Insertion device development and Application (IddA) laboratory of Devi Ahilya University, Indore, India has ongoing activities on undulator design and development. In this paper, we analyze the field integral properties of the two DAVV undulator. The first is the IddA U20 prototype NdFeB-cobalt steel hybrid in house designed device of 20 mm period length with twenty five periods. The uniform gap variable hybrid undulator provides magnetic flux density (in rms) from 2400 G to 500 G in the 10 mm to 20 mm gap range. The second is the NdFeB based U50II undulator of 50 mm period length with 20 number of periods. Hall probe results are described. A short description of the measurement plan of the undulator on the pulsed wire bench and stretched wire bench is described.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-FEL2019-WEP085
About •	paper received ※ 20 August 2019 paper accepted ※ 26 August 2019 issue date ※ 05 November 2019
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WEP086	Capabilities of Terahertz Super-Radiance from Electron Bunches Moving in Micro-Undulators	electron, radiation, GUI, laser	517
	N. Balal, V.L. Bratman, A. Friedman, Yu. Lurie Ariel University, Ariel, Israel V.L. Bratman IAP/RAS, Nizhny Novgorod, Russia
	Funding: This work was supported by the Israeli Ministry of Science, Technology and Space and by the Russian Foundation for Basic Research, grant No. 16-02-00794. An available frequency range of coherent radiation from ps bunches with high charge and moderate particle energy significantly enhances if one uses a micro-undulator with a high transverse field. Such an undulator can be implemented by redistributing a strong uniform magnetic field by a helical ferromagnetic or copper insertion. According to simulations and experiments with prototypes, a steel helix with a period of (8-10) mm and an inner diameter of (1.5-2) mm inserted in the 3T-field of solenoid can provide an undulator field with an amplitude of 0.6 T. Using a hybrid system with a permanently magnetized structure can increase this value up to 1.1 T. The necessary steel helices can be manufactured on the machine, assembled from steel wires, formed from powder, or 3D - printed. Simulations based on the WB3D code demonstrate that using such undulators with the length of (30-40) cm enable single-mode super-radiance from bunches with energy of 6 MeV, charge of 1 nC and duration of 2 ps moving in an over-sized waveguide in frequency range of 3-5 THz. The calculated efficiency of such process is (2-4)% that many times exceeds efficiency for short bunches of the same initial density.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-FEL2019-WEP086
About •	paper received ※ 14 August 2019 paper accepted ※ 28 August 2019 issue date ※ 05 November 2019
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WEP089	Pulse Energy Measurement at the SXFEL	FEL, 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 .
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-FEL2019-WEP089
About •	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	FEL, 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.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-FEL2019-WEP092
About •	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	radiation, FEL, 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.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-FEL2019-WEP093
About •	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	FEL, 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.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-FEL2019-WEP094
About •	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	FEL, 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.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-FEL2019-WEP095
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WEP097	Operational Model of the Athos Undulator Beamline	polarization, operation, background, MMI	538
	C. Kittel, M. Calvi, X. Liang, T. Schmidt PSI, Villigen PSI, Switzerland N.J. Sammut University of Malta, Information and Communication Technology, Msida, Malta
	Athos, the new Soft X-ray beamline of SwissFEL, operates 16 Apple X undulators and 15 compact chicanes to implement novel lasing schemes. With the data available after the end of the magnetic measurement campaign (middle 2020), a self-consistent set of equations will be used to summarise all the relevant properties of those devices to start their commissioning. The analytical approach planned will be discussed in great detail and tested with the preliminary experimental data available. Finally, the accuracy of this approach will be evaluated and critically compared to the requirements of the new FEL beamline.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-FEL2019-WEP097
About •	paper received ※ 27 August 2019 paper accepted ※ 28 August 2019 issue date ※ 05 November 2019
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WEP098	Advanced Operational Models of the Apple X Undulator	operation, polarization, site, photon	541
	X. Liang, M. Calvi, C. Kittel, T. Schmidt PSI, Villigen PSI, Switzerland N.J. Sammut University of Malta, Information and Communication Technology, Msida, Malta
	Athos is a new soft X-ray beamline at SwissFEL, where the Apple X type undulators will be equipped. These devices are flexible to produce light in different polarization modes. An adequate magnetic field model is required for the operation of undulator. The undulator deflection parameter K and its gradient are calculated starting from the Fourier series of the magnetic field. In the classical parallel and anti-parallel operational modes - respectively elliptical and linear modes, the variation of the magnetic field as well as its parameters are evaluated by computer modeling. The results are compared to the magnetic measurements of the first Apple X prototype.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-FEL2019-WEP098
About •	paper received ※ 27 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	polarization, electron, FEL, 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.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-FEL2019-WEP100
About •	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	FEL, 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]
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-FEL2019-WEP101
About •	paper received ※ 16 August 2019 paper accepted ※ 25 August 2019 issue date ※ 05 November 2019
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WEP107	Polarizing Afterburner for the LCLS-II Undulator Line	radiation, electron, polarization, FEL	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.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-FEL2019-WEP107
About •	paper received ※ 27 August 2019 paper accepted ※ 29 August 2019 issue date ※ 05 November 2019
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Paper

Title

Other Keywords

Page

MOA07

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

FEL, electron, cavity, 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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MOC01

Regenerative Amplifier FEL - from IR to X-Rays

FEL, cavity, 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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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

FEL, background, operation, electron

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

FEL, 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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TUP001

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

radiation, FEL, 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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TUP002

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

laser, FEL, 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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TUP003

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

FEL, radiation, dipole, experiment

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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TUP004

A Superradiant THz Undulator Source for XFELs

FEL, 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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TUP006

The FHI FEL Upgrade Design

FEL, 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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TUP008

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

electron, radiation, FEL, 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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TUP014

Crossed-Undulator Configuration for Variable Polarized THz Source

radiation, polarization, controls, focusing

69

H. Saito, H. Hama, S. Kashiwagi, N.M. Morita, T. Muto, K. Nanbu, H. Yamada
Tohoku University, Research Center for Electron Photon Science, Sendai, Japan

Funding: This work was supported by JSPS KAKENHI Grant Number JP17H01070 and JP15K13401.
We have developed crossed-undulator configuration to control the polarization of coherent THz radiation at the femto-second electron beam facility, t-ACTS [1], that has been established at Research Center for Electron Photon Science, Tohoku University. The t-ACTS linac equips a thermionic RF gun, a 3 m accelerating structure and a 50 MW klystron modulator. Ultra-short electron bunch (~80 fs) train can be supplied via velocity bunching scheme. The crossed-undulator system is consisted with two identical transverse undulators intersected by a chicane type phase shifter. Deflecting planes of two undulators are at right angles each other, and the phase shifter makes path length difference between the electrons and the radiation. Target radiation frequency is around 2 THz employing a beam energy of 22 MeV. Since electron bunch trails behind the radiation by the slippage-effect and the nonrelativistic-effect that the electron speed is a bit slower than the speed of light, the radiation from 1st undulator has to be much delayed rather than the electrons. The paper will report the characteristics of polarized radiation and designing work of the phase shifter.
[1] H. Hama et al., Int. J. Opt Photonic Eng., 2:004, 2017.

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TUP015

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

radiation, electron, FEL, 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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reference for this paper ※ https://doi.org/10.18429/JACoW-FEL2019-TUP015

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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

FEL, electron, simulation, 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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reference for this paper ※ https://doi.org/10.18429/JACoW-FEL2019-TUP017

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paper received ※ 20 August 2019 paper accepted ※ 25 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

FEL, radiation, simulation, 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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reference for this paper ※ https://doi.org/10.18429/JACoW-FEL2019-TUP023

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

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TUP025

Current Status of Free Electron Laser @ TARLA

FEL, electron, cryomodule, cavity

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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reference for this paper ※ https://doi.org/10.18429/JACoW-FEL2019-TUP025

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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

FEL, 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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reference for this paper ※ https://doi.org/10.18429/JACoW-FEL2019-TUP026

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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

FEL, cavity, alignment, 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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reference for this paper ※ https://doi.org/10.18429/JACoW-FEL2019-TUP027

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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

FEL, electron, simulation, cavity

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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reference for this paper ※ https://doi.org/10.18429/JACoW-FEL2019-TUP028

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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

FEL, cavity, electron, radiation

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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reference for this paper ※ https://doi.org/10.18429/JACoW-FEL2019-TUP032

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paper received ※ 24 August 2019 paper accepted ※ 26 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

FEL, GUI, radiation, electron

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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TUP037

Optimization of the Transverse Gradient Undulator (TGU) for Application in a Storage Ring Based XFELO

electron, radiation, storage-ring, emittance

131

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

Funding: U.S. Dept. of Energy, Office of Science, Office of Basic Energy Sciences, under Contract No. DE-AC02-06CH11357
The stringent energy spread requirement of the XFELO poses a challenge for its application in storage rings. One way to overcome this is by using a transverse gradient undulator (TGU) [1]. The TGU gain formula was discussed previously [2]. In this paper, we begin by reviewing the analytical 3D gain formula derived from the gain convolution formula. Following that, we apply numerical optimization to investigate the optimal beam and field parameters for maximal TGU gain. We found that a small emittance ratio (i.e. "flat beam" configuration) has a strong positive impact on TGU gain, as well as other patterns in the optimal parameters.
[1] T. I. Smith et al., J. Appl. Phys. 50 (1979) 4580
[2] R. R. Lindberg et al., in Proceedings FEL’13, New York, USA, 2013, pp. 740-748, paper THOBNO02

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paper received ※ 19 August 2019 paper accepted ※ 27 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

simulation, electron, radiation, FEL

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

electron, radiation, FEL, 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, FEL, synchrotron

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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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

FEL, 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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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, FEL, radiation, bunching

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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TUP055

Two-Color Operation of FLASH2 Undulator

electron, laser, FEL, 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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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

FEL, 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

FEL, 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

FEL, radiation, photon, electron

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

FEL, 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, laser, photon, FEL

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

FEL, 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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TUP063

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

FEL, 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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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

FEL, electron, 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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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

electron, synchrotron, FEL, 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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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

FEL, simulation, electron, linac

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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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

FEL, 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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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, FEL

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

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TUP074

FLASH Upgrade for Seeding

FEL, laser, 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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paper received ※ 19 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

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

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TUP080

Harmonic Off-Axis Seeding at the DELTA Short-Pulse Source

laser, electron, radiation, polarization

246

A. Meyer auf der Heide, B. Büsing, S. Khan, D. Krieg, C. Mai
DELTA, Dortmund, Germany

Funding: Work supported by the BMBF (05K16PEA, 05K16PEB), MERCUR (Pr-2014-0047), DFG (INST 212/236-1 FUGG) and the state of NRW
At the 1.5-GeV synchrotron light source DELTA operated by the TU Dortmund University, a short-pulse source employs the coherent harmonic generation (CHG) scheme. Here, a laser pulse interacts with a stored electron bunch forming a microbunching structure to generate ultrashort synchrotron light pulses at harmonics of the laser wavelength. As an upgrade of the short-pulse facility, the echo-enabled harmonic generation (EEHG) scheme will be implemented, which requires a second laser-electron interaction to yield much higher harmonics compared to CHG. In a study towards twofold laser seeding, the possibility of seeding at undulator harmonics with a crossing angle between laser and electron beam was investigated.

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paper received ※ 20 August 2019 paper accepted ※ 28 August 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

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

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TUP091

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

FEL, laser, electron, 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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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

FEL, photon, 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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TUD04

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

FEL, electron, cavity, 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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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, FEL

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

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WEP008

Multi-Beamline Operation at the European XFEL

FEL, kicker, timing, electron

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, FEL, operation, 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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WEP012

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

flattop, radiation, FEL, electron

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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WEP027

A Fast and Accurate Method to Shim Undulator Using Multi-Objective GA

electron, MMI, laser, free-electron-laser

378

L.G. Yan, L.J. Chen, D.R. Deng, P. Li
CAEP/IAE, Mianyang, Sichuan, People’s Republic of China

Funding: National Natural Science Foundation of China under grant of 11505174, 11505173 and 11605190
GA (Genetic Algorithm) is one of the most excellent methods to search the optimal solution for a problem, which has been applied to solve various problems. It is hard to estimate shim applied on raw undulator precisely. There are many methods have been developed to solve the problem. In this proceeding, we proposed a fast and accurate method to conclude the shim using multi-objective GA. A multi-objective objective function was set, and multi-objective optimization was also implemented. The evolution time is reduced by setting optimal evolution parameters. To demonstrate the method, we also finished some test on a prototype undulator U38. As a result, it can be achieved only by shimming three times that all the parameters of trajectory center deviation, peak-to-peak error and phase error satisfied the requirements.

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WEP043

Multi-Energy Operation Analysis in a Superconducting Linac Based on off-Frequency Detune Method

linac, SRF, electron, acceleration

416

Z. Zhang, C. Adolphsen, Y. Ding, T.O. Raubenheimer
SLAC, Menlo Park, California, USA

The free-electron laser facilities driven by a superconducting radio-frequency (SRF) linac provide high-repetition-rate electron beam, which makes it feasible to feed multiple undulator lines at the same time. In this paper, we study a method of controlling the beam energy of multiple electron bunches by off-frequency detuning of the SRF linac. Based on the theoretical analysis, we present the optimal solutions of the method and the strategy to allocate linac energy for each possible off-frequency detune. The initial acceleration phases before detuning of the SRF linac can be optimized to reduce the necessary SRF linac energy overhead. We adopt the LCLS-II-HE configuration as an example to discuss possible schemes for two undulator lines.

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WEP063

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

radiation, electron, bunching, FEL

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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WEP067

Development and Commissioning of a Flip Coil System for Measuring Field Integrals

background, software, quadrupole, MMI

484

J.E. Baader
UNICAMP, Campinas, São Paulo, Brazil

Funding: CAPES grant numbers 88881.134183/2016-01; DOE contract DE-AC02-76SF00515 in support of the LCLS-II project; and FAEPEX-UNICAMP grant number 519.292/94550-19.
Many techniques for measuring magnetic fields are available for accelerator magnets. In general, methods based upon moving wires are suitable for characterizing field harmonics, and first and second field integrals. The flip coil moving wire technique stands out due to simplicity, speed, precision, and accuracy. We aimed to develop a reliable, fast and precise flip coil system capable of characterizing field integrals in the two transverse axes. The coil was a single turn loop made of insulated beryllium copper wire. The width of the loop was 5 mm. The approach of measuring second field integrals by changing the coil’s width at one of the ends was analyzed and included in the system. High-performance motorized stages performed angular and transverse positioning of the coil, while manual stages were used to stretch the wire, execute fine adjustments in its transverse position, and change coil’s geometry. Initial tests with the Earth’s field and also with a reference magnet of 126 Gauss-centimeter (G.cm) demonstrated that the system achieves repeatability of 0.2 G.cm for a 60-cm long coil. This work was carried out for the LCLS-II project at SLAC.

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reference for this paper ※ https://doi.org/10.18429/JACoW-FEL2019-WEP067

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paper received ※ 08 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

FEL, 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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WEP072

Expected Radiation Properties of the Harmonic Afterburner at FLASH2

radiation, polarization, simulation, bunching

492

M. Mehrjoo, B. Faatz, G. Paraskaki, M. Tischer, P. Vagin
DESY, Hamburg, Germany

We discuss the afterburner option to upgrade the FLASH2 undulator line, at the FLASH facility in the Hamburg area, for delivering short wavelengths down to approximately 1.5 nm with variable polarization. This relatively straightforward upgrade enables us the study of the scientific cases in L- absorption edges of rare earth metals. The proposed afterburner setting with an energy upgrade to 1.35 GeV would potentially cover many of the community’s requests for the short wavelengths radiation and circular polarization. We also study the influence of reverse tapering on the radiation output. This contribution presents a series of simulations for the afterburner scheme and some of the technical choices made for implementation.

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reference for this paper ※ https://doi.org/10.18429/JACoW-FEL2019-WEP072

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

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WEP073

Experience With MCP-Based Photon Detector at FLASH2

radiation, FEL, 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

FEL, 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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WEP085

Field Integral Measurements of DAVV Undulators and Future Measurement Plan

controls, electron, LabView, insertion

513

M. Gehlot, S.M. Khan, R. Khullar, G. Mishra
Devi Ahilya University, Indore, India
J. Hussain
Department of Applied Physics, UIT, Bhopal, India
F. Trillaud
UNAM, México, D.F., Mexico

Funding: This work is supported by SERB-DST grant EMR/2014/00120 and financial support from UGC [F.15-1/2014-15/PDFWM-2014-15-GE-MAD-26801(SA-II)], Delhi and DGAPA of UNAM, fund PAPIIT TA100617
The Insertion device development and Application (IddA) laboratory of Devi Ahilya University, Indore, India has ongoing activities on undulator design and development. In this paper, we analyze the field integral properties of the two DAVV undulator. The first is the IddA U20 prototype NdFeB-cobalt steel hybrid in house designed device of 20 mm period length with twenty five periods. The uniform gap variable hybrid undulator provides magnetic flux density (in rms) from 2400 G to 500 G in the 10 mm to 20 mm gap range. The second is the NdFeB based U50II undulator of 50 mm period length with 20 number of periods. Hall probe results are described. A short description of the measurement plan of the undulator on the pulsed wire bench and stretched wire bench is described.

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reference for this paper ※ https://doi.org/10.18429/JACoW-FEL2019-WEP085

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

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WEP086

Capabilities of Terahertz Super-Radiance from Electron Bunches Moving in Micro-Undulators

electron, radiation, GUI, laser

517

N. Balal, V.L. Bratman, A. Friedman, Yu. Lurie
Ariel University, Ariel, Israel
V.L. Bratman
IAP/RAS, Nizhny Novgorod, Russia

Funding: This work was supported by the Israeli Ministry of Science, Technology and Space and by the Russian Foundation for Basic Research, grant No. 16-02-00794.
An available frequency range of coherent radiation from ps bunches with high charge and moderate particle energy significantly enhances if one uses a micro-undulator with a high transverse field. Such an undulator can be implemented by redistributing a strong uniform magnetic field by a helical ferromagnetic or copper insertion. According to simulations and experiments with prototypes, a steel helix with a period of (8-10) mm and an inner diameter of (1.5-2) mm inserted in the 3T-field of solenoid can provide an undulator field with an amplitude of 0.6 T. Using a hybrid system with a permanently magnetized structure can increase this value up to 1.1 T. The necessary steel helices can be manufactured on the machine, assembled from steel wires, formed from powder, or 3D - printed. Simulations based on the WB3D code demonstrate that using such undulators with the length of (30-40) cm enable single-mode super-radiance from bunches with energy of 6 MeV, charge of 1 nC and duration of 2 ps moving in an over-sized waveguide in frequency range of 3-5 THz. The calculated efficiency of such process is (2-4)% that many times exceeds efficiency for short bunches of the same initial density.

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reference for this paper ※ https://doi.org/10.18429/JACoW-FEL2019-WEP086

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paper received ※ 14 August 2019 paper accepted ※ 28 August 2019 issue date ※ 05 November 2019

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WEP089

Pulse Energy Measurement at the SXFEL

FEL, 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

FEL, 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

radiation, FEL, 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

FEL, 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

FEL, 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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WEP097

Operational Model of the Athos Undulator Beamline

polarization, operation, background, MMI

538

C. Kittel, M. Calvi, X. Liang, T. Schmidt
PSI, Villigen PSI, Switzerland
N.J. Sammut
University of Malta, Information and Communication Technology, Msida, Malta

Athos, the new Soft X-ray beamline of SwissFEL, operates 16 Apple X undulators and 15 compact chicanes to implement novel lasing schemes. With the data available after the end of the magnetic measurement campaign (middle 2020), a self-consistent set of equations will be used to summarise all the relevant properties of those devices to start their commissioning. The analytical approach planned will be discussed in great detail and tested with the preliminary experimental data available. Finally, the accuracy of this approach will be evaluated and critically compared to the requirements of the new FEL beamline.

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reference for this paper ※ https://doi.org/10.18429/JACoW-FEL2019-WEP097

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

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WEP098

Advanced Operational Models of the Apple X Undulator

operation, polarization, site, photon

541

X. Liang, M. Calvi, C. Kittel, T. Schmidt
PSI, Villigen PSI, Switzerland
N.J. Sammut
University of Malta, Information and Communication Technology, Msida, Malta

Athos is a new soft X-ray beamline at SwissFEL, where the Apple X type undulators will be equipped. These devices are flexible to produce light in different polarization modes. An adequate magnetic field model is required for the operation of undulator. The undulator deflection parameter K and its gradient are calculated starting from the Fourier series of the magnetic field. In the classical parallel and anti-parallel operational modes - respectively elliptical and linear modes, the variation of the magnetic field as well as its parameters are evaluated by computer modeling. The results are compared to the magnetic measurements of the first Apple X prototype.

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reference for this paper ※ https://doi.org/10.18429/JACoW-FEL2019-WEP098

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paper received ※ 27 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

polarization, electron, FEL, 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

FEL, 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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reference for this paper ※ https://doi.org/10.18429/JACoW-FEL2019-WEP101

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

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WEP107

Polarizing Afterburner for the LCLS-II Undulator Line

radiation, electron, polarization, FEL

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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reference for this paper ※ https://doi.org/10.18429/JACoW-FEL2019-WEP107

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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

alignment, photon, FEL, 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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reference for this paper ※ https://doi.org/10.18429/JACoW-FEL2019-WED01

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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

operation, FEL, 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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reference for this paper ※ https://doi.org/10.18429/JACoW-FEL2019-WED02

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

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THP002

Beam Based Alignment in all Undulator Beamlines at European XFEL

FEL, 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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THP009

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

radiation, simulation, space-charge, FEL

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

FEL, electron, laser, septum

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, FEL

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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reference for this paper ※ https://doi.org/10.18429/JACoW-FEL2019-THP011

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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, FEL, 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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THP024

Spontaneous Coherent Radiation of Stabilized Dense Electron Bunches

electron, radiation, cyclotron, GUI

643

Yu.S. Oparina, V.L. Bratman, A.V. Savilov
IAP/RAS, Nizhny Novgorod, Russia
N. Balal, Yu. Lurie
Ariel University, Ariel, Israel

Funding: The work is supported by Russian Foundation for Basic Research Project 18-32-00351, 18-02-00765
Modern sources of dense electron beams allow the formation of compact sources of dense electron bunches with energies of 3-6 MeV, ps pulse durations, and charges of up to 1 nC. Such bunches can be used for the realization of relatively simple and compact powerful terahertz sources based on spontaneous coherent radiation. The power and duration of the process of such type of emission are limited due to an increase in the bunch length under the Coulomb repulsion. This complicates the effective implementation of the regime of spontaneous coherent radiation for dense bunches. Therefore, special methods for stabilization of the length of the operating e-bunch during its motion over a long electron-wave interaction region should be used. We propose several methods of the stabilization based on the axial bunch compression by self-radiated wave fields [1] and by quasi-static Coulomb fields inside a bunch [2]. The latter takes place in the case of the motion of electrons through the undulator in the "negative-mass" regime, when the Coulomb field inside the bunch leads not to repulsion of electrons but to their mutual attraction.
[1] I. V. Bandurkin, Yu. S. Oparina and A. V. Savilov, Appl. Phys. Lett. vol 110, p. 263508, 2017
[2] N. Balal, I. V. Bandurkin, V. L. Bratman, E. Magory, and A. V. Savilov, Appl. Phys. Lett. vol. 107, p. 163505, 2015

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paper received ※ 19 August 2019 paper accepted ※ 12 September 2019 issue date ※ 05 November 2019

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THP030

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

laser, FEL, 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, FEL, electron

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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THP036

Microbunch Rotation for Hard X-Ray Beam Multiplexing

quadrupole, focusing, FEL, 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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paper received ※ 24 August 2019 paper accepted ※ 26 August 2019 issue date ※ 05 November 2019

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THP047

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

laser, electron, FEL, 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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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, FEL

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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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

FEL, GUI, radiation, 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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paper received ※ 25 August 2019 paper accepted ※ 28 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

electron, radiation, simulation, FEL

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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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

FEL, target, 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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THP066

XARA: X-Band Accelerator for Research and Applications

FEL, electron, 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

vacuum, alignment, electron, FEL

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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THP071

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

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

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THP073

Status Update for the High Gain High Efficiency TESSA-266 Experiment

quadrupole, laser, electron, experiment

730

Y. Park, D.K. Dang, P.E. Denham, P. Musumeci, N.S. Sudar
UCLA, Los Angeles, USA
R.B. Agustsson, T.J. Campese, I.I. Gadjev, A.Y. Murokh
RadiaBeam, Los Angeles, California, USA
C.C. Hall, S.D. Webb
RadiaSoft LLC, Boulder, Colorado, USA
Y. Sun, A. Zholents
ANL, Lemont, Illinois, USA

Funding: DOE grant No. DE-SC0009914 and DE-SC0018559
Tapering Enhanced Stimulated Superradiant Amplification (TESSA) allows to increase the efficiency of Free Electron Laser (FEL) based radiation generation from ~0.1% to 10% by using intense seed laser pulses, strongly tapered undulators and prebunched electron beams [1]. Initial results validating this method have already been obtained at 10 µm wavelength at Brookhaven National Laboratory [2]. We will present the design of an experiment to demonstrate the TESSA scheme at high gain and shorter wavelength (266 nm) using the APS injector linac at Argonne National Labor-atory (ANL) to obtain conversion efficiency of up to 10%. Undulator and focusing lattice design, as well as beam dynamics and diagnostics for this experiment will be discussed. An extension of the experiment to include the possibility of multi-bunch linac operation and an optical cavity around the undulator to operate in the TESSO regime will also be presented [3].
[1] J. Duris et al., New J. Phys. 17 063036 (2015)
[2] N Sudar et al., Physical review letters, 117, 174801 (2016)
[3] J. Duris et al., Physical Review Accelerators and Beams 21, 080705 (2018)

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

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THP074

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

FEL, electron, laser, free-electron-laser

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

FEL, linac, electron, 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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THP084

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

FEL, linac, simulation, experiment

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

FEL, 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, laser, FEL, 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

FEL, controls, photon, operation

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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reference for this paper ※ https://doi.org/10.18429/JACoW-FEL2019-THD03

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

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FRA02

LCLS-II - Status and Upgrades

linac, electron, operation, photon

772

A. Brachmann, M. Dunham, J.F. Schmerge
SLAC, Menlo Park, California, USA

Funding: This work is supported by the U.S. Department of Energy, Office of Science, under Contract No. DE-AC02-76SF00515.
The LCLS-II FEL is under construction at the SLAC National Accelerator Laboratory. This facility is based on a superconducting accelerator, providing a cw e^- beam of 4 GeV at ~1 MHz. This beam drives two variable gap undulator (VGU) beam lines to generate photons in the soft and hard X-ray regime. High repetition rate photon beams will be available up to ~5 keV. The normal conducting accelerator will remain in operation, delivering milli-joule pulses up to ~20 keV for LCLS science. We anticipate to start the LCLS user program in the spring of 2020 using the new undulator systems. Superconducting accelerator operation will start in 2021 and will achieve full design-performance over the course of several years. Approximately a quarter of the superconducting accelerator is installed now and the associated cryoplant construction is near completion. The VGU systems will be installed and ready for beam delivery in early 2020. We will report on the project status, commissioning and ramp-up plans to achieve design performance and discuss plans to take advantage of the new facilities potential including our longer term strategy to extend the capability of SLAC’s LCLS FEL facility.

Slides FRA02 [24.207 MB]

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reference for this paper ※ https://doi.org/10.18429/JACoW-FEL2019-FRA02

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paper received ※ 04 August 2019 paper accepted ※ 27 August 2019 issue date ※ 05 November 2019

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FRA03

FLASH - Status and Upgrades

laser, electron, FEL, 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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reference for this paper ※ https://doi.org/10.18429/JACoW-FEL2019-FRA03

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

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