FEL2019 - List of Keywords (radiation)

Paper	Title	Other Keywords	Page
MOA01	Riding the FEL Instability (Dedicated to Alberto Renieri)	electron, laser, storage-ring, free-electron-laser	1
	G. Dattoli ENEA C.R. Frascati, Frascati (Roma), Italy M.-E. Couprie SOLEIL, Gif-sur-Yvette, France C. Pellegrini SLAC, Menlo Park, California, USA
	The Free Electron Laser (FEL) operation, like that of any Free Electron source of coherent radiation, is associated with the onset of an instability. The interplay between the FEL and other instabilities, affecting the beam, is one of the interesting aspects of the associated dynamics. It involves issues of practical interest (Renieri Limit in Storage Ring FELs, suppression of instabilities like saw-tooth and synchrotron…). The paper reviews these problems and offers an overview of the scientific contribution of Alberto Renieri to the FEL from this perspective.
	Slides MOA01 [5.143 MB]
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-FEL2019-MOA01
About •	paper received ※ 26 August 2019 paper accepted ※ 09 September 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	FEL, undulator, electron, experiment	38
	P. Boonpornprasert, G.Z. Georgiev, G. Koss, M. Krasilnikov, X. Li, F. Mueller, A. Oppelt, S. Philipp, H. Shaker, F. Stephan, T. Weilbach DESY Zeuthen, Zeuthen, Germany Z.G. Amirkhanyan CANDLE SRI, Yerevan, Armenia
	The Photo Injector Test Facility at DESY in Zeuthen (PITZ) has been proposed as a suitable facility for research and development of an accelerator-based THz source prototype for pump-probe experiments at the European XFEL. A proof-of-principle experiment to generate THz SASE FEL radiation by using an LCLS-I undulator driven by an electron bunch from the PITZ accelerator has been planned and studied. The undulator is foreseen to be installed downstream from the current PITZ accelerator, and an extension of the accelerator tunnel is necessary. Radiation shielding for the extended tunnel was designed, and construction works are finished. Design of the extended beamline is ongoing, not only for this experiment but also for other possible experiments. Components for the extended beamline, including magnets for beam transport, a chicane bunch compressor, electron beam diagnostics devices, and THz radiation diagnostics devices have been studied. An overview of these works will be presented in this paper.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-FEL2019-TUP001
About •	paper received ※ 20 August 2019 paper accepted ※ 28 August 2019 issue date ※ 05 November 2019
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TUP003	Design of a Magnetic Bunch Compressor for the THz SASE FEL Proof-of-Principle Experiment at PITZ	FEL, dipole, experiment, undulator	45
	H. Shaker, P. Boonpornprasert, G.Z. Georgiev, G. Koss, M. Krasilnikov, X. Li, A. Lueangaramwong, F. Mueller, A. Oppelt, S. Philipp, F. Stephan, G. Vashchenko, T. Weilbach DESY Zeuthen, Zeuthen, Germany
	For pump-probe experiments at the European XFEL, a THz source is required to produce intense THz pulses at the same repetition rate as the X-ray pulses from XFEL. Therefore, an accelerator-based THz source with identical electron source as European XFEL was suggested and proof-of-principle experiments utilizing an LCLS I undulator will be performed at the Photo Injector Test Facility at DESY in Zeuthen (PITZ). The main idea is to use a 4nC beam for maximum SASE radiation but to allow different radiation regimes a magnetic bunch compressor can be used. This helps e.g. to reduce the saturation length inside the undulator and also to study super-radiant THz radiation. In this paper a design of a chicane type magnetic bunch compressor using HERA corrector magnets is presented.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-FEL2019-TUP003
About •	paper received ※ 20 August 2019 paper accepted ※ 27 August 2019 issue date ※ 05 November 2019
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TUP004	A Superradiant THz Undulator Source for XFELs	undulator, FEL, electron, 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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TUP007	Experience with the Superradiant THz User Facility Driven by a Quasi-CW SRF Accelerator at ELBE	detector, electron, SRF, experiment	56
	M. Bawatna, B.W. Green HZDR, Dresden, Germany
	Instabilities in beam and bunch parameters, such as bunch charge, beam energy or changes in the phase or amplitude of the accelerating field in the RF cavities can be the source of noise in the various secondary sources driven by the electron beam. Bunch charge fluctuations lead to intensity instabilities in the super-radiant THz sources. The primary electron beam driving the light sources has a maximum energy of 40 MeV and a maximum current of 1.6 mA. Depending on the mode of operation required, there are two available injectors in use at ELBE. The first is the thermionic injector, which is used for regular operating modes and supports repetition rates up to 13 MHz and bunch charges up to 100 pC. The second is the SRF photo-cathode injector, which is used for experiments that may require lower emittance or higher bunch charges of up to 1 nC. It has a maximum repetition rate of 13 MHz, which can be adjusted to lower rates if desired, also including different macro pulse modes of operation. In this contribution, we will present our work in the pulse-resolved intensity measurement that allows for correction of intensity instabilities.
	Poster TUP007 [0.658 MB]
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-FEL2019-TUP007
About •	paper received ※ 20 August 2019 paper accepted ※ 27 August 2019 issue date ※ 05 November 2019
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TUP008	Concept of High-Power CW IR-THz Source for the Radiation Source Elbe Upgrade	undulator, electron, 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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TUP009	Integration of an XFELO at the European XFEL Facility	FEL, electron, simulation, cavity	62
	P. Rauer, I. Bahns, W. Hillert, J. Roßbach University of Hamburg, Institut für Experimentalphysik, Hamburg, Germany W. Decking DESY, Hamburg, Germany H. Sinn EuXFEL, Schenefeld, Germany
	Funding: Work supported by BMBF (FKZ 05K16GU4) An X-ray free-electron laser oscillator (XFELO) is a fourth generation X-ray source promising radiation with full three dimensional coherence, nearly constant pulse to pulse stability and more than an order of magnitude higher peak brilliance compared to SASE FELs. Proposed by Kim et al. in 2008 [1] an XFELO follows the concept of circulating the light in an optical cavity - as known from FEL oscillators in longer wavelength regimes - but uses Bragg reflecting crystals instead of classical mirrors. With the new European X-ray Free-Electron Laser (XFEL) facility recently gone into operation, the realization of an XFELO with radiation in the Angstrom regime seems feasible. Though, the high thermal load of the radiation on the cavity crystals, the high sensibility of the Bragg-reflection on reflection angle and crystal temperature as well as the very demanding tolerances of the at least 60 m long optical resonator path pose challenges which need to be considered. In this work these problems shall be summarized and results regarding the possible integration of an XFELO at the European XFEL facility will be presented. [1] K.-J. Kim, Y. Shvyd’ko and S. Reiche, Phys. Rev. Lett. 100 (2008), 244802.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-FEL2019-TUP009
About •	paper received ※ 20 August 2019 paper accepted ※ 29 August 2019 issue date ※ 05 November 2019
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TUP012	Smith-Purcell Radiation Emitted by Pico-second Electron Bunches from a 30 keV Photo-Electron Gun	electron, experiment, laser, gun	66
	M.R. Asakawa, S. Yamaguchi Kansai University, Osaka, Japan
	In this paper, an experiment to generate Smith-Purcell radiation using pico-second electron bunches is reported. The electron bunch was produced by a DC 30 keV photo-electron electron gun driven by a 100 fs Ti:sapphire laser. The charge of the bunch varied from 1 pC to 300 pC by changing the laser power. Smith-Purcell radiation experiment was performed with the central part of the entire electron bunch. Estimation of pulsewidth of the bunch based on the envelope equation showed that the pulsewidth of the bunch at the anode electrode increased from 0.8 ps to 3.2 ps as the bunch charge increase from 0.1 pC to 11 pC. Such electron bunch was traveled along the surface of the metallic grating with a period of 2 mm. The radiation wavelength was estimated to be 4 mm at an obserbation angle of 10 degree. The radiation power was measured by a bolometer and quadraticallly increased with the bunch charge. Numerical simulation of this experiment indicated the enhancement of the harmonic components of the radiation. We are now constructing a THz-TDS system to measure the time-trace of the electric field of the radiation.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-FEL2019-TUP012
About •	paper received ※ 14 August 2019 paper accepted ※ 27 August 2019 issue date ※ 05 November 2019
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TUP014	Crossed-Undulator Configuration for Variable Polarized THz Source	undulator, 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	electron, FEL, undulator, laser	73
	D. Wu, T.H. He, L.B. Li, M. Li, P. Li, X. Luo, Q. Pan, L.J. Shan, X. Shen, H. Wang, J. Wang, D.X. Xiao, L.G. Yan, P. Zhang, K. Zhou CAEP/IAE, Mianyang, Sichuan, People’s Republic of China
	China Academy of Engineering Physics terahertz free electron laser (CAEP THz FEL, CTFEL) is the first THz FEL oscillator in China. CTFEL spectrum covers from 0.7 THz to 4.2 THz. However, there are still many applications requiring lower frequency. The super-radiation of the ultra-short electron beam bunches could generate ultra-fast, carrier-envelope-phase-stable, and high-field terahertz. The coherent diffraction/transition radiation (CDR/CTR) and coherent undulator radiation (CUR) can be also synchronized naturally. In this paper, the dynamic and the design of the super-radiation are introduced. The main parameters of the CDR/CTR and CUR are also discussed. A multi-color pump-probe system based on super-radiation is also proposed. Work supported by National Natural Science Foundation of China with grant (11575264, 11605190 and 11805192), Innovation Foundation of CAEP with grant (CX2019036, CX2019037)
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-FEL2019-TUP015
About •	paper received ※ 20 August 2019 paper accepted ※ 27 August 2019 issue date ※ 05 November 2019
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TUP017	Terahertz FEL Simulation in PAL XFEL	FEL, electron, simulation, undulator	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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TUP018	Superradiant Emission of Electron Bunches Based on Cherenkov Excitation of Surface Waves in 1D and 2D Periodical Lattices: Theory and Experiments	electron, GUI, experiment, simulation	80
	A. Malkin, N.S. Ginzburg, A. Sergeev, I.V. Zheleznov, I.V. Zotova IAP/RAS, Nizhny Novgorod, Russia M.I. Yalandin RAS/IEP, Ekaterinburg, Russia V.Yu. Zaslavsky UNN, Nizhny Novgorod, Russia
	Funding: The work was supported by RFBR grant no. 17-08-01072 In recent years, significant progress was achieved in generation of high-power ultrashort microwave pulses based on superradiance (SR) of electron bunches extended in the wavelength scale. In this process, coherent emission from the entire volume of the bunch occurs due to the development of microbunching and slippage of the wave with respect to electrons. An obvious method for generation of high-power sub-THz radiation is the implementation of oversized periodical slow-wave structures where evanescent surface waves can be excited. We report of the experiments on Cherenkov generation of 150 ps SR pulses with a central frequency of 0.14 THz, and an extremely high peak power up to 70 MW. In order to generate spatially coherent radiation in shorter wavelength ranges (including THz band) in strongly oversized waveguiding systems, we propose a slow wave structure with double periodic corrugation (2D SWS). Using the quasi-optical theory and PIC simulations, we demonstrate the applicability of such 2D SWS and its advantages against traditional 1D SWS. Proof of principle experiments on observation G-band Cherenkov SR in 2D SWS are currently in progress.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-FEL2019-TUP018
About •	paper received ※ 20 August 2019 paper accepted ※ 27 August 2019 issue date ※ 05 November 2019
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TUP021	Development of Powerful Long-Pulse Terahertz Band FELs Based on Linear Induction Accelerators	electron, FEL, simulation, feedback	91
	V.Yu. Zaslavsky, N.S. Ginzburg, A. Malkin, N.Yu. Peskov, A. Sergeev IAP/RAS, Nizhny Novgorod, Russia A.V. Arzhannikov, E.S. Sandalov, S.L. Sinitsky, D.I. Skovorodin, A.A. Starostenko BINP SB RAS, Novosibirsk, Russia
	Funding: This work was supported by the Russian Scientific Foundation (RSCF), grant No. 19-12-00212. The paper is devoted to development of high-power long-pulse THz-band FELs based on new generation of linear induction accelerators which have been elaborated recently at Budker Institute (Novosibirsk). These accelerators generate microsecond electron beams with current at kA-level and energy of 2 to 5 MeV (with a possibility to increase electrons energy up to 20 MeV). Based on this beam, we initiated a new project of multi-MW long-pulse FEL operating in the frequency range of 1 to 10 THz using a wiggler period of 3 to 6 cm. For this FEL oscillator, we suggest a hybrid planar two-mirror resonator consisting of an upstream highly selective advanced Bragg reflector and a downstream weakly reflecting conventional Bragg reflector. Simulations demonstrate that the advanced Bragg reflector based on coupling of propagating and quasi-cutoff waves ensures the mode control at the values of the gap between the corrugated plates forming such resonator up to 20 wavelengths. Simulations of the FEL driven by electron beam generated by the LIU¿2 in the frame of both averaged approach and 3D PIC code demonstrate that the THz radiation power can reach the level of 10 to 20 MW.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-FEL2019-TUP021
About •	paper received ※ 28 August 2019 paper accepted ※ 28 August 2019 issue date ※ 05 November 2019
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TUP023	Analytical and Numerical Comparison of Different Approaches to the Description of SASE in High Gain FELs	FEL, simulation, undulator, bunching	94
	O.A. Shevchenko, N.A. Vinokurov BINP SB RAS, Novosibirsk, Russia N.A. Vinokurov NSU, Novosibirsk, Russia
	Correlation function theory which has been developed recently gives rigorous statistical description of the SASE FEL operation. It directly deals with the values averaged over many shots. There are two other approaches which are based either on Vlasov equation or on direct solution of particle motion equations. Both of them use random functions which relate to single shot. To check the validity of these three approaches it might be interesting to compare them with each other. In this paper we present the results of such comparison obtained for the 1-D FEL model. We show that two-particle correlation function approximation is equivalent to the quasilinear approximation of the Vlasov equation approach. These two approximations are in a good agreement with the results of direct solution of particle motion equations at linear and early saturation stages. To obtain this agreement at strong saturation high order harmonics in Vlasov equation have to be taken into account which corresponds to taking into account of three and more particle correlations in the correlation function approach.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-FEL2019-TUP023
About •	paper received ※ 19 August 2019 paper accepted ※ 25 August 2019 issue date ※ 05 November 2019
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TUP024	Electronic Modulation of the FEL-Oscillator Radiation Power Driven by ERL	FEL, electron, experiment, controls	98
	O.A. Shevchenko, E.V. Bykov, Ya.V. Getmanov, S.S. Serednyakov, S.V. Tararyshkin BINP SB RAS, Novosibirsk, Russia M.V. Fedin, A.R. Melnikov, S.L. Veber International Tomography Center, SB RAS, Novosibirsk, Russia Ya.V. Getmanov, S.S. Serednyakov NSU, Novosibirsk, Russia
	FEL oscillators usually operate in CW mode and produce periodic train of radiation pulses but some user experiments require modulation of radiation power. Conventional way to obtain this modulation is using of mechanical shutters but it cannot provide very short switching time and may lead to decreasing of the radiation beam quality. Another way could be based on the electron beam current modulation but it cannot be used in the ERL. We propose a simple way of fast control of the FEL lasing which is based on periodic phase shift of electron bunches with respect to radiation stored in optical cavity. The phase shift required to suppress lasing is relatively small and it does not change significantly repetition rate. This approach has been realized at NovoFEL facility. It allows to generate radiation macropulses of desirable length down to several microseconds (limited by quality factor of optical cavity and FEL gain) which can be synchronized with external trigger. We present detailed description of electronic power modulation scheme and discuss the results of experiments.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-FEL2019-TUP024
About •	paper received ※ 20 August 2019 paper accepted ※ 27 August 2019 issue date ※ 05 November 2019
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TUP032	Regenerative Amplification for a Hard X-Ray Free-Electron Laser	FEL, cavity, electron, undulator	118
	G. Marcus, Y. Ding, Y. Feng, A. Halavanau, Z. Huang, J. Krzywiński, J.P. MacArthur, R.A. Margraf, T.O. Raubenheimer, D. Zhu SLAC, Menlo Park, California, USA V. Fiadonu Santa Clara University, Santa Clara, California, USA
	Funding: This work was supported by the Department of Energy, Laboratory Directed Research and Development program at SLAC National Accelerator Laboratory, under contract DE-AC02-76SF00515. An X-ray regenerative amplifier FEL (XRAFEL) utilizes an X-ray crystal cavity to provide optical feedback to the entrance of a high-gain undulator. An XRAFEL system leverages gain-guiding in the undulator to reduce the cavity alignment tolerances and targets the production of longitudinally coherent and high peak power and brightness X-ray pulses that could significantly enhance the performance of a standard single-pass SASE amplifier. The successful implementation of an X-ray cavity in the XRAFEL scheme requires the demonstration of X-ray optical components that can either satisfy large output coupling constraints or passively output a large fraction of the amplified coherent radiation. Here, we present new schemes to either actively Q-switch a diamond Bragg crystal through lattice constant manipulation or passively output couple a large fraction of the stored cavity radiation through controlled FEL microbunch rotation. A beamline design study, cavity stability analysis, and optimization will be presented illustrating the performance of potential XRAFEL configurations at LCLS-II/-HE using high-fidelity simulations.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-FEL2019-TUP032
About •	paper received ※ 24 August 2019 paper accepted ※ 26 August 2019 issue date ※ 05 November 2019
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TUP036	A Waveguide-Based High Efficiency Super-Radiant FEL Operating in the THz Regime	FEL, GUI, electron, undulator	127
	P. Musumeci, A.C. Fisher UCLA, Los Angeles, California, USA A. Gover University of Tel-Aviv, Faculty of Engineering, Tel-Aviv, Israel E.A. Nanni, E.J. Snively SLAC, Menlo Park, California, USA S.B. van der Geer Pulsar Physics, Eindhoven, The Netherlands
	Funding: DOE grant No. DE-SC0009914 and NSF grant PHY-1734215 In this paper we describe a novel self-consistent 3D simulation approach for a waveguide FEL operating in the zero-slippage regime to generate high power THz radiation. In this interaction regime, the phase and group velocity of the radiation are matched to the relativistic beam traveling in the undulator achieving long interaction lengths. Our numerical approach is based on expanding the existing 3D particle tracking code GPT (General Particle Tracer) to follow the interaction of the particles in the beam with the electromagnetic field modes of the waveguide. We present two separate studies: one for a case which was benchmarked with experimental results and another one for a test case where, using a longer undulator and larger bunch charge, a sizable fraction of the input beam energy can be extracted and converted to THz radiation. The model presented here is an important step in the development of the zero-slippage FEL scheme as a source for high average and peak power THz radiation.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-FEL2019-TUP036
About •	paper received ※ 20 August 2019 paper accepted ※ 29 August 2019 issue date ※ 05 November 2019
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TUP037	Optimization of the Transverse Gradient Undulator (TGU) for Application in a Storage Ring Based XFELO	electron, storage-ring, emittance, undulator	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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TUP038	Axial Symmetry in Spontaneous Undulator Radiation for XFELO Two-Bunch Experiment	FEL, electron, experiment, laser	134
	Y.S. Li University of Chicago, Chicago, Illinois, USA K. Kim, R.R. Lindberg ANL, Lemont, Illinois, USA
	Funding: U.S. DOE, Office of Science, Office of BES, under Contract No. DE-AC02-06CH11357 and National Science Foundation under Award No. PHY-1549132, the Center for Bright Beams. A well known discrepancy exists between 2D and 3D FEL simulation codes with respect to the radiation field intensity prior to the exponential gain regime [1]. This can be qualitatively explained by the fact that the 3D field representation preserves many more modes than does the axisymmetric field solved for by a 2D code. In this paper, we seek to develop an analytical model that quantifies this difference. We begin by expanding the spontaneous undulator radiation field as a multipole series, whose lowest order mode is axisymmetric. This allows us to calculate the difference in predicted intensity. Next, we confirm these results with numerical calculation and existing FEL codes GINGER and GENESIS. Finally, we discuss the implications of this study with respect to the XFELO two-bunch experiment to be conducted at LCLS-II. [1] Z. Huang and K.-J. Kim, "Review of X-ray free-electron laser theory", Phys. Rev. ST-AB, vol. 10, p. 034801, 2007.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-FEL2019-TUP038
About •	paper received ※ 19 August 2019 paper accepted ※ 28 August 2019 issue date ※ 05 November 2019
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TUP041	X-cos SCILAB Model for Simulation of Intensity and Gain of Planar Undulator Radiation	undulator, simulation, electron, 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	undulator, electron, 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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TUP051	Plasma Accelerator Driven Coherent Spontaneous Emission	electron, FEL, bunching, undulator	157
	B.M. Alotaibi, R. Altuijri PNU, Riyadh, Kingdom of Saudi Arabia B.M. Alotaibi, R. Altuijri, A.F. Habib, B. Hidding, B.W.J. MᶜNeil, P. Traczykowski USTRAT/SUPA, Glasgow, United Kingdom A.F. Habib, B. Hidding, B.W.J. MᶜNeil, P. Traczykowski Cockcroft Institute, Warrington, Cheshire, United Kingdom
	Plasma accelerators [1] are a potentially important source of high energy, low emittance electron beams with high peak currents generated within a relatively short distance. As such, they may have an important application in the driving of coherent light sources such as the Free Electron Laser (FEL) which operate into the X-ray region [2]. While novel plasma photocathodes [3] may offer orders of magnitude improvement to the normalized emittance and brightness of electron beams compared to Radio Frequency-driven accelerators, a substantial challenge is the energy spread and chirp of beams, which can make FEL operation impossible. In this paper it is shown that such an energy-chirped, ultrahigh brightness electron beam, with dynamically evolving current profile due to ballistic bunching at moderate energies, can generate significant coherent radiation output via the process of Coherent Spontaneous Emission (CSE)[4]. While this CSE is seen to cause some FEL-induced electron bunching at the radiation wavelength, the dynamic evolution of the energy chirped pulse dampens out any high-gain FEL interaction. [1] E. Esary et al., Reviews of Modern Physics p. 1229 (2009). [2] B. W. J. McNeil and N. R. Thompson, 2010 Nat. Photon.4 814-21 [3] B. Hidding et al., 2012 Phys. Rev. Lett. 108 035001 [4] L. T. Campbell and B. W. J. McNeil, 2012, in Proc. FEL2012
	Poster TUP051 [1.401 MB]
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-FEL2019-TUP051
About •	paper received ※ 20 August 2019 paper accepted ※ 27 August 2019 issue date ※ 05 November 2019
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TUP053	An Investigation of Possible Non-Standard Photon Statistics in a Free-Electron Laser I: Experiment	photon, FEL, experiment, cavity	161
	J.-W. Park University of Hawaii, Honolulu,, USA K.-J. Kim, R.R. Lindberg ANL, Lemont, Illinois, USA
	Funding: Work supported by U.S. DOE, Office of Science, Office of BES, under Award No. DE-SC0018428. It was reported that the photon statistics of the seventh coherent spontaneous harmonic radiation of the MARK III FEL was sub-Poissonian [1], which concludes that Fano factor F (the ratio of photon number variance to the average photon number) is less than unity. Whether FEL light exhibits such non-standard behavior is an important issue; if it does, our understanding of the FEL needs to be radically modified. In this paper, we re-examine the analyses of experimental data in Ref. [1]. We find that the observed value of F could be explained within the standard FEL theory if one combines the detector dead time effect with photon clustering arising from the FEL gain. We propose an improved experiment for a more definitive measurement of the FEL photon statistics. [1] T. Chen and J.M. Madey, J. Phys. Rev. Lett. 86, 5906 (2001).
	Poster TUP053 [0.929 MB]
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-FEL2019-TUP053
About •	paper received ※ 21 August 2019 paper accepted ※ 12 September 2019 issue date ※ 05 November 2019
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TUP054	An Investigation of Possible Non-Standard Photon Statistics in a Free-Electron Laser II: Theory	electron, photon, FEL, laser	165
	J.-W. Park University of Hawaii, Honolulu,, USA K.-J. Kim, R.R. Lindberg ANL, Lemont, Illinois, USA K.-J. Kim University of Chicago, Chicago, Illinois, USA
	Funding: Work supported by U.S. DOE, Office of Science, Office of BES, under Award No. DE-SC0018428. In this paper we explore whether we can at present find a theoretical basis for non-standard, sub-Poissonian photon statistics in the coherent spontaneous harmonic radiation of an FEL as was claimed to have been measured with the Mark III FEL [1]. We develop a one dimensional quantum FEL oscillator model of the harmonic radiation in the linear gain regime to calculate the photon statistics. According to our study, it seems unlikely that the photon statistics for an FEL oscillator starting from the noise could be sub-Poissonian. [1] T. Chen and J.M. Madey, J. Phys. Rev. Lett. 86, 5906 (2001).
	Poster TUP054 [0.386 MB]
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-FEL2019-TUP054
About •	paper received ※ 21 August 2019 paper accepted ※ 16 September 2019 issue date ※ 05 November 2019
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TUP057	Analysis of Parameter Space of Soft X-Ray Free Electron Laser at the European XFEL Driven by High and Low Energy Electron Beam	undulator, FEL, electron, 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, photon, electron, undulator	180
	V. Balandin, B. Beutner, F. Brinker, W. Decking, M. Dohlus, L. Fröhlich, U. Jastrow, R. Kammering, T. Limberg, D. Nölle, M. Scholz, A.A. Sorokin, K.I. Tiedtke, M.V. Yurkov, I. Zagorodnov DESY, Hamburg, Germany U. Boesenberg, W. Freund, J. Grünert, A. Koch, N.G. Kujala, J. Liu, Th. Maltezopoulos, M. Messerschmidt, I. Petrov, L. Samoylova, H. Sinn EuXFEL, Schenefeld, Germany
	North branch of the European XFEL, SASE1, produced first light on May 3rd, 2017, and XFEL operation has been gradually improved then. First characterization of the photon beam has been performed in July / August 2017, just before an official starting date of user experiments (September 1st, 2017). Energy of the electron beam was 14 GeV, bunch charge was 500 pC, photon energy was 9.3 keV. With photon diagnostics available at that time (X-ray gas monitor (XGM) and FEL imager) we measured the gain curve and traced evolution of the FEL radiation mode along the undulator. An important conclusion is that experimental results demonstrate reasonable agreement with baseline parameters. Developed techniques of the photon beam characterization also provided solid base for identification of the problems and means for improving SASE FEL tuning and operation.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-FEL2019-TUP058
About •	paper received ※ 20 August 2019 paper accepted ※ 27 August 2019 issue date ※ 05 November 2019
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TUP059	Influence of Energy Chirp in the Electron Beam and Undulator Tapering on Spatial Properties of the Radiation From Seeded and SASE FEL	FEL, undulator, 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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TUP062	Two Colors at the SASE3 Line of the European XFEL: Project Scope and First Measurements	FEL, electron, photon, experiment	195
	S. Serkez, G. Geloni, N. Gerasimova, J. Grünert, S. Karabekyan, A. Koch, J. Laksman, Th. Maltezopoulos, T. Mazza, M. Meyer, S. Tomin EuXFEL, Schenefeld, Germany W. Decking, L. Fröhlich, V. Kocharyan, Y.A. Kot, E. Saldin, E. Schneidmiller, M. Scholz, M.V. Yurkov, I. Zagorodnov DESY, Hamburg, Germany M. Huttula University of Oulu, Oulu, Finland E. Kukk University of Turku, Turku, Finland
	The European XFEL is a high-repetition rate facility that generates high-power SASE radiation pulses in three beamlines. A joint upgrade project, with Finnish universities, to equip the SASE3 beamline with a chicane has been recently approved to generate two SASE pulses with different photon energies and temporal separation. In this work we report the status of the project, its expected performance, and recent experimental results. Additionally, we discuss methods to diagnose the properties of the generated radiation.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-FEL2019-TUP062
About •	paper received ※ 20 August 2019 paper accepted ※ 29 August 2019 issue date ※ 05 November 2019
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TUP065	Optimization of a Coherent Undulator Beamline for New Advanced Synchrotron Light Source in Korea	undulator, electron, synchrotron, FEL	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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TUP072	Orbital Angular Momentum from SASE	electron, quadrupole, FEL, undulator	218
	J.F. Morgan, B.W.J. MᶜNeil USTRAT/SUPA, Glasgow, United Kingdom B.W.J. MᶜNeil, J.F. Morgan, B.D. Muratori, P.H. Williams, A. Wolski Cockcroft Institute, Warrington, Cheshire, United Kingdom B.D. Muratori, P.H. Williams STFC/DL/ASTeC, Daresbury, Warrington, Cheshire, United Kingdom A. Wolski The University of Liverpool, Liverpool, United Kingdom
	Radiation with orbital angular momentum, OAM, has many applications such as in imaging systems and microscopic tweezers [1]. The feasibility of generating light with OAM in a free electron laser, FEL, from amplified shot noise in an electron beam is investigated using the FEL simulation code Puffin [2]. This may allow generation of OAM radiation at shorter wavelengths than currently available, as well as the opportunity to incorporate the technique with other SASE manipulation schemes such as mode locking [3]. [1] A. M. Yao and M. J. Padgett, Adv. Opt. Photon. 3, 161(2011) [2] L. T. Campbell and B. W. J. McNeil, Phys. Plasmas. 19, 093119(2012) [3] D. J. Dunning, B. W. J. McNeil, and N. R. Thompson, Phys. Rev. Lett. 110, 104801(2013)
	Poster TUP072 [1.311 MB]
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-FEL2019-TUP072
About •	paper received ※ 20 August 2019 paper accepted ※ 28 August 2019 issue date ※ 05 November 2019
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TUP073	High-Repetition-Rate Seeding Schemes Using a Resonator-Amplifier Setup	FEL, laser, electron, cavity	222
	S. Ackermann, B. Faatz, V. Grattoni, C. Lechner, G. Paraskaki DESY, Hamburg, Germany G. Geloni, S. Serkez, T. Tanikawa EuXFEL, Schenefeld, Germany W. Hillert University of Hamburg, Institut für Experimentalphysik, Hamburg, Germany
	The spectral and temporal properties of Free-Electron Lasers (FEL) operating on the basis of self-amplified spontaneous emission (SASE) suffer from the stochastic behavior of the start-up process. Several so-called "seeding"-techniques using external radiation fields to overcome this limitation have been proposed and demonstrated. The external seed is usually generated by demanding, high-power laser systems, which are not available with a sufficient laser pulse energy at the high repetition rates of superconducting FEL facilities. In this contribution we discuss several seeding schemes that lower the requirements for the used laser systems, enabling seeded operation at high repetition rates by the means of a resonator-amplifier setup.
	Poster TUP073 [0.521 MB]
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-FEL2019-TUP073
About •	paper received ※ 06 August 2019 paper accepted ※ 29 August 2019 issue date ※ 05 November 2019
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TUP079	Status of the Hard X-Ray Self-Seeding Setup at the European XFEL	FEL, undulator, electron, 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, undulator, 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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TUP088	Numerical Simulations for Generating Fully Coherent Soft X-Ray Free Electron Lasers With Ultra-Short Wavelength	electron, laser, FEL, free-electron-laser	258
	K.S. Zhou, H.X. Deng, B. Liu, D. Wang SARI-CAS, Pudong, Shanghai, People’s Republic of China
	For the fully coherent, ultra-short and high power soft X-rays are becoming key instruments in many different research fields, such as biology, chemistry or physics. However, it’s hard to generate this kind of advanced light source by the conventional lasers, especially for the soft X-rays with ultra-short wavelength because of no suitable reflectors. The external seeded free electron laser (FEL) is considered as one feasible method. Here, we give an example to generate highly temporal coherent soft X-rays with the wavelength 1 nm by the two-stage cascaded schemes. EEHG scheme is used as the first-stage while the HGHG scheme is used as the second-stage.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-FEL2019-TUP088
About •	paper received ※ 20 August 2019 paper accepted ※ 22 October 2019 issue date ※ 05 November 2019
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TUP092	XFEL Third Harmonic Statistics Measurement at LCLS	FEL, photon, undulator, experiment	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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TUD03	Fine and Hyperfine Structure of FEL Emission Spectra	FEL, electron, laser, experiment	276
	V.V. Kubarev, Ya.V. Getmanov, O.A. Shevchenko BINP SB RAS, Novosibirsk, Russia S. Bae, Y.U. Jeong KAERI, Daejon, Republic of Korea
	This paper presents the results of experimental investigations of the fine and hyperfine spectral structures of the Novosibirsk free-electron laser (NovoFEL) and the compact free-electron laser of the Korea Atomic Energy Research Institute (KAERI FEL) by means of the optimal instruments, resonance Fabry-Perot interferometers. The very high coherence of the NovoFEL spectrum was measured in regimes with one pulse circulating inside its optical resonator (the coherence length is 7 km, and the relative width of the hyperfine structure lines is 2E-8) and with total absence of coherence between two circulating pulses, i.e. the fine structure. Sixty pulses circulate simultaneously inside the KAERI FEL optical resonator, and the measured coherence length on average covers ten pulses (the coherence length is 1 m; the relative width of the fine structure lines is 10^-4).
	Slides TUD03 [3.177 MB]
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-FEL2019-TUD03
About •	paper received ※ 16 August 2019 paper accepted ※ 29 August 2019 issue date ※ 05 November 2019
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TUT01	Superradiance and Stimulated-Superradiant Emission of Bunched Electron Beams	electron, wiggler, FEL, undulator	288
	A. Gover, R. Ianconescu University of Tel-Aviv, Faculty of Engineering, Tel-Aviv, Israel C. Emma, P. Musumeci, C. Pellegrini, N.S. Sudar UCLA, Los Angeles, USA A. Friedman Ariel University, Ariel, Israel R. Ianconescu Shenkar College of Engineering and Design, Ramat Gan, Israel
	Funding: We acknowledge support of the Israel Science Foundation and the German Israeli Projects Foundation (DIP). We outline the fundamental processes of coherent radiation emission from a bunched charged particles beam [1]. In contrast to spontaneous emission of radiation from a random electron beam that is proportional to the number of particles N, a pre-bunched electron beam emits spontaneously coherent radiation proportional to N² through the process of (spontaneous) superradiance (SP-SR) (in the sense of Dicke’s [2]). The SP-SR emission of a bunched electron beam can be even further enhanced by a process of stimulated-superradiance (ST-SR) in the presence of a seed injected radiation field. These coherent radiation emission processes are presented in term of a radiation mode expansion model, applied to general free electron radiation schemes: Optical-Klystron, HGHG, EEHG, and coherent THz sources based on synchrotron radiation, undulator radiation or Smith-Purcell radiation. The general model of coherent spontaneous emission is also extended to the nonlinear regime - Tapering Enhanced Stimulated Superradiance (TESSA) [3], and related to the tapered wiggler section of seed-injected FELs. In X-Ray FELs these processes are convoluted with other effects, but they are guidelines for strategies of wiggler tapering efficiency enhancement. [1] A. Gover et al., Rev. Mod. Phys. https://arxiv.org/abs/1810.07566v3 (2019) [2] R. H. Dicke, Physical Review 93, 99 (1954) [3] N. Sudar et al., P.R.L. 117, 174801 (2016)
	Slides TUT01 [11.391 MB]
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-FEL2019-TUT01
About •	paper received ※ 20 August 2019 paper accepted ※ 29 August 2019 issue date ※ 05 November 2019
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WEP012	THz Spectroscopy with MHz Repetition Rates for Bunch Profile Reconstructions at European XFEL	flattop, FEL, electron, undulator	350
	N.M. Lockmann, C. Gerth, B. Schmidt, S. Wesch DESY, Hamburg, Germany
	The European X-ray Free-Electron Laser generates most powerful and brilliant X-ray laser pulses. Exact knowledge about the longitudinal electron bunch profile is crucial for the operation of the linear accelerator as well as for photon science experiments. The only longitudinal diagnostic downstream of the main linac is based on spectroscopy of diffraction radiation (DR). The spectral intensity of the DR in the THz and infrared regime is monitored by a four-staged grating spectrometer and allows non-invasive bunch length characterization based on form factor measurements in the range 0.7 - 60 THz. As the readout and signal shaping electronics of the spectrometer allow MHz readout rates, the longitudinal bunch profile of all bunches inside the bunch train can be characterized non-invasively and simultaneously to FEL operation. In this paper, form factor measurements along the bunch train will be described and presented as well as the resulting reconstructed current profiles.
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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WEP030	All-Fiber Photonic, Ultralow-Noise, Robust Optical and Microwave Signal Generators for FELs and UED	laser, timing, photon, operation	382
	J. Kim, I.J. Jeon, D. Kim, D. Kwon KAIST, Daejeon, Republic of Korea
	Funding: National Research Foundation of Korea (2018R1A2B3001793) and Korea Atomic Energy Research Institute Optical timing and synchronization is becoming a more important and essential element for ultrafast X-ray and electron science. As a result, compact, ultralow-noise, mechanically robust and long-term stable optical and microwave signal generators are highly desirable for future XFELs and UEDs. Here we show that the combination of mode-locked fiber laser and fiber delay-based stabilization method enables the generation of ultralow-noise optical and microwave signals. We show that all-PM fiber lasers can provide excellent mechanical robustness: stable laser operation over >1 hour is maintained even in continuous 1.5 g vibrations [1]. Using a compactly packaged fiber delay as the timing reference, we could stabilize the repetition-rate phase noise of mode-locked lasers down to -100 dBc/Hz and -160 dBc/Hz at 1 Hz and 10 kHz offset frequency, respectively, at 1 GHz carrier, which corresponds to only 1.4 fs rms absolute timing jitter [1 Hz - 100 kHz] [2]. With DDS-based electronics, low-noise and agile microwave frequency synthesizer was also realized [3]. This new class of photonic signal generator will be suitable for master oscillators in various accelerator-based light sources. [1] D. Kim et al., Opt. Lett. 44, 1068 (2019) [2] D. Kwon et al., Opt. Lett. 42, 5186 (2017) [3] J. Wei et al., Photon. Res. 6, 12 (2018)
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-FEL2019-WEP030
About •	paper received ※ 05 September 2019 paper accepted ※ 22 October 2019 issue date ※ 05 November 2019
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WEP041	Feasibility of Single-Shot Microbunching Diagnostics for a Pre-Bunched Beam at 266 nm	electron, laser, bunching, diagnostics	408
	A.H. Lumpkin AAI/ANL, Lemont, Illinois, USA D.W. Rule Private Address, Silver Spring, USA
	Funding: Work supported by U.S. Department of Energy, Office of Science, under Contract No. DE-AC02-06CH11357. Co-propagating a relativistic electron beam and a high-power laser pulse through a short undulator (modulator) provides an energy modulation which can be converted to a periodic longitudinal density modulation (or microbunching) via the R56 term of a chicane. Such pre-bunching of a beam at the resonant wavelength and the harmonics of a subsequent free-electron laser (FEL) amplifier seeds the process and results in improved gain. We describe potential characterizations of the resulting microbunched electron beams using coherent optical transition radiation (COTR) imaging techniques for transverse size (50 micron), divergence (sub-mrad), trajectory angle (0.1 mrad), spectrum (few nm), and pulse length (sub-ps). The transverse spatial alignment is provided with near-field imaging and the angular alignment is done with far-field imaging and two-foil COTR interferometry (COTRI). Analytical model results for a 266-nm wavelength COTRI case with a 10% microbunching fraction will be presented. COTR gains of 7 million were calculated for an initial charge of 300 pC which enables splitting the optical signal for single-shot measurements of all the cited parameters.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-FEL2019-WEP041
About •	paper received ※ 20 August 2019 paper accepted ※ 29 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	electron, bunching, undulator, 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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WEP070	Influence of Radiation Exposure on the FEL Performance at FLASH	undulator, FEL, 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	undulator, 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	FEL, undulator, electron, detector	495
	S. Grunewald, E. Muller, E. Schneidmiller, K.I. Tiedtke, M.V. Yurkov DESY, Hamburg, Germany O.I. Brovko, A.Yu. Grebentsov, E. Syresin JINR, Dubna, Moscow Region, Russia
	In this report we describe MCP-based radiation detector at FLASH2. Micro-channel plate (MCP) detects scattered radiation from a target (mesh). Use of different targets and geometrical positioning of the MCP plates provides control of photon flux on the detector. MCP detector covers the whole wavelength range of FLASH2 (from 2.x nm to 100 nm). Dynamic range spans from sub-nJ to mJ level (from spontaneous to saturation level). Relative accuracy of single-shot radiation pulse energy measurements in the exponential gain regime is about 1%. DAQ based software is under development which allows to perform cross-correlation of the SASE FEL performance with electron beam jitters. As a result, it is possible: (i) to organize efficient feedback for cancellation of machine jitters, and (ii) to use statistical techniques for characterization of SASE FEL radiation deriving such important quantities as gain curve (gain of the radiation pulse energy and its fluctuations along the undulator), radiation pulse duration, coherence time, and degree of transverse coherence. Relevant experimental results are presented in the paper.
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	undulator, FEL, polarization, 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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WEP080	ROSA: Reconstruction of Spectrogram Autocorrelation for Self-Amplified Spontaneous Emission Free-Electron Lasers	FEL, electron, laser, free-electron-laser	506
	S. Serkez, G. Geloni, N. Gerasimova EuXFEL, Schenefeld, Germany O. Gorobtsov Cornell University, Ithaca, New York, USA B. Sobko LNU, Lviv, Ukraine
	X-ray Free Electron Lasers (FELs) have opened new avenues in photon science, providing coherent X-ray radiation pulses orders of magnitude brighter and shorter than previously possible. The emerging concept of "beam by design" in FEL accelerator physics aims for accurate manipulation of the electron beam to tailor spectral and temporal properties of radiation for specific experimental purposes, such as X-ray pump/X-ray probe and multiple wavelength experiments. A cost-efficient method to extract information on longitudinal Wigner distribution function of emitted FEL pulses is proposed. It requires only an ensemble of measured FEL spectra.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-FEL2019-WEP080
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	undulator, electron, 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, undulator, electron, 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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WEP093	Radiation Damage Monitoring at PAL-XFEL	undulator, 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	undulator, FEL, electron, 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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WEP101	Linear Polarisation via a Delta Afterburner for the CompactLight Facility	undulator, FEL, polarization, 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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WEP104	A High-Power, High-Repetition Rate THz Source for LCLS-II Pump-Probe Experiments	wiggler, FEL, laser, injection	556
	Z. Zhang, A.S. Fisher, M.C. Hoffmann, Z. Huang, B.T. Jacobson, P.S. Kirchmann, W.S. Lee, A. Lindenberg, E.A. Nanni, R.W. Schoenlein SLAC, Menlo Park, California, USA S. Sasaki, J.Z. Xu ANL, Lemont, Illinois, USA
	Experiments using a THz pump and an x-ray probe at an x-ray free-electron laser (XFEL) facility like LCLS-II require frequency-tunable (3 to 20 THz), narrow bandwidth ( ∼ 10\%), carrier-envelope-phase-stable THz pulses that produce high fields (>1MV/cm) at the repetition rate of the x rays and well synchronized with them. In this paper, we study a two-bunch scheme to generate THz radiation at LCLS-II: the first bunch produces THz radiation in a permanent-magnet or electromagnet wiggler immediately following the LCLS-II undulator that produces X-rays from the second bunch. The initial time delay between the two bunches is optimized to compensate for the path difference in transport. We describe the two-bunch beam dynamics, the THz wiggler and radiation, as well as the transport system bringing the THz pulses from the wiggler to the experimental hall.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-FEL2019-WEP104
About •	paper received ※ 23 August 2019 paper accepted ※ 17 September 2019 issue date ※ 05 November 2019
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WEP107	Polarizing Afterburner for the LCLS-II Undulator Line	undulator, 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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WED02	Absorbed Radiation Doses on the European XFEL Undulator Systems During Early User Experiments	undulator, operation, FEL, photon	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]
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-FEL2019-WED02
About •	paper received ※ 19 August 2019 paper accepted ※ 27 August 2019 issue date ※ 05 November 2019
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THA04	Ultrafast Magnetisation Dynamics at the Low-Fluence Limit Supported by External Magnetic Fields	laser, scattering, FEL, electron	574
	M. Riepp, K. Bagschik, T. Golz, G. Grübel, L. Müller, A. Philippi-Kobs, W.R. Roseker, R. Rysov, N. Stojanovic, M. Walther DESY, Hamburg, Germany F. Capotondi, M. Kiskinova, D. Naumenko, E. Pedersoli Elettra-Sincrotrone Trieste S.C.p.A., Basovizza, Italy R. Frömter, H.P. Oepen University of Hamburg, Institut für Experimentalphysik, Hamburg, Germany
	We report on ultrafast magnetisation dynamics in ferro-magnetic cobalt/platinum multilayers upon pumping by near and mid to far infrared radiation, utilizing sub-100 femtosecond free-electron laser pulses. The evolution of the excited magnetic state is studied on femtosecond timescales with nanometre spatial resolution and element selectivity, employing time-resolved magnetic small-angle X-ray scattering. The obtained results contribute to the ongoing discussion to what extent either coupling of the electromagnetic field or rather quasi-instantaneous heating of the electron-system is the driving force for phenomena like ultrafast demagnetization or all-optical helicity-dependent switching.
	Slides THA04 [4.980 MB]
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-FEL2019-THA04
About •	paper received ※ 19 August 2019 paper accepted ※ 19 September 2019 issue date ※ 05 November 2019
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THB02	Understanding 1D to 3D Coherent Synchrotron Radiation Effects	simulation, emittance, electron, experiment	578
	A.D. Brynes STFC/DL/ASTeC, Daresbury, Warrington, Cheshire, United Kingdom
	Collective effects such as coherent synchrotron radiation (CSR) can have a strong influence of the properties of an electron bunch with respect to the quality of the FEL light that it produces. In particular, CSR experienced by a bunch on a curved trajectory can increase the transverse emittance of a beam. In this contribution, we present an extension to the well-established 1D theory of CSR by accounting fully for the forces experienced in the entrance and exit transients of a bending magnet. A new module of the General Particle Tracer (GPT) tracking code was developed for this study, showing good agreement with theory. In addition to this analysis, we present experimental measurements of the emittance growth experienced in the FERMI bunch compressor chicane as a function of bunch length. When the bunch undergoes extreme compression, the 1D theory breaks down and is no longer valid. A comparison between the 1D theory, experimental measurements and a number of codes which simulate CSR differently are presented, showing better agreement when the transverse properties of the bunch are taken into account.
	Slides THB02 [3.591 MB]
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-FEL2019-THB02
About •	paper received ※ 19 August 2019 paper accepted ※ 27 August 2019 issue date ※ 05 November 2019
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THP009	Space Charge Field Beam Dynamics Simulations for the THz SASE FEL at PITZ	undulator, 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
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-FEL2019-THP009
About •	paper received ※ 20 August 2019 paper accepted ※ 27 August 2019 issue date ※ 05 November 2019
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THP012	Compact FEL-Driven Inverse Compton Scattering Gamma-Ray Source	photon, electron, FEL, undulator	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.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-FEL2019-THP012
About •	paper received ※ 19 August 2019 paper accepted ※ 25 August 2019 issue date ※ 05 November 2019
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THP013	User Operation of Sub-Picosecond THz Coherent Transition Radiation Parasitic to a VUV FEL	electron, linac, target, FEL	621
	S. Di Mitri, N. Adhlakha, E. Allaria, L. Badano, G. De Ninno, P. Di Pietro, G. Gaio, L. Giannessi, G. Penco, A. Perucchi, P. Rebernik Ribič, E. Roussel, S. Spampinati, C. Spezzani, M. Trovò, M. Veronese Elettra-Sincrotrone Trieste S.C.p.A., Basovizza, Italy G. De Ninno University of Nova Gorica, Nova Gorica, Slovenia L. Giannessi ENEA C.R. Frascati, Frascati (Roma), Italy S. Lupi Coherentia, Naples, Italy S. Lupi Sapienza University of Rome, Roma, Italy F. Piccirilli IOM-CNR, Trieste, Italy E. Roussel PhLAM/CERLA, Villeneuve d’Ascq, France E. Roussel PhLAM/CERCLA, Villeneuve d’Ascq Cedex, France
	Coherent transition radiation is enhanced in intensity and extended in frequency spectral range by the electron beam manipulation in the beam dump beam line of the FERMI FEL, by exploiting the interplay of coherent synchrotron radiation instability and electron beam optics [1]. Experimental observations at the TeraFERMI beamline [2] confirm intensity peaks at around 1 THz and extending up to 8.5 THz, for up to 80 µJ pulse energy integrated over the full bandwidth. By virtue of its implementation in an FEL beam dump line, this work might stimulate the development of user-oriented multi-THz beamlines parasitic and self-synchronized to VUV and X-ray FELs. [1] S. Di Mitri et al., Scientific Reports, 8, 11661 (2018). [2] A. Perucchi et al., Synch. Rad. News 4, 30 (2017).
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-FEL2019-THP013
About •	paper received ※ 29 July 2019 paper accepted ※ 27 August 2019 issue date ※ 05 November 2019
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THP022	A General Optimization Method for High Harmonic Generation Beamline	laser, electron, free-electron-laser, coupling	638
	Y. Zhang, X.J. Deng, W.-H. Huang, Z. Pan, C.-X. Tang TUB, Beijing, People’s Republic of China
	Shorter bunches produce a more coherent radiation and contain higher harmonic components. Here, based on transverse and longitudinal phase space coupling, a general method for analyzing the production of very short beam and searching for compression beamline is presented. With this method, several beamlines are found and optimized. The electron beam can be compressed to tens of nanometers, generating coherent high harmonic radiation.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-FEL2019-THP022
About •	paper received ※ 20 August 2019 paper accepted ※ 29 August 2019 issue date ※ 05 November 2019
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THP024	Spontaneous Coherent Radiation of Stabilized Dense Electron Bunches	electron, undulator, 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
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-FEL2019-THP024
About •	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	undulator, laser, FEL, linac	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.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-FEL2019-THP030
About •	paper received ※ 20 August 2019 paper accepted ※ 29 August 2019 issue date ※ 05 November 2019
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THP031	Simulation and Optimization of Injector System for the Pre-bunched THz FEL	electron, linac, gun, simulation	654
	N. Chaisueb, S. Rimjaem Chiang Mai University, Chiang Mai, Thailand S. Rimjaem ThEP Center, Commission on Higher Education, Bangkok, Thailand
	A linac-based light source for generation of infrared free-electron laser is under the development at Chiang Mai University, Thailand. The injector system of the facility consists mainly of an S-band thermionic cathode RF electron gun, a pre-bunch compressor in a form of an alpha magnet and a travelling-wave linac structure. Two 180-degree magnetic bunch compressors are installed downstream the injector system. Two separate radiation beamlines for mid-infrared (MIR) and terahertz (THz) free-electron laser (FEL) are located following the bunch compressor systems. In this contribution, we focus only on the coherent and high-power pre-bunch THz FEL that is generated from electron bunches with a femtosecond length. Electron beam dynamic simulations with program ASTRA were performed to obtain optimal electron beam properties. Optimization of the injector system for the THz FEL is thus presented. The simulated results show that the beam at the linac exit has a bunch length of 282 fs with a charge of 200 pC when the linac RF phase is 90° and the alpha gradient is 300 G/cm. This optimal condition will be used as an input for simulation in the 180-degree bunch compressor system and in the THz undulator magnet.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-FEL2019-THP031
About •	paper received ※ 20 August 2019 paper accepted ※ 28 August 2019 issue date ※ 05 November 2019
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THP037	A Novel One-Dimensional Model for CSR Wakefields	wakefield, synchrotron, synchrotron-radiation, electron	669
	G. Stupakov SLAC, Menlo Park, California, USA
	The existing 1D models of the coherent synchrotron radiation (CSR) wakefield in free space assume that the longitudinal bunch distribution remains constant when the beam propagates through a magnetic lattice. In this paper, we derive a formula for a 1D CSR wake that takes into account variation of the bunch length along the orbit. The formula is valid for arbitrary curvilinear beam trajectory. We analyze the validity of the 1D model in a typical implementation of an FEL bunch compressor.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-FEL2019-THP037
About •	paper received ※ 12 August 2019 paper accepted ※ 26 August 2019 issue date ※ 05 November 2019
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THP049	A Versatile THz Source for High-Repetition Rate XFELs	FEL, GUI, undulator, electron	688
	F. Lemery, M. Dohlus, K. Flöttmann, M. Marx DESY, Hamburg, Germany M. Ivanyan, V.M. Tsakanov CANDLE, Yerevan, Armenia
	Funding: FL was partially funded by the European Union¿s Horizon 2020 Research and Innovation programme under Grant Agreement No. 730871 The development of high-repetition rate XFELs brings an exciting time for novel fundamental science exploration via pump-probe interactions. Laser-based pump sources can provide a wide range of wavelengths (200-10000~nm) via various gain media. These sources can also be extended with optical parametric amplifiers to cover a largely versatile spectral and bandwidth range. However beyond 10~μm, toward the THz regime, there exists no suitable gain media, and optical-to-THz efficiencies are limited below 1\%. In this paper we discuss the use of Cherenkov-based radiators with conventional electron bunches to generate high-power THz radiation over a wide range of parameters for existing and future XFEL facilities.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-FEL2019-THP049
About •	paper received ※ 25 August 2019 paper accepted ※ 28 August 2019 issue date ※ 05 November 2019
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THP051	Generating Trains of Attosecond Pulses with a Free-Electron Laser	FEL, electron, laser, free-electron-laser	692
	S. Serkez, G. Geloni EuXFEL, Schenefeld, Germany M.H. Cho, H.-S. Kang, G. Kim, J.H. Ko, C.-K. Min, I.H. Nam, C.H. Shim PAL, Pohang, Republic of Korea F.-J. Decker SLAC, Menlo Park, California, USA J.H. Ko, C.H. Shim POSTECH, Pohang, Kyungbuk, Republic of Korea Yu. Shvyd’ko ANL, Lemont, Illinois, USA
	Recently, a Hard X-ray Self-Seeding setup was commissioned at PAL XFEL. Its main purpose is to increase the temporal coherence of FEL radiation in an active way. We report another application of this setup to generate trains of short sub-femtosecond pulses with linked phases. We discuss preliminary results of both experiment and corresponding simulations as well as indirect diagnostics of the radiation properties.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-FEL2019-THP051
About •	paper received ※ 20 August 2019 paper accepted ※ 27 August 2019 issue date ※ 05 November 2019
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THP055	A Storage Ring Design for Steady-State Microbunching to Generate Coherent EUV Light Source	lattice, storage-ring, electron, simulation	700
	Z. Pan, X.J. Deng, W.-H. Huang, T. Rui, C.-X. Tang, Y. Zhang TUB, Beijing, People’s Republic of China A. Chao SLAC, Menlo Park, California, USA W. Wan ShanghaiTech University, Shanghai, People’s Republic of China
	The proposal of Steady State Microbunching (SSMB) makes it available to generate high average power coherent radiation, especially has the potential to generate kW level of EUV source for lithography. In order to achieve and maintain SSMB, we propose several concepts. One is that a very short electron bunch below 100 nm is stored in the ring, inserting a strong focusing part to compress the bunch to ~3 nm, then radiating coherently, which is called longitudinal strong focusing (LSF) scheme. We have optimized the candidate lattice to achieve the very short electron bunch storage and microbunching for electron beam. The tracking results show the equilibrium length of the electron bunch is about 400 nm and no particles lose after 4.3 damping time while only single-particle effect is considered. More optimization and some new design based on the simulation results are still implementing.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-FEL2019-THP055
About •	paper received ※ 19 August 2019 paper accepted ※ 26 August 2019 issue date ※ 05 November 2019
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THP060	Development of RF-Undulators and Powering Sources for Compact Efficient Compton FEL-Scattrons	undulator, electron, 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.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-FEL2019-THP060
About •	paper received ※ 15 August 2019 paper accepted ※ 25 August 2019 issue date ※ 05 November 2019
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THP081	PolFEL — New Facility in Poland	FEL, electron, photon, experiment	746
	K. Szamota-Leandersson, P.J. Czuma, P. Krawczyk, J. Krzywiński, R. Nietubyć, M. Staszczak, J. Szewiński NCBJ, Świerk/Otwock, Poland W. Bal, J. Poznański IBB, Warsaw, Poland A. Bartnik, H. Fiedorowicz, K. Janulewicz, N. Palka MUT, Warsaw, Poland J.K. Sekutowicz DESY, Hamburg, Germany
	Funding: European Regional Development Fund ¿ Smart Growth In 2018 funds for the free electron laser PolFEL project was received. PolFEL will be driven by cw operating superconducting linac with SRF electron source. PolFEL will generate THz, IR and VIS-VUV radiation in two beamlines, respectively. In the first one, with electron beam below 80 MeV, the THz/IR radiation source will be generated in permanent magnet supper-radiant undulator, delivering THz radiation in 0.5 to 6 THz range. In the second beam line with up to 180 MeV electrons, the VIS/VUV radiation will be generated in the SASE undulator delivering coherent radiation down to 55 nm wavelength in the third harmonic, with sub-100 fs pulse duration. At the moment, four end-stations are planned. Experiments will be equipped with dedicated Pump-Probe spectrometer system as well. In the project, also, the Inverse Compton Scattering experiment is planned. In this contribution we will describe PolFEL facility in more details.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-FEL2019-THP081
About •	paper received ※ 29 August 2019 paper accepted ※ 18 September 2019 issue date ※ 05 November 2019
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Paper

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MOA01

Riding the FEL Instability (Dedicated to Alberto Renieri)

electron, laser, storage-ring, free-electron-laser

1

G. Dattoli
ENEA C.R. Frascati, Frascati (Roma), Italy
M.-E. Couprie
SOLEIL, Gif-sur-Yvette, France
C. Pellegrini
SLAC, Menlo Park, California, USA

The Free Electron Laser (FEL) operation, like that of any Free Electron source of coherent radiation, is associated with the onset of an instability. The interplay between the FEL and other instabilities, affecting the beam, is one of the interesting aspects of the associated dynamics. It involves issues of practical interest (Renieri Limit in Storage Ring FELs, suppression of instabilities like saw-tooth and synchrotron…). The paper reviews these problems and offers an overview of the scientific contribution of Alberto Renieri to the FEL from this perspective.

Slides MOA01 [5.143 MB]

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paper received ※ 26 August 2019 paper accepted ※ 09 September 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

FEL, undulator, electron, experiment

38

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

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

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paper received ※ 20 August 2019 paper accepted ※ 28 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, dipole, experiment, undulator

45

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

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

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TUP004

A Superradiant THz Undulator Source for XFELs

undulator, FEL, electron, 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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TUP007

Experience with the Superradiant THz User Facility Driven by a Quasi-CW SRF Accelerator at ELBE

detector, electron, SRF, experiment

56

M. Bawatna, B.W. Green
HZDR, Dresden, Germany

Instabilities in beam and bunch parameters, such as bunch charge, beam energy or changes in the phase or amplitude of the accelerating field in the RF cavities can be the source of noise in the various secondary sources driven by the electron beam. Bunch charge fluctuations lead to intensity instabilities in the super-radiant THz sources. The primary electron beam driving the light sources has a maximum energy of 40 MeV and a maximum current of 1.6 mA. Depending on the mode of operation required, there are two available injectors in use at ELBE. The first is the thermionic injector, which is used for regular operating modes and supports repetition rates up to 13 MHz and bunch charges up to 100 pC. The second is the SRF photo-cathode injector, which is used for experiments that may require lower emittance or higher bunch charges of up to 1 nC. It has a maximum repetition rate of 13 MHz, which can be adjusted to lower rates if desired, also including different macro pulse modes of operation. In this contribution, we will present our work in the pulse-resolved intensity measurement that allows for correction of intensity instabilities.

Poster TUP007 [0.658 MB]

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TUP008

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

undulator, electron, 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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paper received ※ 29 August 2019 paper accepted ※ 29 August 2019 issue date ※ 05 November 2019

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TUP009

Integration of an XFELO at the European XFEL Facility

FEL, electron, simulation, cavity

62

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

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

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TUP012

Smith-Purcell Radiation Emitted by Pico-second Electron Bunches from a 30 keV Photo-Electron Gun

electron, experiment, laser, gun

66

M.R. Asakawa, S. Yamaguchi
Kansai University, Osaka, Japan

In this paper, an experiment to generate Smith-Purcell radiation using pico-second electron bunches is reported. The electron bunch was produced by a DC 30 keV photo-electron electron gun driven by a 100 fs Ti:sapphire laser. The charge of the bunch varied from 1 pC to 300 pC by changing the laser power. Smith-Purcell radiation experiment was performed with the central part of the entire electron bunch. Estimation of pulsewidth of the bunch based on the envelope equation showed that the pulsewidth of the bunch at the anode electrode increased from 0.8 ps to 3.2 ps as the bunch charge increase from 0.1 pC to 11 pC. Such electron bunch was traveled along the surface of the metallic grating with a period of 2 mm. The radiation wavelength was estimated to be 4 mm at an obserbation angle of 10 degree. The radiation power was measured by a bolometer and quadraticallly increased with the bunch charge. Numerical simulation of this experiment indicated the enhancement of the harmonic components of the radiation. We are now constructing a THz-TDS system to measure the time-trace of the electric field of the radiation.

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TUP014

Crossed-Undulator Configuration for Variable Polarized THz Source

undulator, 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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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

electron, FEL, undulator, laser

73

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

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

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

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TUP017

Terahertz FEL Simulation in PAL XFEL

FEL, electron, simulation, undulator

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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TUP018

Superradiant Emission of Electron Bunches Based on Cherenkov Excitation of Surface Waves in 1D and 2D Periodical Lattices: Theory and Experiments

electron, GUI, experiment, simulation

80

A. Malkin, N.S. Ginzburg, A. Sergeev, I.V. Zheleznov, I.V. Zotova
IAP/RAS, Nizhny Novgorod, Russia
M.I. Yalandin
RAS/IEP, Ekaterinburg, Russia
V.Yu. Zaslavsky
UNN, Nizhny Novgorod, Russia

Funding: The work was supported by RFBR grant no. 17-08-01072
In recent years, significant progress was achieved in generation of high-power ultrashort microwave pulses based on superradiance (SR) of electron bunches extended in the wavelength scale. In this process, coherent emission from the entire volume of the bunch occurs due to the development of microbunching and slippage of the wave with respect to electrons. An obvious method for generation of high-power sub-THz radiation is the implementation of oversized periodical slow-wave structures where evanescent surface waves can be excited. We report of the experiments on Cherenkov generation of 150 ps SR pulses with a central frequency of 0.14 THz, and an extremely high peak power up to 70 MW. In order to generate spatially coherent radiation in shorter wavelength ranges (including THz band) in strongly oversized waveguiding systems, we propose a slow wave structure with double periodic corrugation (2D SWS). Using the quasi-optical theory and PIC simulations, we demonstrate the applicability of such 2D SWS and its advantages against traditional 1D SWS. Proof of principle experiments on observation G-band Cherenkov SR in 2D SWS are currently in progress.

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

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TUP021

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

electron, FEL, simulation, feedback

91

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

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

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reference for this paper ※ https://doi.org/10.18429/JACoW-FEL2019-TUP021

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

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TUP023

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

FEL, simulation, undulator, bunching

94

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

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

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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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TUP024

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

FEL, electron, experiment, controls

98

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

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

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

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TUP032

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

FEL, cavity, electron, undulator

118

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

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

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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, electron, undulator

127

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

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

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

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

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TUP037

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

electron, storage-ring, emittance, undulator

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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TUP038

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

FEL, electron, experiment, laser

134

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

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

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

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TUP041

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

undulator, simulation, electron, 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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paper received ※ 01 August 2019 paper accepted ※ 27 August 2019 issue date ※ 05 November 2019

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TUP042

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

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

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TUP051

Plasma Accelerator Driven Coherent Spontaneous Emission

electron, FEL, bunching, undulator

157

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

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

Poster TUP051 [1.401 MB]

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

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TUP053

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

photon, FEL, experiment, cavity

161

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

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

Poster TUP053 [0.929 MB]

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

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TUP054

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

electron, photon, FEL, laser

165

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

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

Poster TUP054 [0.386 MB]

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

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TUP057

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

undulator, FEL, electron, 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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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, photon, electron, undulator

180

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

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

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

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

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TUP059

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

FEL, undulator, 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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TUP062

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

FEL, electron, photon, experiment

195

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

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

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

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

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TUP065

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

undulator, electron, synchrotron, FEL

206

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

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

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

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

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TUP072

Orbital Angular Momentum from SASE

electron, quadrupole, FEL, undulator

218

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

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

Poster TUP072 [1.311 MB]

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

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

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TUP073

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

FEL, laser, electron, cavity

222

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

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

Poster TUP073 [0.521 MB]

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

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

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TUP079

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

FEL, undulator, electron, simulation

242

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

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

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

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

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TUP080

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

laser, electron, undulator, 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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reference for this paper ※ https://doi.org/10.18429/JACoW-FEL2019-TUP080

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

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TUP088

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

electron, laser, FEL, free-electron-laser

258

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

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

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

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

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TUP092

XFEL Third Harmonic Statistics Measurement at LCLS

FEL, photon, undulator, experiment

269

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

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

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

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

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TUD03

Fine and Hyperfine Structure of FEL Emission Spectra

FEL, electron, laser, experiment

276

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

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

Slides TUD03 [3.177 MB]

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

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

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TUT01

Superradiance and Stimulated-Superradiant Emission of Bunched Electron Beams

electron, wiggler, FEL, undulator

288

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

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

Slides TUT01 [11.391 MB]

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reference for this paper ※ https://doi.org/10.18429/JACoW-FEL2019-TUT01

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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, FEL, electron, undulator

350

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

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

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reference for this paper ※ https://doi.org/10.18429/JACoW-FEL2019-WEP012

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

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WEP030

All-Fiber Photonic, Ultralow-Noise, Robust Optical and Microwave Signal Generators for FELs and UED

laser, timing, photon, operation

382

J. Kim, I.J. Jeon, D. Kim, D. Kwon
KAIST, Daejeon, Republic of Korea

Funding: National Research Foundation of Korea (2018R1A2B3001793) and Korea Atomic Energy Research Institute
Optical timing and synchronization is becoming a more important and essential element for ultrafast X-ray and electron science. As a result, compact, ultralow-noise, mechanically robust and long-term stable optical and microwave signal generators are highly desirable for future XFELs and UEDs. Here we show that the combination of mode-locked fiber laser and fiber delay-based stabilization method enables the generation of ultralow-noise optical and microwave signals. We show that all-PM fiber lasers can provide excellent mechanical robustness: stable laser operation over >1 hour is maintained even in continuous 1.5 g vibrations [1]. Using a compactly packaged fiber delay as the timing reference, we could stabilize the repetition-rate phase noise of mode-locked lasers down to -100 dBc/Hz and -160 dBc/Hz at 1 Hz and 10 kHz offset frequency, respectively, at 1 GHz carrier, which corresponds to only 1.4 fs rms absolute timing jitter [1 Hz - 100 kHz] [2]. With DDS-based electronics, low-noise and agile microwave frequency synthesizer was also realized [3]. This new class of photonic signal generator will be suitable for master oscillators in various accelerator-based light sources.
[1] D. Kim et al., Opt. Lett. 44, 1068 (2019)
[2] D. Kwon et al., Opt. Lett. 42, 5186 (2017)
[3] J. Wei et al., Photon. Res. 6, 12 (2018)

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reference for this paper ※ https://doi.org/10.18429/JACoW-FEL2019-WEP030

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paper received ※ 05 September 2019 paper accepted ※ 22 October 2019 issue date ※ 05 November 2019

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WEP041

Feasibility of Single-Shot Microbunching Diagnostics for a Pre-Bunched Beam at 266 nm

electron, laser, bunching, diagnostics

408

A.H. Lumpkin
AAI/ANL, Lemont, Illinois, USA
D.W. Rule
Private Address, Silver Spring, USA

Funding: Work supported by U.S. Department of Energy, Office of Science, under Contract No. DE-AC02-06CH11357.
Co-propagating a relativistic electron beam and a high-power laser pulse through a short undulator (modulator) provides an energy modulation which can be converted to a periodic longitudinal density modulation (or microbunching) via the R56 term of a chicane. Such pre-bunching of a beam at the resonant wavelength and the harmonics of a subsequent free-electron laser (FEL) amplifier seeds the process and results in improved gain. We describe potential characterizations of the resulting microbunched electron beams using coherent optical transition radiation (COTR) imaging techniques for transverse size (50 micron), divergence (sub-mrad), trajectory angle (0.1 mrad), spectrum (few nm), and pulse length (sub-ps). The transverse spatial alignment is provided with near-field imaging and the angular alignment is done with far-field imaging and two-foil COTR interferometry (COTRI). Analytical model results for a 266-nm wavelength COTRI case with a 10% microbunching fraction will be presented. COTR gains of 7 million were calculated for an initial charge of 300 pC which enables splitting the optical signal for single-shot measurements of all the cited parameters.

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reference for this paper ※ https://doi.org/10.18429/JACoW-FEL2019-WEP041

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paper received ※ 20 August 2019 paper accepted ※ 29 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

electron, bunching, undulator, 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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WEP070

Influence of Radiation Exposure on the FEL Performance at FLASH

undulator, FEL, 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

undulator, 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

FEL, undulator, electron, detector

495

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

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

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

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

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WEP076

A Superconducting Undulator With Variable Polarization Direction for the European FEL

undulator, FEL, polarization, 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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WEP080

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

FEL, electron, laser, free-electron-laser

506

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

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

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

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

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WEP086

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

undulator, electron, 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, undulator, electron, 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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WEP093

Radiation Damage Monitoring at PAL-XFEL

undulator, 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

undulator, FEL, electron, 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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WEP101

Linear Polarisation via a Delta Afterburner for the CompactLight Facility

undulator, FEL, polarization, bunching

549

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

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

Poster WEP101 [1.083 MB]

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

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WEP104

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

wiggler, FEL, laser, injection

556

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

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

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

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

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WEP107

Polarizing Afterburner for the LCLS-II Undulator Line

undulator, 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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WED02

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

undulator, operation, FEL, photon

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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THA04

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

laser, scattering, FEL, electron

574

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

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

Slides THA04 [4.980 MB]

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

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THB02

Understanding 1D to 3D Coherent Synchrotron Radiation Effects

simulation, emittance, electron, experiment

578

A.D. Brynes
STFC/DL/ASTeC, Daresbury, Warrington, Cheshire, United Kingdom

Collective effects such as coherent synchrotron radiation (CSR) can have a strong influence of the properties of an electron bunch with respect to the quality of the FEL light that it produces. In particular, CSR experienced by a bunch on a curved trajectory can increase the transverse emittance of a beam. In this contribution, we present an extension to the well-established 1D theory of CSR by accounting fully for the forces experienced in the entrance and exit transients of a bending magnet. A new module of the General Particle Tracer (GPT) tracking code was developed for this study, showing good agreement with theory. In addition to this analysis, we present experimental measurements of the emittance growth experienced in the FERMI bunch compressor chicane as a function of bunch length. When the bunch undergoes extreme compression, the 1D theory breaks down and is no longer valid. A comparison between the 1D theory, experimental measurements and a number of codes which simulate CSR differently are presented, showing better agreement when the transverse properties of the bunch are taken into account.

Slides THB02 [3.591 MB]

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reference for this paper ※ https://doi.org/10.18429/JACoW-FEL2019-THB02

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

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THP009

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

undulator, 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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reference for this paper ※ https://doi.org/10.18429/JACoW-FEL2019-THP009

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

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THP012

Compact FEL-Driven Inverse Compton Scattering Gamma-Ray Source

photon, electron, FEL, undulator

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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reference for this paper ※ https://doi.org/10.18429/JACoW-FEL2019-THP012

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

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THP013

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

electron, linac, target, FEL

621

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

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

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

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

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THP022

A General Optimization Method for High Harmonic Generation Beamline

laser, electron, free-electron-laser, coupling

638

Y. Zhang, X.J. Deng, W.-H. Huang, Z. Pan, C.-X. Tang
TUB, Beijing, People’s Republic of China

Shorter bunches produce a more coherent radiation and contain higher harmonic components. Here, based on transverse and longitudinal phase space coupling, a general method for analyzing the production of very short beam and searching for compression beamline is presented. With this method, several beamlines are found and optimized. The electron beam can be compressed to tens of nanometers, generating coherent high harmonic radiation.

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reference for this paper ※ https://doi.org/10.18429/JACoW-FEL2019-THP022

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

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THP024

Spontaneous Coherent Radiation of Stabilized Dense Electron Bunches

electron, undulator, 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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reference for this paper ※ https://doi.org/10.18429/JACoW-FEL2019-THP024

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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

undulator, laser, FEL, linac

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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THP031

Simulation and Optimization of Injector System for the Pre-bunched THz FEL

electron, linac, gun, simulation

654

N. Chaisueb, S. Rimjaem
Chiang Mai University, Chiang Mai, Thailand
S. Rimjaem
ThEP Center, Commission on Higher Education, Bangkok, Thailand

A linac-based light source for generation of infrared free-electron laser is under the development at Chiang Mai University, Thailand. The injector system of the facility consists mainly of an S-band thermionic cathode RF electron gun, a pre-bunch compressor in a form of an alpha magnet and a travelling-wave linac structure. Two 180-degree magnetic bunch compressors are installed downstream the injector system. Two separate radiation beamlines for mid-infrared (MIR) and terahertz (THz) free-electron laser (FEL) are located following the bunch compressor systems. In this contribution, we focus only on the coherent and high-power pre-bunch THz FEL that is generated from electron bunches with a femtosecond length. Electron beam dynamic simulations with program ASTRA were performed to obtain optimal electron beam properties. Optimization of the injector system for the THz FEL is thus presented. The simulated results show that the beam at the linac exit has a bunch length of 282 fs with a charge of 200 pC when the linac RF phase is 90° and the alpha gradient is 300 G/cm. This optimal condition will be used as an input for simulation in the 180-degree bunch compressor system and in the THz undulator magnet.

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reference for this paper ※ https://doi.org/10.18429/JACoW-FEL2019-THP031

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

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THP037

A Novel One-Dimensional Model for CSR Wakefields

wakefield, synchrotron, synchrotron-radiation, electron

669

G. Stupakov
SLAC, Menlo Park, California, USA

The existing 1D models of the coherent synchrotron radiation (CSR) wakefield in free space assume that the longitudinal bunch distribution remains constant when the beam propagates through a magnetic lattice. In this paper, we derive a formula for a 1D CSR wake that takes into account variation of the bunch length along the orbit. The formula is valid for arbitrary curvilinear beam trajectory. We analyze the validity of the 1D model in a typical implementation of an FEL bunch compressor.

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paper received ※ 12 August 2019 paper accepted ※ 26 August 2019 issue date ※ 05 November 2019

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THP049

A Versatile THz Source for High-Repetition Rate XFELs

FEL, GUI, undulator, electron

688

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

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

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

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THP051

Generating Trains of Attosecond Pulses with a Free-Electron Laser

FEL, electron, laser, free-electron-laser

692

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

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

DOI •

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

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

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THP055

A Storage Ring Design for Steady-State Microbunching to Generate Coherent EUV Light Source

lattice, storage-ring, electron, simulation

700

Z. Pan, X.J. Deng, W.-H. Huang, T. Rui, C.-X. Tang, Y. Zhang
TUB, Beijing, People’s Republic of China
A. Chao
SLAC, Menlo Park, California, USA
W. Wan
ShanghaiTech University, Shanghai, People’s Republic of China

The proposal of Steady State Microbunching (SSMB) makes it available to generate high average power coherent radiation, especially has the potential to generate kW level of EUV source for lithography. In order to achieve and maintain SSMB, we propose several concepts. One is that a very short electron bunch below 100 nm is stored in the ring, inserting a strong focusing part to compress the bunch to ~3 nm, then radiating coherently, which is called longitudinal strong focusing (LSF) scheme. We have optimized the candidate lattice to achieve the very short electron bunch storage and microbunching for electron beam. The tracking results show the equilibrium length of the electron bunch is about 400 nm and no particles lose after 4.3 damping time while only single-particle effect is considered. More optimization and some new design based on the simulation results are still implementing.

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reference for this paper ※ https://doi.org/10.18429/JACoW-FEL2019-THP055

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

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THP060

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

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

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

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THP081

PolFEL — New Facility in Poland

FEL, electron, photon, experiment

746

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

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

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

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

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