Keyword: radiation
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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 icon 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 icon 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 icon 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 icon 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 icon 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 icon 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 icon 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 icon 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 icon 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 icon 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 icon 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 icon 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 icon 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 icon 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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