Electron Beam Dynamics
Paper Title Page
THB01
Using an E-SASE Compression to Suppress Microbunch Instability and Resistive-Wall Wake Effects  
 
  • P.M. Anisimov
    LANL, Los Alamos, New Mexico, USA
 
  Funding: Research presented in this presentation was supported by the Laboratory Directed Research and Development program of Los Alamos National Laboratory under project number 20180535ECR.
High brightness electron sources, such as photo injectors, deliver electron beams with a few Ampere peak currents yet high energy X-ray free-electron lasers require electron beams with >3kA peak currents to operate. In order to bridge this gap, a 100x beam compression that does not reduce the brightness of an electron beam has to take place. We will present our study of an E-SASE based compression scheme aimed at satisfying the requirements of high energy X-ray free electron lasers regarding electron beam currents, energy spreads and emittances. The E-SASE compression is based on a laser modulation of an electron beam energy and subsequent compression in a small magnetic chicane, which results in a train of high current bunches that are synchronized to the external laser and could be used in pump-probe experiments. A unique time profile of an electron beam is expected to suppress the resistive-wall wake effects.
 
slides icon Slides THB01 [11.055 MB]  
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THB02 Understanding 1D to 3D Coherent Synchrotron Radiation Effects 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 When the bunch undergoes extreme compression, the 1D theory breaks down and is no longer valid.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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THB03
Emittance Measurements and Minimization at SwissFEL  
 
  • E. Prat, M. Aiba, S. Bettoni, P. Craievich, P. Dijkstal, E. Ferrari, R. Ischebeck, F. Löhl, A. Malyzhenkov, G.L. Orlandi, S. Reiche, T. Schietinger
    PSI, Villigen PSI, Switzerland
 
  The transverse emittance of the electron beam is a fundamental parameter that determines the performance of free-electron-lasers (FELs). In this contribution, we present emittance measurements carried out at SwissFEL, the X-ray FEL facility that recently started to operate at PSI in Switzerland, including a description of our measurement methods and optimization procedures. We obtained slice emittance values at the undulator entrance down to ~200 nm for an electron beam with a charge of 200 pC and an r.m.s. duration of ~30 fs. Furthermore, we achieved slice emittances as low as ~100 nm for 10 pC beams with few femtosecond duration.  
slides icon Slides THB03 [6.285 MB]  
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THB04 Longitudinal Phase Space Study on Injector Beam of High Repetition Rate X-Ray FEL 584
 
  • Q. Gu
    SSRF, Shanghai, People’s Republic of China
  • Z. Wang
    SARI-CAS, Pudong, Shanghai, People’s Republic of China
 
  The longitudinal phase space of the high repetition rate injector beam usually twisted and deteriorated by the space charge force. It causes the correlated energy spread and the local chirp within the beam, which could not compensated by the harmonic correction. As a consequence of this problem, one could not get ideal beam with a peak current more than kiloamperes. In this paper several approaches have been studied to relieve this effect and get the well compressed beam for the lasing.  
slides icon Slides THB04 [3.151 MB]  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-FEL2019-THB04  
About • paper received ※ 26 August 2019       paper accepted ※ 16 September 2019       issue date ※ 05 November 2019  
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THP001 Steffen Hard-Edge Model for Quadrupoles with Extended Fringe-Fields at the European XFEL 588
 
  • N. Golubeva, V. Balandin, W. Decking, L. Fröhlich, M. Scholz
    DESY, Hamburg, Germany
 
  For modeling of linear focusing properties of quadrupole magnets the conventional rectangular model is commonly used for the design and calculations of the linear beam optics for accelerators. At the European XFEL the quadrupole magnets are described using a more accurate Steffen hard-edge model. In this paper we discuss the application of the Steffen approach for the European XFEL quadrupoles and present the examination of the model with the orbit response matrix technique.  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-FEL2019-THP001  
About • paper received ※ 20 August 2019       paper accepted ※ 25 August 2019       issue date ※ 05 November 2019  
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THP002 Beam Based Alignment in all Undulator Beamlines at European XFEL 592
 
  • M. Scholz, W. Decking
    DESY, Hamburg, Germany
  • Y. Li
    EuXFEL, Hamburg, Germany
 
  The Free Electron Laser European XFEL aims at delivering X-rays from 0.25 keV up to 25 keV out of three SASE undulators. A good overlap of photon and electron beams is indispensable to obtain good lasing performance, especially for the higher photon energies. Thus the quadrupole magnets in the undulators must be aligned as good as possible on a straight line. This can only be realized with a beam based alignment procedure. In this paper we will report on the method that was performed at the European XFEL. We will also discuss our results.  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-FEL2019-THP002  
About • paper received ※ 20 August 2019       paper accepted ※ 12 September 2019       issue date ※ 05 November 2019  
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THP003 Arbitrary Order Perturbation Theory for a Time-Discrete Model of Micro-Bunching Driven by Longitudinal Space Charge 596
 
  • Ph. Amstutz
    LBNL, Berkeley, California, USA
  • M. Vogt
    DESY, Hamburg, Germany
 
  A well established model for studying the micro-bunching instability driven by longitudinal space charge in ultra-relativistic bunches in FEL-like beamlines can be identified as a time-discrete Vlasov system with general drift maps and Poisson type collective kick maps. Here we present an arbitrary order perturbative approach for the general system and the complete all-orders solution for a special example. For this example we benchmark our theory against our Perron-Frobenius tree-code.  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-FEL2019-THP003  
About • paper received ※ 20 August 2019       paper accepted ※ 29 August 2019       issue date ※ 05 November 2019  
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THP007 Frequency-Detuning Dependent Transient Coaxial RF Coupler Kick 599
 
  • Y. Chen, J.D. Good, M. Groß, P.W. Huang, I.I. Isaev, C. Koschitzki, M. Krasilnikov, S. Lal, X. Li, O. Lishilin, G. Loisch, D. Melkumyan, R. Niemczyk, A. Oppelt, H.J. Qian, H. Shaker, G. Shu, F. Stephan, G. Vashchenko
    DESY Zeuthen, Zeuthen, Germany
  • F. Brinker, W. Decking
    DESY, Hamburg, Germany
 
  We model and characterize a transverse kick which results from the coaxial RF coupler in the L-band RF gun at the Photo Injector Test Facility at DESY in Zeuthen (PITZ). The RF pulse is typically 600 µs long and used to produce a train of up to 2700 electron bunches. The kick is transient and found to be dependent on the detuning of the resonance frequency of the gun cavity. The frequency detuning within the RF macro-pulse results in a variation in the kick strength along the pulse. This leads to a downstream orbit and size change of individual bunches within the train. Using 3D RF field distributions calculated at detuned frequencies of the cavity, particle tracking simulations are performed to simulate the transient kick onto the bunch train. Given a drift distance, the orbit and size change along a train of fixed length is estimated. Systematic measurements of the kick have meanwhile been carried out. The temperature of the cooling water for the gun is tuned allowing detailed characterization of the frequency detuning within the RF pulse, and thereby measurements of the kick under conditions of practical interest. Experimental findings and simulation results will be presented.  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-FEL2019-THP007  
About • paper received ※ 13 August 2019       paper accepted ※ 27 August 2019       issue date ※ 05 November 2019  
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THP008 Design of a Multi-Cell SRF Reduced-Beta Cavity for the Acceleration of Low Energy Electron Beams 603
 
  • D.B. Bazyl, H. De Gersem, W.F.O. Müller
    TEMF, TU Darmstadt, Darmstadt, Germany
  • J. Enders, S. Weih
    TU Darmstadt, Darmstadt, Germany
 
  Funding: Work supported by DFG (GRK 2128)
Recently, the S-DALINAC has successfully passed the first ERL tests. One of the critical requirements for further operation in the ERL regime is minimising the longitudinal energy spread of the electron beam. One of the major sources for the current energy spread at the S-DALINAC is the low energy accelerating section. In order to overcome this problem an SRF reduced-beta cavity has been designed. The new cavity will replace the existing capture section and will allow to accelerate low energy electron beams with a minimised energy spread growth. In this work we discuss the electromagnetic and mechanical design of the SRF 3 GHz 6-cell reduced-beta cavity of elliptic type. In addition, we present the results of beam dynamics simulations.
 
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-FEL2019-THP008  
About • paper received ※ 19 August 2019       paper accepted ※ 28 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 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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THP010 Simple and Robust Free Electron Laser Doubler 609
 
  • S. Di Mitri, G. De Ninno, R. Fabris, S. Spampinati
    Elettra-Sincrotrone Trieste S.C.p.A., Basovizza, Italy
  • G. De Ninno
    University of Nova Gorica, Nova Gorica, Slovenia
  • N. Thompson
    STFC/DL/ASTeC, Daresbury, Warrington, Cheshire, United Kingdom
  • N. Thompson
    Cockcroft Institute, Warrington, Cheshire, United Kingdom
 
  Funding: This work has received funding by the European Union’s Horizon 2020 research and innovation programme under Grant Agreement No. 777431.
We present the design of a Free-Electron Laser (FEL) doubler suitable for the simultaneous operation of two FEL lines. The doubler relies on the physical selection of two longitudinal portions of an electron bunch at low energy, and on their spatial separation at high energy. Since the two electron beamlets are naturally synchronized, FEL pump-FEL probe experiments are enabled when the two photon pulses are sent to the same experimental station. The proposed solution offers improved flexibility of operation w.r.t. existing two-pulse, two-color FEL schemes, and allows for independent control of the color, timing, intensity and angle of incidence of the radiation pulses at the user end station. Detailed numerical simulations demonstrate its feasibility at the FERMI FEL facility.
 
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-FEL2019-THP010  
About • paper received ※ 29 July 2019       paper accepted ※ 12 September 2019       issue date ※ 05 November 2019  
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THP011 Experimental Benchmarking of Wakefields at the FERMI FEL Linac and Undulator Line 613
 
  • S. Di Mitri, L. Sturari
    Elettra-Sincrotrone Trieste S.C.p.A., Basovizza, Italy
  • C. Venier, R. Vescovo
    University of Trieste, Trieste, Italy
 
  Collective effects such as wakefields affect the dynamics of high brightness electron beams in linear accelerators (linacs), and can degrade the performance of short wavelength free-electron lasers (FELs). If a reliable model of wakefields is made available, the accelerator can be designed and configured with parameters that minimize their disrupting effect. In this work, the simulated effect of geometric (diffractive) wakefields and of coherent synchrotron radiation on the electron beam energy distribution at the FERMI FEL is benchmarked with measurements, so quantifying the accuracy of the model. Wakefields modelling is then extended to the undulator line, where particle tracking confirms the limited impact of the resistive wall wakefield on the lasing process. The study reveals an overall good understanding of collective effects in the facility [1].
[1] S. Di Mitri et al., Phys. Rev. Accel. and Beams, 22, 014401 (2019)
 
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-FEL2019-THP011  
About • paper received ※ 29 July 2019       paper accepted ※ 25 August 2019       issue date ※ 05 November 2019  
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THP015 The X-Band Linear Compression System in Dalian Coherent Light Source 625
 
  • Y. Yu, Z. Chen, G.K. Cheng, D.X. Dai, H.L. Ding, Z.G. He, L. Huang, Q.M. Li, Z.B. Li, L. Shi, J.T. Sun, K. Tao, Y.H. Tian, G.L. Wang, Z.Q. Wang, G.R. Wu, J.Y. Yang, X.M. Yang, W.Q. Zhang
    DICP, Dalian, People’s Republic of China
 
  Dalian Coherent Light Source (DCLS) is a free-electron laser (FEL) user facility working in the extreme ultraviolet (EUV) wavelength region from 50 to 150 nm. It mainly operates on the High Gain Harmonic Generation (HGHG) mode with the seed laser, although it can also run in the Self Amplified Spontaneous Emission (SASE) mode. The brightness and bandwidth of FEL radiation strongly depends on electron bunch quality, such as normalized transverse emittance, electron bunch energy, energy spread, peak current, etc. The high peak current with uniform longitudinal distribution is especially helpful for high peak power and narrow bandwidth of FEL, although it is not easy to achieve, due to the nonlinearity of sinusoidal accelerating radio frequency (RF) field and the 2nd-order momentum compaction coefficient T566 of bunch compressor. An X-band linearizer will be installed before the bunch compressor in order to correct this nonlinearity properly. In this paper, the beam dynamics design of the X-band linear compression system in DCLS is focused, and the simulation results with Elegant are presented and discussed.  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-FEL2019-THP015  
About • paper received ※ 19 August 2019       paper accepted ※ 25 August 2019       issue date ※ 05 November 2019  
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THP016 Study of Microbunching Instability in SHINE Linac 629
 
  • D. Huang
    SINAP, Shanghai, People’s Republic of China
  • D. Gu
    SARI-CAS, Pudong, Shanghai, People’s Republic of China
  • M. Zhang
    Shanghai Advanced Research Institute, Pudong, Shanghai, People’s Republic of China
 
  The SHINE project in China aims at the next generation high repetation rate and high power hard X-ray free electron laser facility. The high quality electron beam is thus requested in the linac to generate such a high quality FEL lasing. As the prerequisite, the microbuncing instability introduced by the nonlinear effects such as the LSC, CSR and wakefields in the bunch compressing process must be taken care of, otherwise the electron beam will not meet the requirements of lasing. In this article, the microbunching effects including the gain of the instability in the linac of SHINE are estimated, and several ways for the control of the instability are proposed.  
poster icon Poster THP016 [0.536 MB]  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-FEL2019-THP016  
About • paper received ※ 24 August 2019       paper accepted ※ 29 August 2019       issue date ※ 05 November 2019  
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THP018 Transverse Deflecting Structure Dynamics for Time-Resolved Machine Studies of Shine 632
 
  • J.W. Yan, H.X. Deng, B. Liu, D. Wang
    SINAP, Shanghai, People’s Republic of China
  • H.X. Deng, B. Liu, D. Wang
    SARI-CAS, Pudong, Shanghai, People’s Republic of China
 
  Funding: National Natural Science Foundation of China (11775293), the National Key Research and Development Program of China (2016YFA0401900) and Ten Thousand Talent Program.
The transverse deflecting structure (TDS) has been widely used in modern free electron laser facilities for the longitudinal phase space diagnostics of electron beams. As the first hard x-ray free electron laser in China, the SHINE is designed to deliver photons with a repetition rate up to 1 MHz. In this paper, we present the beam dynamics study of the X-band TDS behind the undulator of SHINE. In order to prevent the screen from being damaged by electron bunches with a high repetition rate, the phase of the transverse deflecting cavity is designed to deviate from zero, and only those electron bunches that are kicked by the transverse deflecting cavity are sent to the screen. In addition, the evolutionary algorithm is introduced to optimize the lattice of the TDS line to reach the highest possible resolution.
 
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-FEL2019-THP018  
About • paper received ※ 19 August 2019       paper accepted ※ 28 August 2019       issue date ※ 05 November 2019  
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THP020 Microbunching Enhancement by Adiabatic Trapping 635
 
  • X.J. Deng, W.-H. Huang, C.-X. Tang
    TUB, Beijing, People’s Republic of China
  • A. Chao
    SLAC, Menlo Park, California, USA
 
  Storage ring based concept called steady-state microbunching was proposed years ago for high average power narrowband coherent radiation generation. There are now active efforts on-going by the SSMB collaboration established among Tsinghua University and several other institutes. In this paper we study the particle trap and filamentation process of beam in RF or Micro Bucket which is useful for understanding the injection beam dynamics of SSMB. One remarkable result is the steady-state current distribution after full filamentation has little dependence on the bucket height as long as it is several times larger than the energy spread. A discrete increase of bucket height can boost the bunching, with the sacrifice of emittance growth. An adiabatic change of bucket height from a smaller value to the final desired value is then proposed to boost the bunching while preserving the longitudinal emittance.  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-FEL2019-THP020  
About • paper received ※ 20 August 2019       paper accepted ※ 28 August 2019       issue date ※ 05 November 2019  
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THP022 A General Optimization Method for High Harmonic Generation Beamline 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 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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THP027 Simulation and Optimization of the Transport Beamline for the NovoFEL RF Gun 647
 
  • A.S. Matveev, I.V. Davidyuk, O.A. Shevchenko, V.G. Tcheskidov, N.A. Vinokurov, V. Volkov
    BINP SB RAS, Novosibirsk, Russia
  • I.V. Davidyuk, A.S. Matveev, N.A. Vinokurov
    NSU, Novosibirsk, Russia
 
  A new low-frequency CW RF gun was developed and tested at Budker Institute of Nuclear Physics recently. We plan to use it to upgrade the ERL of the Novosibirsk FEL facility. It will allow increasing the average beam current (due to higher beam repetition rate) and thus increasing the average radiation power. The transport beamline for the RF gun uses the ninety-degree achromatic bend. It is designed in a way that keeps an option to operate with the old electrostatic gun as well. Due to the low beam energy (290 keV) the beam dynamics is strongly influenced by space-charge forces. The paper describes results of simulation and optimization of the RF gun transport beamline. Space-charge forces were taken into account with the code ASTRA. Main sources of emittance degradation were considered in order to decrease their influence during the optimization. In addition, the RF gun output beam parameters were measured for various RF gun emission phases. These experiments were simulated and the results were compared. The resulting beam parameters meets requirements of the Novosibirsk FEL facility ERL.  
poster icon Poster THP027 [3.158 MB]  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-FEL2019-THP027  
About • paper received ※ 16 August 2019       paper accepted ※ 27 August 2019       issue date ※ 05 November 2019  
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THP031 Simulation and Optimization of Injector System for the Pre-bunched THz FEL 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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THP033 XFEL Isochronous Chicanes: Feasibility Study 658
 
  • N. Thompson
    STFC/DL/ASTeC, Daresbury, Warrington, Cheshire, United Kingdom
 
  FEL schemes such as High-Brightness SASE [1] and Mode-Locking [2] require electron beam delays inserted between undulator sections. These schemes have been shown in simulations to perform most effectively when the electron beam delays are very close to isochronous, i.e. the first order longitudinal dispersion is very small. To minimise the disruption to the FEL process in the inter-undulator gaps, these delays must also be as compact as possible. In this paper we study the maximum longitudinal space that a delay chicane could occupy in an XFEL operating at 6 GeV before the peak power drops below a defined threshold, and we present a limit for the maximum longitudinal dispersion of the delay chicanes. We then present the optical designs of two chicanes that satisfy the requirements of length and isochronicity and show how these designs could be realised practically using small-aperture high-field quadrupoles.
[1] PRL 110, 134802 (2013).
[2] PRL 100, 203901 (2008).
 
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-FEL2019-THP033  
About • paper received ※ 16 August 2019       paper accepted ※ 09 September 2019       issue date ※ 05 November 2019  
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THP035 Beam Shaping for High-Repetition-Rate X-Ray FELs 661
 
  • Y. Ding, K.L.F. Bane, Y.M. Nosochkov
    SLAC, Menlo Park, California, USA
 
  Beam shaping at normal-conducting, accelerator-based FELs, such as LCLS, plays an important role for improving lasing performance and for supporting special operating modes, such as the self-seeding scheme. Beam shaping methods include horn-collimation and dechirper manipulation. Applying the beam shaping concept to high-repetition-rate FELs driven by a superconducting linac, such as LCLS-II, beam invasive methods are not preferred due to concerns about high power deposition. We have recently studied a few shaping options for LCLS-II, such as manipulating the beam chirp before compression using corrugated devices, and modifying higher order optics terms in a chicane using octupoles. In this report we will discuss the results.  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-FEL2019-THP035  
About • paper received ※ 23 August 2019       paper accepted ※ 28 August 2019       issue date ※ 05 November 2019  
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THP036 Microbunch Rotation for Hard X-Ray Beam Multiplexing 665
 
  • R.A. Margraf, Z. Huang, J.P. MacArthur, G. Marcus
    SLAC, Menlo Park, California, USA
  • X.J. Deng
    TUB, Beijing, People’s Republic of China
  • Z. Huang, J.P. MacArthur, R.A. Margraf
    Stanford University, Stanford, California, USA
 
  Funding: This work was supported by the Department of Energy, Laboratory Directed Research and Development program at SLAC National Accelerator Laboratory, under contract DE-AC02-76SF00515.
Electron bunches in an undulator develop periodic density modulations, or microbunches, which enable the exponential gain of X-ray power in a SASE FEL. Many FEL applications could benefit from the ability to preserve microbunching through a dipole kick. For example, X-ray beam multiplexing can be achieved if electron bunches are kicked into separate beamlines and allowed to lase in a final undulator. The microbunches developed in upstream undulators, if properly rotated, will lase off axis, producing radiation at an angle offset from the initial beam axis. Microbunch rotation with soft X-rays was previously published and demonstrated experimentally [1], multiplexing LCLS into three X-ray beams. Additional 2018 data demonstrated multiplexing of hard X-rays. Here we describe efforts to reproduce these hard X-ray experiments using an analytical model and Genesis simulations. Our goal is to apply microbunch rotation to out-coupling from a cavity-based XFEL, (RAFEL/XFELO) [2].
[1] J. P. MacArthur et al., Physical Review X 8, 041036 (2018).
[2] G. Marcus et al. Poster TUD04 presented at FEL2019 (2019).
 
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-FEL2019-THP036  
About • paper received ※ 24 August 2019       paper accepted ※ 26 August 2019       issue date ※ 05 November 2019  
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THP037 A Novel One-Dimensional Model for CSR Wakefields 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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