Keyword: cavity
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MOA07 Commissioning and First Lasing of the FELiChEM: A New IR and THz FEL Oscillator in China FEL, electron, undulator, linac 15
 
  • H.T. Li, Q.K. Jia
    USTC/NSRL, Hefei, Anhui, People’s Republic of China
  
  A new infrared FEL named FELiChEM aiming at the energy chemistry has been constructed and commissioned at NSRL in Hefei. It consists of two FEL oscillators driven by one normal-conducting S-Band linac with maximum beam energy of 60 MeV. The two oscillators generate the midinfrared and far-infrared lasers covering the spectral range of 2.5-50 µm and 40-200 µm, respectively. First lasing was achieved at a wavelength of 15 µm with an electron energy of 35 MeV. Till now, we have observed the FEL signal from 3.5 µm to 30 µm and achieved the maximum micropulse energy up to 27 µJ at 15 µm.  
slides icon Slides MOA07 [2.434 MB]  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-FEL2019-MOA07  
About • paper received ※ 20 August 2019       paper accepted ※ 28 August 2019       issue date ※ 05 November 2019  
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MOC01 Regenerative Amplifier FEL - from IR to X-Rays FEL, undulator, electron, feedback 20
 
  • D.C. Nguyen, P.M. Anisimov, C.E. Buechler, Q.R. Marksteiner, R.L. Sheffield
    LANL, Los Alamos, New Mexico, USA
  
  The Regenerative Amplifier FEL (RAFEL) feeds back a small fraction of the radiation exiting a high-gain undulator as the seed for the next pass, and achieves narrow linewidth and saturation in a few passes. For the IR RAFEL, we used an optical cavity with annular mirrors to reinject ~10% of the IR radiation back into a two-meter undulator [1]. Since then, a number of researchers have proposed RAFEL and XFELO to achieve full temporal coherence in VUV and X-ray FELs [2-5]. For the XFELO, symmetric Bragg backscattering off high-quality diamond crystals can provide very high reflectivity for the XFELO cavity [6]. The required reflectivity for a RAFEL feedback cavity is much lower than the XFELO. We show that 6% feedback is sufficient for the X-ray RAFEL at 9.8 keV to saturate and achieve 0.5-eV bandwidth. We discuss options to out-couple more than ~50% of the RAFEL intra-cavity power and discuss challenges associated with X-ray absorption in the out-coupler.
[1] D. Nguyen et al. NIMA 429 125 (1999)
[2] B. Faatz et al. NIMA A429 424 (1999)
[3] Z. Huang et al. PRL 96 144801 (2006)
[4] B.W.J. McNeil et al. NJP 9 239 (2007)
[5] G. Marcus et al. FEL17 MOP061 (2017)
[6] K. Kim et al. PRL 100 244802 (2008) 		 
slides icon Slides MOC01 [1.260 MB]  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-FEL2019-MOC01  
About • paper received ※ 21 August 2019       paper accepted ※ 28 August 2019       issue date ※ 05 November 2019  
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TUP006 The FHI FEL Upgrade Design FEL, undulator, dipole, kicker 52
 
  • W. Schöllkopf, M. De Pas, D. Dowell, S. Gewinner, H. Junkes, G. Meijer, G. von Helden
    FHI, Berlin, Germany
  • W.B. Colson
    NPS, Monterey, California, USA
  • S.C. Gottschalk
    STI Magnetics LLC, Woodinville, USA
  • J. Rathke, T. Schultheiss
    AES, Medford, New York, USA
  • A.M.M. Todd
    AMMTodd Consulting, Princeton Junction, New Jersey, USA
  • L.M. Young
    LMY Technology, Lincolnton, Georgia, USA
  
  Since coming on-line in November 2013, the Fritz-Haber-Institut (FHI) der Max-Planck-Gesellschaft (MPG) Free-Electron Laser (FEL) has provided intense, tunable infrared radiation to FHI user groups. It has enabled experiments in diverse fields ranging from bio-molecular spectroscopy to studies of clusters and nanoparticles, nonlinear solid-state spectroscopy, and surface science, resulting in 50 peer-reviewed publications so far. A significant upgrade of the FHI FEL is now being prepared. A second short Rayleigh range undulator FEL beamline is being added that will permit lasing from < 5 microns to > 160 microns. Additionally, a 500 MHz kicker cavity will permit simultaneous two-color operation of the FEL from both FEL beamlines over an optical range of 5 to 50 microns by deflecting alternate 1 GHz pulses into each of the two undulators. We will describe the upgraded FHI FEL physics and engineering design and present the plans for two-color FEL operations in November 2020.  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-FEL2019-TUP006  
About • paper received ※ 20 August 2019       paper accepted ※ 27 August 2019       issue date ※ 05 November 2019  
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TUP009 Integration of an XFELO at the European XFEL Facility FEL, electron, radiation, simulation 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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TUP020 Terahertz Free Electron Maser Based on Excitation of a Talbot-Type Super-Mode in an Oversized Microwave System electron, GUI, resonance, simulation 87
 
  • A.V. Savilov, Yu.S. Oparina, N.Yu. Peskov
    IAP/RAS, Nizhny Novgorod, Russia
  
  Funding: The work is supported by the Russian Science Foundation, Project # 19-12-00212.
A natural problem arising in the case of realization of a THz FEM with a high-current relativistic e-beam is an inevitable use of an oversized microwave system, which characteristic transverse size significantly exceeds the wavelength of the operating wave. In this situation, it becomes difficult to provide selective excitation of a chosen transverse mode of the operating cavity. Our basic idea is to give up working on a fixed transverse mode. Instead, we propose to work on a supermode, which is a fixed set of several transverse modes of an oversized wavegude. We propose to use the Talbot effect [1,2,3] as a way to create an oversized microwave system of an electron maser that provides a high Q-factor for this supermode. On the basis of a multi-mode set of self-consistent equations of the electron-wave interaction we demonstrate the possibility of the selective self-excitation of the supermode both in the simplest 2-D model and in the detailed modeling of a THz FEM fed by a 10 MeV / 2 kA / 200 e-beam based on excitation of a Talbot-type supermode at a frequency close to 2 THz. The calculated efficiency at the level of 5-10% corresponds to the GW level of the output power.
[1] L. A. Rivlin, Laser Focus, p. 82, 1981
[2] G. G. Denisov, D. A. Lukovnikov, M. Yu. Shmelyov, Digest of 18 Int. Conf. on IR MM Waves, p. 485, 1993
[3] V. L. Bratman et al., Nucl. Instr. Meth. Phys. Res. A, vol. 407, pp. 40-44, 1998 		 
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-FEL2019-TUP020  
About • paper received ※ 14 August 2019       paper accepted ※ 27 August 2019       issue date ※ 05 November 2019  
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TUP025 Current Status of Free Electron Laser @ TARLA FEL, electron, cryomodule, undulator 102
 
  • A. Aksoy, Ö. Karslı, C. Kaya, İ.B. Koç
    Ankara University, Accelerator Technologies Institute, Golbasi, Turkey
  • Ö.F. Elçim
    Ankara University Institute of Accelerator Technologies, Golbasi, Turkey
  
  Funding: Work supported by Strategy and Budget Department of Turkey with Grand No: 2006K120470
Turkish Accelerator and Radiation Laboratory (TARLA), which is supported by the Presidency Strategy and Budget Directorate of Turkey, aims to be the state of art research instrument for the radiation users from Turkey. Two superconducting accelerating modules of TARLA will drive two different planar undulator magnets with periods of 110 mm (U110) and 35 mm (U35) in order to generate high brightness Continuous Wave (CW) Free Electron Laser (FEL) tunable in between 5-350 µm. In addition, the linac will drive a Bremstrahlung radiation station to generate polarized gamma radiation. Main components of TARLA, such as injector, superconducting accelerating modules and cryoplant are under commissioning currently. In this study, we present current status of the facility in addition to expected FEL performance of the facility. 		 
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-FEL2019-TUP025  
About • paper received ※ 20 August 2019       paper accepted ※ 29 August 2019       issue date ※ 05 November 2019  
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TUP026 Unaveraged Simulation of a Regenerative Amplifier Free Electron Laser FEL, undulator, simulation, electron 106
 
  • P. Pongchalee, B.W.J. MᶜNeil
    USTRAT/SUPA, Glasgow, United Kingdom
  • B.W.J. MᶜNeil
    Cockcroft Institute, Warrington, Cheshire, United Kingdom
  
  A regenerative amplifier free-electron laser (RAFEL) design and simulation requires the modelling of both the electron-light interaction in the FEL undulator and the optical propagation within the cavity. An unaveraged 3D simulation was used to model the FEL interaction within the undulator using the Puffin code. This allows a broadband, high temporal-resolution of the FEL interaction. The Optical Propagation Code (OPC) was used to model the optical beam propagation within the cavity and diagnostics at the cavity mirrors. This paper presents the optical field conversion method between Puffin and the OPC codes and demonstrates the full model via a VUV-RAFEL simulation.  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-FEL2019-TUP026  
About • paper received ※ 19 August 2019       paper accepted ※ 25 August 2019       issue date ※ 05 November 2019  
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TUP027 Modelling Crystal Misaligments for the X-ray FEL Oscillator FEL, alignment, undulator, simulation 110
 
  • R.R. Lindberg
    ANL, Lemont, Illinois, USA
  
  Funding: Work supported by U.S. Dept. of Energy Office of Sciences under Contract No. DE-AC02-06CH11357.
The X-ray FEL oscillator has the potential to be a revolutionary new light source providing unprecedented stability in a narrow bandwidth [1]. However, a detailed understanding of cavity tolerance and stability has only begun, and there are presently no suitable simulation tools. To address this issue, we have developed a fast FEL oscillator code that discretizes the field using a Gauss-Hermite mode expansion of the oscillator cavity. Errors in crystal alignment result in a mixing of the modes that is easily modeled with a loss and coupling matrix. We show first results from our code, including the effects of static and time-varying crystal misalignments.
[1] K.-J. Kim, Y. Shvyd’ko, and S. Reiche, PRL 100 244802 (2008) 		 
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-FEL2019-TUP027  
About • paper received ※ 20 August 2019       paper accepted ※ 25 August 2019       issue date ※ 05 November 2019  
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TUP028 Power Variations of an X-ray FEL Oscillator in Saturation FEL, electron, simulation, undulator 114
 
  • R.R. Lindberg, K. Kim
    ANL, Lemont, Illinois, USA
  
  Funding: Work supported by U.S. Dept. of Energy Office of Sciences under Contract No. DE-AC02-06CH11357.
Basic FEL theory predicts that the fractional power fluctuations of an ideal oscillator in steady state should be given by the ratio of the spontaneous power in the oscillator bandwidth to that stored in the cavity at saturation. For the X-ray FEL oscillator with its narrow bandwidth Bragg crystal mirrors, this ratio is typically a few parts per million, but some simulations have shown evidence of power oscillations on the percent level. We show that this is not related to the well-known sideband instability, but rather is purely numerical and can be eliminated by changing the particle loading. We then briefly discuss to what extent variations in electron beam arrival time may degrade the power stability. 		 
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-FEL2019-TUP028  
About • paper received ※ 20 August 2019       paper accepted ※ 25 August 2019       issue date ※ 05 November 2019  
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TUP032 Regenerative Amplification for a Hard X-Ray Free-Electron Laser FEL, electron, radiation, undulator 118
 
  • G. Marcus, Y. Ding, Y. Feng, A. Halavanau, Z. Huang, J. Krzywiński, J.P. MacArthur, R.A. Margraf, T.O. Raubenheimer, D. Zhu
    SLAC, Menlo Park, California, USA
  • V. Fiadonu
    Santa Clara University, Santa Clara, California, USA
  
  Funding: This work was supported by the Department of Energy, Laboratory Directed Research and Development program at SLAC National Accelerator Laboratory, under contract DE-AC02-76SF00515.
An X-ray regenerative amplifier FEL (XRAFEL) utilizes an X-ray crystal cavity to provide optical feedback to the entrance of a high-gain undulator. An XRAFEL system leverages gain-guiding in the undulator to reduce the cavity alignment tolerances and targets the production of longitudinally coherent and high peak power and brightness X-ray pulses that could significantly enhance the performance of a standard single-pass SASE amplifier. The successful implementation of an X-ray cavity in the XRAFEL scheme requires the demonstration of X-ray optical components that can either satisfy large output coupling constraints or passively output a large fraction of the amplified coherent radiation. Here, we present new schemes to either actively Q-switch a diamond Bragg crystal through lattice constant manipulation or passively output couple a large fraction of the stored cavity radiation through controlled FEL microbunch rotation. A beamline design study, cavity stability analysis, and optimization will be presented illustrating the performance of potential XRAFEL configurations at LCLS-II/-HE using high-fidelity simulations. 		 
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-FEL2019-TUP032  
About • paper received ※ 24 August 2019       paper accepted ※ 26 August 2019       issue date ※ 05 November 2019  
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TUP033 Q-Switching of X-Ray Optical Cavities by Using Boron Doped Buried Layer Under a Surface of a Diamond Crystal laser, FEL, electron, free-electron-laser 122
 
  • J. Krzywiński, Y. Feng, A. Halavanau, Z. Huang, A.M. Kiss, J.P. MacArthur, G. Marcus, T. Sato, D. Zhu
    SLAC, Menlo Park, California, USA
  
  Improvement of the longitudinal coherence of X-ray Free Electron Lasers has been the subject of many recent investigations. The XFEL oscillator (XFELO) and Regenerative Amplifier Free-Electron Laser (RAFEL) schemes offer a pathway to fully coherent, high brightness X-ray radiation. The XFELO and RAFEL consist of a high repetition rate electron beam, an undulator and an X-ray crystal cavity to provide optical feedback. The X-ray cavity will be based on diamond crystals in order to manage a high thermal load. We are investigating a ’Q switching’ mechanism that involves the use of a ’Bragg switch’ to dump the X-ray pulse energy built-up inside an X-ray cavity. In particular, one can use an optical laser to manipulate the diamond crystal lattice constant to control the crystal reflectivity and transmission. It has been shown that a 9 MeV focused boron beam can create a buried layer, approximately 5 microns below surface, with a boron concentration up to 1021 atoms/cm3. Here, we present simulations showing that absorbing laser pulses by a buried layer under the crystal surface would allow creating a transient temperature profile which would be well suited for the ’Q switching’ scheme.  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-FEL2019-TUP033  
About • paper received ※ 21 August 2019       paper accepted ※ 29 August 2019       issue date ※ 05 November 2019  
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TUP053 An Investigation of Possible Non-Standard Photon Statistics in a Free-Electron Laser I: Experiment photon, FEL, experiment, radiation 161
 
  • J.-W. Park
    University of Hawaii, Honolulu,, USA
  • K.-J. Kim, R.R. Lindberg
    ANL, Lemont, Illinois, USA
  
  Funding: Work supported by U.S. DOE, Office of Science, Office of BES, under Award No. DE-SC0018428.
It was reported that the photon statistics of the seventh coherent spontaneous harmonic radiation of the MARK III FEL was sub-Poissonian [1], which concludes that Fano factor F (the ratio of photon number variance to the average photon number) is less than unity. Whether FEL light exhibits such non-standard behavior is an important issue; if it does, our understanding of the FEL needs to be radically modified. In this paper, we re-examine the analyses of experimental data in Ref. [1]. We find that the observed value of F could be explained within the standard FEL theory if one combines the detector dead time effect with photon clustering arising from the FEL gain. We propose an improved experiment for a more definitive measurement of the FEL photon statistics.
[1] T. Chen and J.M. Madey, J. Phys. Rev. Lett. 86, 5906 (2001). 		 
poster 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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TUP073 High-Repetition-Rate Seeding Schemes Using a Resonator-Amplifier Setup FEL, laser, electron, radiation 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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TUD02 Application of Infrared FEL Oscillators for Producing Isolated Attosecond X-Ray Pulses via High-Harmonic Generation in Rare Gases FEL, laser, experiment, photon 272
 
  • R. Hajima, K. Kawase, R. Nagai
    QST, Tokai, Japan
  • Y. Hayakawa, T. Sakai, Y. Sumitomo
    LEBRA, Funabashi, Japan
  • T. Miyajima, M. Shimada
    KEK, Ibaraki, Japan
  • H. Ohgaki, H. Zen
    Kyoto University, Kyoto, Japan
  
  Funding: Quantum Leap Flagship Program (MEXT Q-LEAP)
High harmonic generation (HHG) in rare gases is now becoming a common technology to produce attosecond pulses in VUV wavelengths. So far HHG sources have been realized by femtosecond solid-state lasers, not FELs. We propose a FEL-driven HHG source to explore attosecond pulses at photon energies above 1 keV with a MHz-repetition, which is difficult with solid-state lasers [1]. A research program has been launched to establish technologies for the FEL-HHG, which covers generation and characterization of few-cycle IR pulses in a FEL oscillator, stacking of FEL pulses in an external cavity, and a seed laser for stabilization of carrier-envelope phase in a FEL oscillator. In this talk, we present the scheme of FEL-HHG and the status of the research program.
[1] R. Hajima and R. Nagai, Phys. Rev. Lett. 119, 204802 (2017) 		 
slides icon Slides TUD02 [8.995 MB]  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-FEL2019-TUD02  
About • paper received ※ 23 August 2019       paper accepted ※ 29 August 2019       issue date ※ 05 November 2019  
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TUD04 Cavity-Based Free-Electron Laser Research and Development: A Joint Argonne National Laboratory and SLAC National Laboratory Collaboration FEL, electron, undulator, laser 282
 
  • G. Marcus, F.-J. Decker, G.L. Gassner, A. Halavanau, J.B. Hastings, Z. Huang, Y. Liu, J.P. MacArthur, R.A. Margraf, T.O. Raubenheimer, A. Sakdinawat, T.-F. Tan, D. Zhu
    SLAC, Menlo Park, California, USA
  • J.W.J. Anton, L. Assoufid, K. Goetze, W.G. Jansma, S.P. Kearney, K. Kim, R.R. Lindberg, A. Miceli, X. Shi, D. Shu, Yu. Shvyd’ko, J.P. Sullivan, M. White
    ANL, Lemont, Illinois, USA
  • B. Lantz
    Stanford University, Stanford, California, USA
  
  One solution for producing longitudinally coherent FEL pulses is to store and recirculate the output of an amplifier in an X-ray cavity so that the X-ray pulse can interact with following fresh electron bunches over many passes. The X-ray FEL oscillator (XFELO) and the X-ray regenerative amplifier FEL (XRAFEL) concepts use this technique and rely on the same fundamental ingredients to realize their full capability. Both schemes require a high repetition rate electron beam, an undulator to provide FEL gain, and an X-ray cavity to recirculate and monochromatize the radiation. The shared infrastructure, complementary performance characteristics, and potentially transformative FEL properties of the XFELO and XRAFEL have brought together a joint Argonne National Laboratory (ANL) and SLAC National Laboratory (SLAC) collaboration aimed at enabling these schemes at LCLS-II. We present plans to install a rectangular X-ray cavity in the LCLS-II undulator hall and perform experiments employing 2-bunch copper RF linac accelerated electron beams. This includes performing cavity ring-down measurements and 2-pass gain measurements for both the low-gain XFELO and the high-gain RAFEL schemes.  
slides icon Slides TUD04 [12.425 MB]  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-FEL2019-TUD04  
About • paper received ※ 25 August 2019       paper accepted ※ 29 August 2019       issue date ※ 05 November 2019  
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WEP011 Longitudinal Intra-Train Beam-Based Feedback at FLASH feedback, controls, laser, electron 346
 
  • S. Pfeiffer, L. Butkowski, M.K. Czwalinna, B. Dursun, C. Gerth, B. Lautenschlager, H. Schlarb, Ch. Schmidt
    DESY, Hamburg, Germany
  
  The longitudinal intra-train beam-based feedback has been recommissioned after major upgrades on the synchronization system of the FLASH facility. Those upgrades include: new bunch arrival time monitors (BAMs), the optical synchronization system accommodating the latest European XFEL design based on PM fibers, and installation of a small broadband normal conducting RF cavity. The cavity is located prior to the first bunch compressor at FLASH and allows energy modulation bunch-by-bunch (1 us spacing) on the per mille range. Through the energy dependent path length of the succeeding magnetic chicane the cavity is used for ultimate bunch arrival time corrections. Recently the RF cavity operated 1 kW pulsed solid-state amplifier was successfully commissioned. First tests have been carried out incorporating the fast cavity as actuator together with SRF stations for larger corrections in our intra-train beam-based feedback pushing now arrival time stabilities towards 5 fs (rms). The latest results and observed residual instabilities are presented.  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-FEL2019-WEP011  
About • paper received ※ 20 August 2019       paper accepted ※ 17 September 2019       issue date ※ 05 November 2019  
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WEP024 1.3 GHz Solid State Power Amplifier for the Buncher in CTFEL Facility electron, experiment, FEL, bunching 371
 
  • T.H. He, C.L. Lao, P. Li, X. Luo, L.J. Shan, K. Zhou
    CAEP/IAE, Mianyang, Sichuan, People’s Republic of China
  
  The THz Free Electron Laser facility (CAEP THz FEL, CTFEL) of the China Academy of Engineering Physics uses high quality electron beams to generate high average power terahertz radiations. A 1.3 GHz RF buncher is used in front of the superconducting linear accelerator of the CTFEL facility to improve the electron beams quality. The RF buncher is driven by a solid state power amplifier (SSPA), and the SSPA is feedback controlled by a low level RF (LLRF) control system to ensure the high stability of the amplitude and phase of the bunching field in the buncher cavity. The SSPA operates at 1.3 GHz and outputs 0 to 5 kW of continuous wave power. This paper mainly introduces the principle and composition of the SSPA, and presents some experiments on the RF buncher driven by the SSPA.  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-FEL2019-WEP024  
About • paper received ※ 15 August 2019       paper accepted ※ 27 August 2019       issue date ※ 05 November 2019  
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WEP026 Preliminary Geometry Optimization of a 3.5-Cell SRF Gun Cavity at ELBE Based on Beam Dynamics SRF, gun, emittance, electron 374
 
  • K. Zhou, P. Li
    CAEP/IAE, Mianyang, Sichuan, People’s Republic of China
  • A. Arnold, S. Ma, J. Schaber, J. Teichert, R. Xiang
    HZDR, Dresden, Germany
  
  At present, ELBE radiation source at HZDR is optimizing the SRF cavity for the next generation ELBE SRF GUN. This paper presents a preliminary study on the geometry optimization of a 3.5-cell SRF gun cavity based on beam dynamics. By changing the lengths of the half cell and the first TESLA like cell, two new cavity models with higher electric field in the half cell are built and their RF fields are compared with SRF GUN I and SRF GUN II. Through the scanning of the RF phases and the electric fields, the simulation results indicate that new models have smaller transverse emittance at relatively lower electric field gradients and better performance on longitudinal emittance than SRF GUN I and SRF GUN II.  
poster icon Poster WEP026 [1.345 MB]  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-FEL2019-WEP026  
About • paper received ※ 19 August 2019       paper accepted ※ 29 August 2019       issue date ※ 05 November 2019  
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WEP036 The PolariX-TDS Project: Bead-Pull Measurements and High-Power Test on the Prototype polarization, FEL, electron, status 396
 
  • P. Craievich, M. Bopp, H.-H. Braun, A. Citterio, R. Ganter, T. Kleeb, F. Marcellini, M. Pedrozzi, E. Prat, S. Reiche
    PSI, Villigen PSI, Switzerland
  • R.W. Aßmann, F. Christie, R.T.P. D’Arcy, U. Dorda, M. Foese, P. Gonzalez Caminal, M. Hoffmann, M. Hüning, R. Jonas, O. Krebs, S. Lederer, V. Libov, B. Marchetti, D. Marx, J. Osterhoff, M. Reukauff, H. Schlarb, S. Schreiber, G. Tews, M. Vogt, A. Wagner
    DESY, Hamburg, Germany
  • N. Catalán Lasheras, A. Grudiev, G. McMonagle, W.L. Millar, S. Pitman, K.T. Szypula, W. Wuensch, V. del Pozo Romano
    CERN, Meyrin, Switzerland
  • W.L. Millar
    Cockcroft Institute, Warrington, Cheshire, United Kingdom
  
  A collaboration between DESY, PSI and CERN has been established to develop and build an advanced modular X- band transverse deflection structure (TDS) system with the new feature of providing variable polarization of the deflecting force. The prototype of the novel X-band TDS, the Polarizable X-band (PolariX) TDS, was fabricated at PSI following the high-precision tuning-free production process developed for the C-band Linac of the SwissFEL project. Bead-pull RF measurements were also performed at PSI to verify, in particular, that the polarization of the dipole fields does not have any rotation along the structure. The high-power test was performed at CERN and now the TDS is at DESY and has been installed in FLASHForward, where the first streaking experience with beam will be accomplished. We summarize in this paper the status of the project, the results of the bead-pull measurements and the high power test.  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-FEL2019-WEP036  
About • paper received ※ 21 August 2019       paper accepted ※ 26 August 2019       issue date ※ 05 November 2019  
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WEP042 Observations of Short-Range Wakefield Effects in TESLA-Type Superconducting RF Cavities HOM, wakefield, FEL, MMI 412
 
  • A.H. Lumpkin, D.R. Edstrom, J. Ruan, R.M. Thurman-Keup
    Fermilab, Batavia, Illinois, USA
  
  Funding: This manuscript has been authored by Fermi Research Alliance, LLC under Contract No. DE-AC02-07CH11359 with the U.S. Department of Energy, Office of Science, Office of High Energy Physics.
The accelerators for high power X-ray free-electron laser (FEL) facilities such as the European XFEL and planned LCLS-II X-ray FEL are employing TESLA-type SCRF cavities. Beam propagation off axis in these cavities can result in both short-range and long-range transverse wakefields which can lead to emittance dilution within the micropulses and macropulses, respectively. The Fermilab Accelerator Science and Technology (FAST) facility has a unique configuration of a photocathode RF gun beam injecting two TESLA-type single cavities (CC1 and CC2) in series prior to the cryomodule. To investigate short-range wakefield effects, we used a vertical corrector between these two cavities to steer the beam off axis at an angle into CC2. A Hamamatsu synchroscan streak camera viewing a downstream OTR screen provided an image of y-t effects within the micropulses with resolutions of ~10-micron spatial and 2-ps temporal. At 500 pC/b, 50 b, and 4 mrad off-axis steering, we observed an ~100-micron head-tail centroid shift in the streak camera image. This centroid shift is consistent with a calculated short-range wakefield effect. Additional results for kick-angle compensation will be presented. 		 
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-FEL2019-WEP042  
About • paper received ※ 20 August 2019       paper accepted ※ 28 August 2019       issue date ※ 05 November 2019  
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WEP054 Beam Dynamics Optimization of a Normal-Conducting Gun Based CW Injector for the European XFEL cathode, gun, FEL, cryomodule 452
 
  • H. Shaker, S. Lal, H.J. Qian, G. Shu, F. Stephan
    DESY Zeuthen, Zeuthen, Germany
  
  The European XFEL is operating up to 17.5 GeV electron energy with maximum 0.65% duty cycle. There is a prospect for continuous wave and long pulse mode (CW/LP) operation of the European XFEL, which enables more flexible bunch pattern time structure for experiments, higher average brightness and better stability. Due to engineering limitations, the maximum electron beam energy in the CW/LP mode is about 8.6/12.8 GeV, which puts more pressure on the injector beam quality for lasing at the shortest wavelength. This paper optimizes the beam dynamics of an injector based on a normal-conducting VHF gun.  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-FEL2019-WEP054  
About • paper received ※ 20 August 2019       paper accepted ※ 26 August 2019       issue date ※ 05 November 2019  
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WEP055 Multiphysics Analysis of a CW VHF Gun for European XFEL gun, simulation, FEL, vacuum 456
 
  • G. Shu, Y. Chen, S. Lal, H.J. Qian, H. Shaker, F. Stephan
    DESY Zeuthen, Zeuthen, Germany
  
  R&D for a possible future CW mode operation of European XFEL started after the successful commissioning of the pulse mode operation. For the CW electron source upgrade, a fully superconducting CW gun is under experimental development at DESY in Hamburg, and a normal conducting (NC) CW gun is under physics design at the Photo Injector Test facility at DESY in Zeuthen (PITZ) as a backup option. Based on the experience of the LBNL on a 187 MHz gun, the DESY 217 MHz gun increased the cathode gradient and RF power to 28 MV/m and 100 kW, respectively, to further improve the beam brightness. In this paper, the multiphysics analysis investigating the RF, thermal and mechanical properties of the 217 MHz NC CW gun are presented.  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-FEL2019-WEP055  
About • paper received ※ 20 August 2019       paper accepted ※ 28 August 2019       issue date ※ 05 November 2019  
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WEP056 Engineering Design of Low-Emittance DC-SRF Photocathode Injector SRF, cathode, linac, shielding 460
 
  • Y.Q. Liu, M. Chen, S. Huang, L. Lin, K.X. Liu, S.W. Quan, F. Wang, S. Zhao
    PKU, Beijing, People’s Republic of China
  
  An upgraded version of DC-SRF photocathode injector (DC-SRF-II) is under development at Peking University. The goal is to achieve an emittance below 0.5 mm-mrad at the bunch charge of 100 pC and repetition rate of 1 MHz. The engineering design of the DC-SRF-II photoinjector was accomplished in this May and the fabrication is ongoing now. This paper presents some details of the engineering design.  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-FEL2019-WEP056  
About • paper received ※ 19 August 2019       paper accepted ※ 26 August 2019       issue date ※ 05 November 2019  
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WEP057 Performance Optimization of Low-Emittance DC-SRF Injector Using Cs2Te Photocathode emittance, electron, SRF, solenoid 463
 
  • S. Zhao
    Peking University, Beijing, People’s Republic of China
  • S. Huang, K.X. Liu, Y.Q. Liu, D.M. Ouyang
    PKU, Beijing, People’s Republic of China
  
  A low-emittance DC-SRF injector (DC-SRF-II) is under construction at Peking University, in the earlier design of which K2CsSb photocathode was chosen. Recently we changed the cathode to Cs2Te, which is more widely used nowadays, and carried out a detailed performance optimization. In this paper, we present our latest simulation results, which show that an emittance under 0.5 mm-mrad can be achieved at the bunch charge of 100 pC.  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-FEL2019-WEP057  
About • paper received ※ 14 August 2019       paper accepted ※ 27 August 2019       issue date ※ 05 November 2019  
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WEP059 Characterizing a Coherent Electron Source Extracted From a Cold Atom Trap electron, emittance, controls, laser 469
 
  • H. Luo, P.X. Chu, J. Guo, T. Liu, Y.X. Xu, X. Zhao
    SWUST, Mianyang City, Sichuan Province, People’s Republic of China
  • X.H. Li, Q.H. Zhou
    Southwest University of Science and Technology, Mianyang, Sichuan, People’s Republic of China
  • K. Wang
    USTC, Hefei, Anhui, People’s Republic of China
  
  Funding: The National Natural Science Foundation of China under Grant No. 11875227.
In order to generate a fully coherent free electron laser (FEL) within a compact system, one approach is to interact a coherent electron bunch with a high power laser operating in the quantum FEL regime. The coherent electron source is obtained by ionizing the Rydberg atoms in a magneto-optical trap (MOT). The qualities of the electron source will have direct effects on the brightness, coherence, and line width of the free electron laser. A high quality ultra-cold electron source is obtained by carefully optimizing the extraction electrode structure, the acceleration and focusing system as well as the MOT. Through parameter optimization, a coherent electron source with a temperature lower than 10 K is obtained. Details of the optimization and the characteristics of the coherent electron source are reported in this paper. 		 
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-FEL2019-WEP059  
About • paper received ※ 24 August 2019       paper accepted ※ 10 September 2019       issue date ※ 05 November 2019  
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WEP103 A Plasma Attenuator for Soft X-Rays in LCLS-II plasma, electron, FEL, controls 553
 
  • A.S. Fisher, A.L. Benwell, Y. Feng, B.T. Jacobson
    SLAC, Menlo Park, California, USA
  
  Attenuation of X-ray FEL beams is often required to avoid damaging optics and detectors during alignment, and to study fluence-dependent effects. Soft X-rays are commonly attenuated by photoabsorption in a gas such as argon. However, absorbing a mJ pulse along a meter creates a pressure wave that drives gas away from the X-ray propagation axis, until equilibrium recovers in ~1 ms. This timescale matched the 120-Hz pulse spacing of LCLS, but at the high repetition rate (up to 1 MHz) and power (up to 200 W) of LCLS-II, the attenuation of subsequent pulses is reduced. Simulations demonstrate hysteresis and erratic attenuation from gas-density depletion. Instead, we propose to replace the gas column with an argon plasma in a TM010 RF cavity. The density profile then is largely set by the RF mode. X-ray absorption becomes a perturbation compared to the energy in the plasma. An LCLS-II solid-state RF amplifier, generating up to 4 kW at 1.3 GHz, can provide the drive, and the FPGA-based low-level RF controller can be programmed to track tuning with plasma density. Several diagnostics are planned to monitor plasma properties over a fill-pressure range of 10 to 1000 Pa.  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-FEL2019-WEP103  
About • paper received ※ 16 August 2019       paper accepted ※ 28 August 2019       issue date ※ 05 November 2019  
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THB04 Longitudinal Phase Space Study on Injector Beam of High Repetition Rate X-Ray FEL linac, electron, bunching, laser 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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THP007 Frequency-Detuning Dependent Transient Coaxial RF Coupler Kick gun, focusing, simulation, electron 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 linac, electron, SRF, operation 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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THP018 Transverse Deflecting Structure Dynamics for Time-Resolved Machine Studies of Shine electron, FEL, free-electron-laser, laser 632
 
  • J.W. Yan, H.X. Deng, B. Liu, D. Wang
    SINAP, Shanghai, People’s Republic of China
  • H.X. Deng, B. Liu, D. Wang
    SARI-CAS, Pudong, Shanghai, People’s Republic of China
  
  Funding: National Natural Science Foundation of China (11775293), the National Key Research and Development Program of China (2016YFA0401900) and Ten Thousand Talent Program.
The transverse deflecting structure (TDS) has been widely used in modern free electron laser facilities for the longitudinal phase space diagnostics of electron beams. As the first hard x-ray free electron laser in China, the SHINE is designed to deliver photons with a repetition rate up to 1 MHz. In this paper, we present the beam dynamics study of the X-band TDS behind the undulator of SHINE. In order to prevent the screen from being damaged by electron bunches with a high repetition rate, the phase of the transverse deflecting cavity is designed to deviate from zero, and only those electron bunches that are kicked by the transverse deflecting cavity are sent to the screen. In addition, the evolutionary algorithm is introduced to optimize the lattice of the TDS line to reach the highest possible resolution. 		 
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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THP054 Nanosecond Pulse Enhancement in Narrow Linewidth Cavity for Steady-State Microbunching laser, simulation, optics, impedance 697
 
  • Q.H. Zhou
    Southwest University of Science and Technology, Mianyang, Sichuan, People’s Republic of China
  
  Funding: The National Natural Science Foundation of China under Grant No.11875227.
In steady-state microbunching (SSMB), nanosecond laser pulse with megawatt average power is required. We build up a theoretic model to enhance such pulse in a narrow linewidth (e.g. kHz level) cavity for this demand, which shows that a mode-locked mechanism in frequency domain should be considered. Simulations indicate that such pulse can be enhanced sufficiently under this condition. And we also propose some experimental schematics to realize it. 		 
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-FEL2019-THP054  
About • paper received ※ 25 August 2019       paper accepted ※ 22 October 2019       issue date ※ 05 November 2019  
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