MC2: Photon Sources and Electron Accelerators
A06: Free Electron Lasers
Paper Title Page
TUIYSP1
 Science Highlights From Hard X-Ray FELs  
 
  • T. Tschentscher
    EuXFEL, Hamburg, Germany
  
  X-ray Free-Electron Lasers (XFELs), using high energy electron accelerators, are in operation since little more than a decade and have become a highly successful platform for scientific applications. From physics via chemistry and life-science to materials and planetary sciences XFELs are used to study atomic and electronic structure with angstrom and femtosecond resolution. The presentation will show examples of high impact research at the various facilities. A relation between the special features these XFEL facilities provide and the science enabled by them will be discussed. In the last part emphasis will be given to on-going and future developments adding capability to the XFEL facilities with the goal to widen the scientific applications and thus societal impact.  
slides icon Slides TUIYSP1 [28.758 MB]  
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TUIYSP2
 Self-Amplification of Coherent Energy Modulation in Seeded Free-Electron Lasers  
 
  • H.X. Deng
    SINAP, Shanghai, People’s Republic of China
  
  We report a novel self-amplification method for enhancing laser-induced energy modulation, thereby significantly reducing requirements on the external laser system in a seeded free-electron laser (FEL). Driven by this scheme, we experimentally realized high harmonic generation in a seeded FEL using an unprecedentedly small external laser-induced energy modulation. An electron beam with the laser-induced energy modulation as small as 1.8 times the slice energy spread has been used for lasing at the seventh harmonic of 266-nm seed laser in a single-stage high-gain harmonic generation (HGHG) setup and the 30th harmonic of the seed laser in a two-stage HGHG setup. The results mark a major step towards a high-repetition-rate, fully coherent X-ray FEL.  
slides icon Slides TUIYSP2 [3.544 MB]  
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TUIYSP3
 Research and Development Towards Cavity-Based X-ray Free-Electron Lasers  
 
  • G. Marcus
    SLAC, Menlo Park, California, USA
  
  Cavity-based X-ray free-electron laser concepts such as the regenerative amplifier FELs (RAFEL) and the X-ray FEL oscillator (XFELO) offer a promising path towards enhancing the brightness of XFELs by up to two orders of magnitude. We will present the ongoing research effort at the SLAC National Accelerator Laboratory and Argonne National Laboratory to demonstrate these concepts. We will discuss recent experimental tests of X-ray cavity performance and present plans for a proof-of-principle experiment at LCLS, as well as ideas for future cavity-based XFEL facilities.  
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TUPOPT005 Status of the Superconducting Soft X-Ray Free-Electron Laser User Facility FLASH 1006
 
  • M. Vogt, C. Gerth, K. Honkavaara, M. Kuhlmann, J. Rönsch-Schulenburg, L. Schaper, S. Schreiber, R. Treusch, J. Zemella
    DESY, Hamburg, Germany
  
  The XUV and soft X-ray free-electron laser FLASH at DESY is capable of operating two undulator beamlines simultaneously with up to several thousand bunches per second. It is driven by a normal conducting RF photo-cathode gun and a superconducting L-band linac. FLASH is currently undergoing a substantial refurbishment and upgrade program (FLASH2020+). The first 9-months installation shutdown started in November 2021. Here we report on the operation in 2021 and present main upgrades during the ongoing shutdown.  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2022-TUPOPT005  
About • Received ※ 07 June 2022 — Revised ※ 13 June 2022 — Accepted ※ 15 June 2022 — Issue date ※ 17 June 2022
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TUPOPT006 The New FLASH1 Beamline for the FLASH2020+ Project 1010
 
  • M. Vogt, J. Zemella
    DESY, Hamburg, Germany
  
  The 2nd stage of the FLASH2020+ project will be an upgrade of the FLASH1 beamline, downstream of the injector/linac section FLAH0 which is currently being upgraded. The currently existing beamline drives the original planar fixed gap SASE undulators from the TTF-2 setup, a THz undulator that uses the spent electron beam and deflects the e-beam into a dump beamline capable of safely dumping several thousand bunches per second. The updated beamline has been designed for EEHG seeding with 2 modulators, 3 chicanes, and a helical Apple-III undulator beamline as seeding radiator, followed by a transverse deflecting (S-band) structure for longitudinal diagnostics. The separation of the electron beam from the FEL beam will be moved upstream w.r.t. the old design to create more space for the photon diagnostics and will be achieved by a 5 deg double-bend-almost-achromat. To allow enable high power THz radiation output from a moderately compressed seeding beam, a post compressor will be installed. The capability of dumping the the long bunch trains safely may and will not be compromised by the design. This article describes the conceptional and some technical and details of the beamline.  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2022-TUPOPT006  
About • Received ※ 07 June 2022 — Accepted ※ 13 June 2022 — Issue date ※ 23 June 2022  
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TUPOPT008 An Overview of the T20 Beamline for the LUXE Experiment at the European XFEL 1014
 
  • S.D. Walker, N. Golubeva
    DESY, Hamburg, Germany
  
  The Laser Und XFEL Experiment (LUXE) at the EUXFEL aims to explore hitherto unprobed regions of quantum electrodynamics characterised by both high-energy and high-intensity. This will be accomplished by leveraging the electron beam provided by the EUXFEL and an intensely-focussed laser to study electron-photon and photon-photon interactions. The LUXE experiment will be placed in the empty XTD20 tunnel and to this end a new beamline, T20, will need to be installed to deliver one bunch per bunch train to LUXE. The T20 beamline feature a total bend angle of 6.7 degrees, which combined with the very short bunches provided by the EUXFEL raises concerns regarding the deleterious impact of of coherent synchrotron radiation (CSR) on the bunch emittances. As the LUXE experiment has specific beam size requirements at its IP, these effects and the limits on the focus must be characterised. In this paper the T20 beamline design and its final focus are outlined. Furthermore, the impact of collective effects on the beam quality at the LUXE IP are discussed, and finally a means to mitigate the impact of these effects and improve the beam quality at the LUXE IP is shown.  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2022-TUPOPT008  
About • Received ※ 13 June 2022 — Revised ※ 14 June 2022 — Accepted ※ 19 June 2022 — Issue date ※ 10 July 2022
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TUPOPT010 Virtual Commissioning of the European XFEL for Advanced User Experiments at Photon Energies Beyond 25 keV Using Low-Emittance Electron Beams 1018
 
  • Y. Chen, F. Brinker, W. Decking, M. Scholz, L. Winkelmann, Z.H. Zhu
    DESY, Hamburg, Germany
  
  Funding: The authors acknowledge support from Deutsches Elektronen-Synchrotron DESY (Hamburg, Germany), a member of the Helmholtz Association HGF and European XFEL GmbH (Schenefeld, Germany).
Growing interests in ultra-hard X-rays are pushing forward the frontier of commissioning the European X-ray Free-Electron Laser (XFEL) for routine operation towards the sub-ångström regime, where a photon energy of 25 keV (0.5 ångström) is desired. Such X-rays allow for larger penetration depths and enable the investigation of materials in highly absorbing environments. Delivering the requested X-rays to user experiments is of crucial importance for the XFEL development. Unique capabilities of the European XFEL are formed by combining a high energy linac and the long variable-gap undulator systems for generating intense X-rays at 25 keV and pushing the limit even further to 30 keV. However, the FEL performance relies on achievable electron bunch qualities. Low-emittance electron bunch production, and the associated start-to-end modelling of beam physics thus becomes a prerequisite to dig into the XFEL potentials. Here, we present the obtained results from a virtual commissioning of the XFEL for the user experiments at 25 keV and beyond, including the optimized electron bunch qualities at variable accelerating cathode gradients and lasing studies under different conditions.
*Appl. Sci. 11(22), 10768 (2021)
**Phys. Rev. Accel. Beams 23, 044201(2020)
***NIM A 995, 11 165111 (2021) 		 
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2022-TUPOPT010  
About • Received ※ 19 May 2022 — Revised ※ 11 June 2022 — Accepted ※ 13 June 2022 — Issue date ※ 08 July 2022
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TUPOPT011 Start To End Simulation Study For Oscillator-Amplifier Free-Electron Laser 1022
 
  • H. Sun, Z.H. Zhu
    SINAP, Shanghai, People’s Republic of China
  • C. Feng, B. Liu
    SARI-CAS, Pudong, Shanghai, People’s Republic of China
  • Z.H. Zhu
    DESY, Hamburg, Germany
  
  External seeding techniques like high-gain harmonic generation (HGHG) and echo-enabled harmonic generation (EEHG) have been proposed and proven to be able to generate fully coherent radiation in the EUV and X-ray range. A big challenge is to combine the advantages of seeding schemes with high repetition rates. Recently, for seeding at a high repetition rate, an optical resonator scheme has been introduced to recirculate the radiation in the modulator to seed the high repetition rate electron bunches. Earlier studies have shown that a resonator-like modulator combined with an amplifier in high gain harmonic generation (HGHG) configuration can be used to generate radiation whose wavelength can reach the water window region. This scheme overcomes the limitation of requiring high repetition rate seed laser systems. In this contribution, we present start-to-end simulation results of a seeded oscillator-amplifier FEL scheme.  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2022-TUPOPT011  
About • Received ※ 07 June 2022 — Revised ※ 11 June 2022 — Accepted ※ 11 June 2022 — Issue date ※ 16 June 2022
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TUPOPT013 Twin Delayed Deep Deterministic Policy Gradient for Free-electron Laser Online Optimization 1025
 
  • M. Cai, C. Feng, L. Tu, Z.T. Zhao, Z.H. Zhu
    SINAP, Shanghai, People’s Republic of China
  • C. Feng, K.Q. Zhang, Z.T. Zhao
    SSRF, Shanghai, People’s Republic of China
  • D. Gu
    SARI-CAS, Pudong, Shanghai, People’s Republic of China
  
  X-ray free-electron lasers (FEL) have contributed to many frontier applications of nanoscale science which benefit from its extraordinary properties. During FEL commissioning, the beam status optimization especially orbit correction is particularly significant for FEL amplification. For example, the deviation between beam orbit and the magnetic center of undulator can affect the interaction between the electron beam and the FEL pulse. Usually, FEL commissioning requires a lot of effort for multi-dimensional parameters optimization in a time-varying system. Therefore, advanced algorithms are needed to facilitate the commissioning procedure. In this paper, we propose an online method to optimize the FEL power and transverse coherence by using a twin delayed deep deterministic policy gradient (TD3) algorithm. The algorithm exhibits more stable learning convergence and improves learning performance because the overestimation bias of policy gradient methods is suppressed.  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2022-TUPOPT013  
About • Received ※ 17 May 2022 — Revised ※ 14 June 2022 — Accepted ※ 15 June 2022 — Issue date ※ 22 June 2022
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TUPOPT014 The Status of the SASE3 Variable Polarization Project at the European XFEL 1029
 
  • S. Karabekyan, S. Abeghyan, M. Bagha-Shanjani, S. Casalbuoni, U. Englisch, W. Freund, G. Geloni, J. Grünert, S. Hauf, C. Holz, D. La Civita, J. Laksman, D. Mamchyk, M.P. Planas, F. Preisskorn, S. Serkez, H. Sinn, M. Wuenschel, M. Yakopov, C. Youngman
    EuXFEL, Schenefeld, Germany
  • P. Altmann, A. Block, W. Decking, L. Fröhlich, O. Hensler, T. Ladwig, D. Lenz, D. Lipka, R. Mattusch, N. Mildner, E. Negodin, J. Prenting, F. Saretzki, M. Schlösser, F. Schmidt-Föhre, E. Schneidmiller, M. Scholz, D. Thoden, T. Wamsat, T. Wilksen, T. Wohlenberg, M.V. Yurkov
    DESY, Hamburg, Germany
  • J. Bahrdt
    HZB, Berlin, Germany
  • M. Brügger, M. Calvi, S. Danner, R. Ganter, L. Huber, A. Keller, C. Kittel, X. Liang, S. Reiche, M.S. Schmidt, T. Schmidt, K. Zhang
    PSI, Villigen PSI, Switzerland
  • D.E. Kim
    PAL, Pohang, Republic of Korea
  • Y. Li
    IHEP, People’s Republic of China
  
  The undulator systems at the European XFEL consist of two hard X-ray systems, SASE1 and SASE2, and one soft X-ray system, SASE3. All three systems are equipped with planar undulators using permanent neodymium magnets. These systems allow the generation of linearly polarized radiation in the horizontal plane. In order to generate variable polarization radiation in the soft X-ray range, an afterburner is currently being implemented behind the SASE3 planar undulator system. It consists of four APPLE-X helical undulators. The project, called SASE 3 Variable Polarization, is close to being put into operation. All four helical undulators have been installed in the tunnel during the 2021-2022 winter shutdown. This paper describes the status of the project and the steps toward its commissioning. It also presents lessons learned during the implementation of the project.  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2022-TUPOPT014  
About • Received ※ 02 June 2022 — Revised ※ 12 June 2022 — Accepted ※ 13 June 2022 — Issue date ※ 05 July 2022
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TUPOPT016 Status of the THz@PITZ Project - The Proof-of-Principle Experiment on a THz SASE FEL at the PITZ Facility 1033
 
  • T. Weilbach, P. Boonpornprasert, G.Z. Georgiev, G. Koss, M. Krasilnikov, X.-K. Li, A. Lueangaramwong, F. Mueller, A. Oppelt, S. Philipp, F. Stephan
    DESY Zeuthen, Zeuthen, Germany
  
  Funding: This work was supported by the European XFEL research and development program.
In order to allow THz pump/X-ray probe experiments at full bunch repetition rate for users at the European XFEL, the Photo Injector Test Facility at DESYin Zeuthen (PITZ) is building a prototype of an accelerator-based THz source. The goal is to generate THz SASE FEL radiation with a mJ energy level per bunch using an undulator driven by the electron beam from PITZ. Therefore, the existing PITZ beam line is extended into a tunnel annex downstream of the existing accelerator tunnel. The final design of the beam line extension consists of a bunch compressor, a collimation system and a beam dump in the PITZ tunnel. In the tunnel annex one LCLS-I undulator is installed for the production of the THz radiation with a quadrupole triplet in front of it for matching the beam parameters for the FEL process. Behind the undulator two screen stations couple out the THz radiation, for measurements of bunch compression, pulse energy or spatial distribution. A dipole separates the electron from the THz beam and a quadrupole doublet transports the electron beam to the beam dump. The installation progress will be presented. 		 
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2022-TUPOPT016  
About • Received ※ 07 June 2022 — Revised ※ 15 June 2022 — Accepted ※ 16 June 2022 — Issue date ※ 25 June 2022
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TUPOPT017 Start-to-end Simulations for Bunch Compressor and THz SASE FEL at PITZ 1037
 
  • A. Lueangaramwong, P. Boonpornprasert, M. Krasilnikov, X.-K. Li, F. Stephan
    DESY Zeuthen, Zeuthen, Germany
  
  The magnetic bunch compressor was designed as part of a THz accelerator source being developed at the Photo Injector Test facility at DESY in Zeuthen (PITZ) as a prototype for pump-probe experiments at the European XFEL. As an electron bunch is compressed to achieve higher bunch currents for the THz source, the beam dynamics in the bunch compressor was studied by numerical simulations. A start-to-end simulation optimizer including coherent synchrotron radiation (CSR) effects has been developed by combining the use of ASTRA, OCELOT, and GENESIS to support the design of the THz source prototype. In this paper we present simulation results to explore the possibility of improving the performance of the THz FEL at PITZ by using the developed bunch compressor.  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2022-TUPOPT017  
About • Received ※ 18 May 2022 — Revised ※ 11 June 2022 — Accepted ※ 13 June 2022 — Issue date ※ 13 June 2022
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TUPOPT018 Fermi 2.0 Future Upgrade Strategy 1041
 
  • L. Giannessi, E. Allaria, L. Badano, F. Bencivenga, C. Callegari, F. Capotondi, D. Castronovo, P. Cinquegrana, M. Coreno, M.B. Danailov, G. De Ninno, P. Delgiusto, A.A. Demidovich, S. Di Mitri, B. Diviacco, W.M. Fawley, M. Ferianis, G. Gaio, F. Gelmetti, G. Kurdi, M. Lonza, M. Malvestuto, M. Manfredda, C. Masciovecchio, I. Nikolov, G. Penco, K.C. Prince, E. Principi, P. Rebernik Ribič, C. Scafuri, N. Shafqat, P. Sigalotti, A. Simoncig, F. Sottocorona, S. Spampinati, C. Spezzani, L. Sturari, M. Trovò, M. Veronese, R. Visintini, M. Zangrando
    Elettra-Sincrotrone Trieste S.C.p.A., Basovizza, Italy
  • M. Coreno
    CNR-ISM, Trieste, Italy
  • G. Penn
    LBNL, Berkeley, California, USA
  • G. Perosa
    Università degli Studi di Trieste, Trieste, Italy
  • T. Tanaka
    RIKEN SPring-8 Center, Hyogo, Japan
  
  FERMI is studying a series of developments to keep the facility in a world-leading position on the base of the requests coming from the user community, the Scientific Advisory Council and the Machine Advisory Committee. The ultimate goal of the development plan consists in doubling the photon energy range and reducing the pulse duration below the characteristic lifetime of the atomic core levels located in the energy range of the source. One of the most promising approaches is the echo-enabled harmonic generation (EEHG) scheme, relying on two external lasers to precisely control the spectro-temporal properties of the FEL pulse. The implementation of EEHG in the double-stage harmonic cascade presently in use on FEL-2, would allow harmonics as high as 120 enabling to generate coherent pulses down to 2 nm starting from UV lasers. An upgrade of FERMI aimed at reaching the oxygen K-edge requires a profound modification of the FEL configurations and of the main components of the machine, including the linac and the undulator lines. The main aspects of the upgrade strategy will be discussed in this presentation.  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2022-TUPOPT018  
About • Received ※ 08 June 2022 — Revised ※ 14 June 2022 — Accepted ※ 15 June 2022 — Issue date ※ 07 July 2022
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TUPOPT019 FERMI FEL-1 Upgrade to EEHG 1044
 
  • C. Spezzani, E. Allaria, L. Badano, D. Castronovo, P. Cinquegrana, M.B. Danailov, R. De Monte, G. De Ninno, P. Delgiusto, A.A. Demidovich, S. Di Mitri, B. Diviacco, M. Ferianis, G. Gaio, F. Gelmetti, L. Giannessi, G. Kurdi, M. Lonza, C. Masciovecchio, I. Nikolov, G. Penco, P. Rebernik Ribič, C. Scafuri, N. Shafqat, P. Sigalotti, F. Sottocorona, S. Spampinati, L. Sturari, M. Trovò, M. Veronese, R. Visintini
    Elettra-Sincrotrone Trieste S.C.p.A., Basovizza, Italy
  • G. Perosa
    Università degli Studi di Trieste, Trieste, Italy
  
  The Fermi free-electron laser (FEL) facility is operating since 2010 providing the user community with ultrashort pulses in the VUV- XUV range. Using the High Gain Harmonic Generation (HGHG) setup, nearly transform-limited pulses with gigawatt peak power are made available. Furthermore, several multicolor and coherent control schemes are possible and highly required from the user community. To meet the request of extending the spectral range over the whole water window, an upgrade strategy of the FERMI facility has recently initiated. During the first phase of the upgrade, the single cascade FEL-1 will be adapted to operate either in Echo Enabled Harmonic Generation (EEHG) or in HGHG. Required modifications can be achieved with limited impact on FERMI operations and will improve FEL-1’s spectral range, spectral quality and flexibility. The second phase includes modification of the FEL-2 setup and will benefit from the experience gained with phase 1. The two phases will proceed in parallel to the linac upgrade aiming at extending the beam energy to 1.8 GeV. We report here details on the upgrade of the FEL-1 foreseen to provide light to users in the new configuration by spring 2023.  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2022-TUPOPT019  
About • Received ※ 07 June 2022 — Revised ※ 14 June 2022 — Accepted ※ 21 June 2022 — Issue date ※ 29 June 2022
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TUPOPT023 Undulator Tapering Studies of an Echo-Enabled Harmonic Generation Based Free-Electron Laser 1047
SUSPMF010   use link to see paper's listing under its alternate paper code  
 
  • F. Pannek, W. Hillert
    University of Hamburg, Institut für Experimentalphysik, Hamburg, Germany
  • S. Ackermann, E. Ferrari, L. Schaper
    DESY, Hamburg, Germany
  
  The free-electron laser (FEL) user facility FLASH at DESY is currently undergoing an upgrade which involves the transformation of one of its beamlines to allow for external seeding via so-called Echo-Enabled Harmonic Generation (EEHG). With this seeding technique it will be possible to provide stable, longitudinal coherent and intense radiation in the XUV and soft X-ray regime at high repetition rate. To ensure an efficient FEL amplification process, sustainable energy exchange between the electrons and the electromagnetic field in the undulator is mandatory. Adequate adjustment of the undulator strength along the beamline allows to compensate for electron energy loss and to preserve the resonance condition. The impact of this undulator tapering on the temporal and spectral characteristics on the EEHG FEL radiation at 4 nm is investigated by means of numerical simulations performed with the FEL code GENESIS 1.3, version 4. Different tapering methods are examined and it is shown that specific tapering of the undulator strength allows to exceed the FEL saturation power while maintaining a clear temporal and spectral shape of the FEL pulse.  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2022-TUPOPT023  
About • Received ※ 08 June 2022 — Revised ※ 15 June 2022 — Accepted ※ 16 June 2022 — Issue date ※ 27 June 2022
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TUPOPT025 Concept of Electron Beam Diagnostics for PolFEL 1055
 
  • A.I. Wawrzyniak, G.W. Kowalski, A.M. Marendziak, R. Panaś
    NSRC SOLARIS, Kraków, Poland
  • A. Curcio
    CLPU, Villamayor, Spain
  • P.J. Czuma, M. Krakówiak, P. Krawczyk, R. Kwiatkowski, S. Mianowski, R. Nietubyc, M. Staszczak, J. Szewiński, M. Terka, M. Wójtowicz
    NCBJ, Świerk/Otwock, Poland
  • K. Łasocha
    Jagiellonian University, Kraków, Poland
  
  PolFEL - Polish Free Electron Laser will be driven by a continuous wave superconducting accelerator consist-ing of low emittance superconducting RF electron gun, four accelerating cryomodules, bunch compressors, beam optics components and diagnostic elements. The acceler-ator will split in three branches leading to undulators pro-ducing VUV, IR and THz radiation, respectively. Two accelerating cryomodules will be installed before a dogleg directing electron bunches towards IR and THz branches. Additional two cryomodules will be placed in the VUV branch accelerating electron bunches up to 185 MeV at 50 kHz repetition rate. Moreover, the electron beam after passing the VUV undulator will be directed to the Inverse Compton Scattering process for high energy photons experiments in a dedicated station. In order to measure and optimise the electron beam parameters along the entire accelerator the main diagnostics components like BPMs, charge monitors, YAG screens, coherent diffrac-tion radiation (CDR) monitors and beam loss monitors are foreseen. Within this presentation the concept of the electron beam diagnostics will be discussed.  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2022-TUPOPT025  
About • Received ※ 09 June 2022 — Revised ※ 10 June 2022 — Accepted ※ 16 June 2022 — Issue date ※ 27 June 2022
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TUPOPT027 Numerical Simulation of a Superradiant THz Source at the PITZ Facility 1063
 
  • N. Chaisueb, S. Rimjaem
    Chiang Mai University, Chiang Mai, Thailand
  • P. Boonpornprasert, M. Krasilnikov, X.-K. Li, A. Lueangaramwong
    DESY Zeuthen, Zeuthen, Germany
  • S. Rimjaem
    ThEP Center, Commission on Higher Education, Bangkok, Thailand
  
  An accelerator-based THz source is under development at the Photo Injector Test Facility at DESY in Zeuthen (PITZ). The facility can produce high brightness electron beams with high charge and small emittance. Currently, a study on development of a tunable high-power THz SASE FEL for supporting THz-pump, X-ray-probe experiments at the European XFEL is underway. An LCLS-I undulator, a magnetic chicane bunch compressor, and THz pulse diagnostics have been installed downstream the previously existing setup of the PITZ beamline. Additional to the SASE FEL, a possibility to generate superradiant THz undulator radiation from short electron bunches is under investigation, which is the focus in this study. Numerical simulations of the superradiant THz radiation by using sub-picosecond electron bunches with energy of 6 - 22 MeV and bunch charge up to 2 nC produced from the PITZ accelerator are performed. The results show that the radiation with a spectral range of 0.5 to 9 THz and a pulse energy in the order of sub-uJ can be obtained. The results from this study can be used as a benchmark for the future development.  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2022-TUPOPT027  
About • Received ※ 08 June 2022 — Revised ※ 13 June 2022 — Accepted ※ 16 June 2022 — Issue date ※ 07 July 2022
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TUPOPT028 THz Undulator Radiation Based on Super-Radiant Technique at Chiang Mai University 1067
 
  • E. Kongmon
    IST, Chiang Mai, Thailand
  • N. Chaisueb, S. Rimjaem
    Chiang Mai University, Chiang Mai, Thailand
  • S. Rimjaem
    ThEP Center, Commission on Higher Education, Bangkok, Thailand
  
  A linear accelerator system at the PBP-CMU Electron Linac Laboratory is used as an electron source for generating coherent THz radiation and MIR-FEL. To achieve high power THz radiation, the super-radiant technique using pre-bunched electrons and undulator magnet is utilized. In this study, we investigate the generation of such radiation with comparable properties as the FEL. The beamline composes of a 180-degree magnetic bunch compressor, a 2 m-electromagnet undulator, quadrupole magnets and diagnostic devices. This work includes the undulator design and investigation on properties of electron beam and THz radiation. Based-on the results of beam dynamic study, the optimized electron beams have an energy in a range of 10-16 MeV, a bunch charge of 100 pC, and a bunch length of 300 fs. The radiation with frequency covering from 0.5 to 3 THz yields a peak power of 5.21 MW at 1.15 THz. This information was used as an initial parameter for undulator design by using the CST-EM Studio software. It has 19.5 periods with a period length of 100 mm. The design results show that the maximum magnetic field is 0.2317 T. The results of this study are used as the guideline for construction of the undulator and the THz-FEL beamline.  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2022-TUPOPT028  
About • Received ※ 08 June 2022 — Revised ※ 11 June 2022 — Accepted ※ 13 June 2022 — Issue date ※ 27 June 2022
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TUPOPT029 Infrared Free-Electron Laser Project in Thailand 1070
 
  • S. Rimjaem, N. Chaisueb, P. Kitisri, K. Kongmali, E. Kongmon, P. Nanthanasit, S. Pakluea, J. Saisut, S. Sukara, K. Techakaew, C. Thongbai
    Chiang Mai University, Chiang Mai, Thailand
  • P. Apiwattanakul, P. Jaikaew, W. Jaikla, N. Kangrang
    Chiang Mai University, PBP Research Facility, Chiang Mai, Thailand
  • M. Jitvisate
    Suranaree University of Technology, Nakhon Ratchasima, Thailand
  • M.W. Rhodes
    ThEP Center, Commission on Higher Education, Bangkok, Thailand
  
  The infrared free-electron laser (IR FEL) project is established at Chiang Mai University in Thailand with the aim to provide experimental stations for users utilizing accelerator-based terahertz (THz) and mid-infrared (MIR) radiation. Main components of the system include a thermionic RF gun, an alpha magnet as a bunch compressor and energy filter, a standing-wave RF linac, a THz transition radiation (THz-TR) station, two magnetic bunch compressors and beamlines for MIR/THz FEL. The system commissioning is ongoing to produce the beams with proper properties. Simulation results suggest that the oscillator MIR-FEL with wavelengths of 9.5-16.6 um and pulse energies of 0.15-0.4 uJ can be produced from 60-pC electron bunches with energy of 20-25 MeV. The super-radiant THz-FEL with frequencies of 1-3 THz and 700 kW peak power can be produced from 10-16 MeV electron bunches with a charge of 50 pC and a length of 200-300 fs. Furthermore, the THz-TR with a spectral range of 0.3-2.5 THz and a pulse power of up to 1.5 MW can be obtained. The MIR/THz FEL will be used as high-brightness light source for pump-probe experiments, while the coherent THz-TR will be used in time-domain spectroscopy.  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2022-TUPOPT029  
About • Received ※ 08 June 2022 — Revised ※ 12 June 2022 — Accepted ※ 13 June 2022 — Issue date ※ 16 June 2022
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TUPOPT030 Design and Simulation of the MIR-FEL Generation System at Chiang Mai University 1074
SUSPMF012   use link to see paper's listing under its alternate paper code  
 
  • S. Sukara, K. Kongmali, S. Rimjaem
    Chiang Mai University, Chiang Mai, Thailand
  • H. Ohgaki
    Kyoto University, Kyoto, Japan
  
  At the PBP-CMU Electron Linac Laboratory, the system to generate MIR-FEL using the electron linac has been developed. In this contribution, the design and simulation results of the MIR-FEL generation system are presented. The system is designed as the oscillator-FEL type consisting of two mirrors and a 1.6-m permanent planar undulator. The middle of the undulator is determined as the laser beam waist position. Both two mirrors are the concave gold-coated copper mirrors placing upstream and downstream the optical cavity, which has a total length of 5.41 m. The FEL is designed to coupling out at a hole with diameter of 2 mm on the upstream mirror. The optical cavity is optimized to obtain high FEL gain and high FEL power using GENESIS 1.3 simulation code. The electron beam with energy of 25 MeV is used in the consideration. As a result, the MIR-FEL with central wavelength of 13.01 ’m is obtained. The optimum upstream and downstream mirror curvatures are 3.091 m and 2.612 m, respectively, which give the Rayleigh length of 0.631 m. This optical cavity yields the power coupling ratio of 1:1000 and the FEL gain of up to 40%. The extracted MIR-FEL peak power in 100 kW scale is obtained at the coupling hole. The construction of the practical MIR-FEL system is conducted based on the results from this study.  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2022-TUPOPT030  
About • Received ※ 08 June 2022 — Revised ※ 15 June 2022 — Accepted ※ 16 June 2022 — Issue date ※ 01 July 2022
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TUPOPT032 Simulating Beam Transport with Permanent Magnet Chicane for THz Fel 1077
SUSPMF013   use link to see paper's listing under its alternate paper code  
 
  • A.C. Fisher, M.P. Lenz, P. Musumeci, A. Ody, Y. Park
    UCLA, Los Angeles, USA
  • R.B. Agustsson, T.J. Hodgetts, A.Y. Murokh
    RadiaBeam, Santa Monica, California, USA
  
  Funding: This work was supported by NSF grant PHY-1734215 and DOE grant No. DE-SC0009914 and DE-SC0021190. The undulator construction has been carried out under SBIR/STTR DE-SC0017102 and DE-SC0018559.
Free electron lasers are an attractive option for high average and peak power radiation in the THz gap, a region of the electromagnetic spectrum where radiation sources are scarce, as the required beam and undulator parameters are readily achievable with current technology. However, slippage effects require the FEL to be driven with relatively long and low current electron bunches, limiting amplification gain and output power. Previous work demonstrated that a waveguide could be used to match the radiation and e-beam velocities in a meter-long strongly-tapered helical undulator, resulting in 10\% energy extraction from an ultrashort 200 pC, 5.5 MeV electron beam. We present simulations for a follow-up experiment targeting higher frequencies with improvements to the e-beam transport including a permanent magnet chicane for strong beam compression. FEL simulations show >20\% extraction efficiency from a 125 pC, 7.4 MeV electron beam at 0.32 THz. 		 
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2022-TUPOPT032  
About • Received ※ 07 June 2022 — Revised ※ 12 June 2022 — Accepted ※ 13 June 2022 — Issue date ※ 28 June 2022
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TUPOPT034 Modelling of X-Ray Volume Excitation of the XLO Gain Medium Using Flash 1081
 
  • P. Manwani, N. Majernik, B. Naranjo, J.B. Rosenzweig
    UCLA, Los Angeles, California, USA
  • E.C. Galtier, A. Halavanau, C. Pellegrini
    SLAC, Menlo Park, California, USA
  
  Funding: This work was performed with the support of the US Department of Energy under Contract No. DE-AC02-76SF00515 and DESC0009914.
Plasma dynamics and crater formation of laser excited volumes in solids is a complex process due to thermalization, shockwave formation, varying absorption mechanisms, and a wide range of relevant physics timescales. The properties and interaction of such laser-matter systems can be modeled using an equation of state and opacity based multi-temperature treatment of plasma using a radiation hydrodynamics code. Here, we use FLASH, an adaptive mesh radiation-hydrodynamics code, to simulate the plasma expansion following after the initial energy deposition and thermalization of the column, to benchmark the results of experiments undertaken at UCLA on optical laser ablation. These computational results help develop a quantitative understanding of the material excitation process and enable the optimization of the gain medium delivery system for the x-ray laser oscillator project *.
* Halavanau, Aliaksei, et al. "Population Inversion X-Ray Laser Oscillator." Proceedings of the National Academy of Sciences, vol. 117, no. 27, 2020, pp. 15511-15516. 		 
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2022-TUPOPT034  
About • Received ※ 08 June 2022 — Revised ※ 16 June 2022 — Accepted ※ 18 June 2022 — Issue date ※ 24 June 2022
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TUPOPT036 Two and Multiple Bunches with the LCLS Copper Linac 1089
 
  • F.-J. Decker, W.S. Colocho, A. Halavanau, A.A. Lutman, J.P. MacArthur, G. Marcus, R.A. Margraf, J.C. Sheppard, J.J. Turner, S. Vetter
    SLAC, Menlo Park, California, USA
  
  Two, four, and even eight bunches were accelerated through the copper linac. Two and four bunches were delivered successfully to photon experiments in both the hard (HXR) and soft (SXR) LCLS x-ray lines. In this paper we will concentrate on the more challenging issues, such as: the BPM deconvolution for both bunches, RF kicks at longer separations, tuning challenges, bridging the communications gap between the photon and electron side, the lower bunch charges for the eight bunch case, and rapid timing scans over several ns. We will describe some of the developed solutions and plans for the rest.  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2022-TUPOPT036  
About • Received ※ 07 June 2022 — Revised ※ 12 June 2022 — Accepted ※ 13 June 2022 — Issue date ※ 28 June 2022
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TUPOPT037 LCLS Multi-Bunch Improvement Plan: First Results 1092
 
  • A. Halavanau, A.L. Benwell, T.G. Beukers, L.B. Borzenets, F.-J. Decker, J. Hugyik, A. Ibrahimov, E.N. Jongewaard, A.K. Krasnykh, A.L. Le, K. Luchini, A.A. Lutman, A. Marinelli, M. Petree, A. Romero, A.V. Sy
    SLAC, Menlo Park, California, USA
  
  LCLS copper linac primarily operates in a single bunch mode with a repetition rate of 120 Hz. Presently, several in-house projects and LCLS user experiments require double- and multi-pulse trains of X-rays, with inter-pulse delay spanning between 0.35 and 220 ns. We discuss beam control improvements to the copper linac using ultra-fast stripline kicker, as well as additional photon diagnostics. We especially focus on a case of double-pulse mode, with 218 ns separation.  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2022-TUPOPT037  
About • Received ※ 12 June 2022 — Revised ※ 13 June 2022 — Accepted ※ 17 June 2022 — Issue date ※ 10 July 2022
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TUPOPT038 FAST-GREENS: A High Efficiency Free Electron Laser Driven by Superconducting RF Accelerator 1094
 
  • P. Musumeci, P.E. Denham, A.C. Fisher, Y. Park
    UCLA, Los Angeles, California, USA
  • R.B. Agustsson, T.J. Hodgetts, A.Y. Murokh, M. Ruelas
    RadiaBeam, Santa Monica, California, USA
  • L. Amoudry
    Université Paris-Saclay, CNRS/IN2P3, IJCLab, Orsay, France
  • D.R. Broemmelsiek, S. Nagaitsev, J. Ruan, J.K. Santucci, G. Stancari, A. Valishev
    Fermilab, Batavia, Illinois, USA
  • D.L. Bruhwiler, J.P. Edelen, C.C. Hall
    RadiaSoft LLC, Boulder, Colorado, USA
  • A.H. Lumpkin, A. Zholents
    ANL, Lemont, Illinois, USA
  
  Funding: This work is supported by DOE grants DE-SC0017102, DE-SC0018559 and DE-SC0009914
In this paper we’ll describe the FAST-GREENS experimental program where a 4 m-long strongly tapered helical undulator with a seeded prebuncher is used in the high gain TESSA regime to convert a significant fraction (up to 10 %) of energy from the 240 MeV electron beam from the FAST linac to coherent 515 nm radiation. We’ll also discuss the longer term plans for the setup where by embedding the undulator in an optical cavity matched with the high repetition rate from the superconducting accelerator (3,9 MHz), a very high average power laser source can be obtained. Eventually, the laser pulses can be redirected onto the relativistic electrons to generate by inverse compton scattering a very high flux of circularly polarized gamma rays for polarized positron production. 		 
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2022-TUPOPT038  
About • Received ※ 09 June 2022 — Revised ※ 12 June 2022 — Accepted ※ 12 June 2022 — Issue date ※ 02 July 2022
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TUPOPT039 Characterization of Diamond with Buried Boron-Doped Layer Developed for Q-Switching an X-Ray Optical Cavity 1097
 
  • R.A. Margraf, A. Halavanau, Z. Huang, J. Krzywiński, J.P. MacArthur, G. Marcus, M.L. Ng, A.R. Robert, R. Robles, T. Sato, D. Zhu
    SLAC, Menlo Park, California, USA
  • Z. Huang, F. Ke, R. Robles, Y. Zhong
    Stanford University, Stanford, California, USA
  • S.-K. Mo, Y. Zhong
    LBNL, Berkeley, California, USA
  • P. Pradhan
    ANL, Lemont, Illinois, USA
  • A.R. Robert
    MAX IV Laboratory, Lund University, Lund, Sweden
  • M.D. Ynsa
    UAM, Madrid, Spain
  
  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.
X-ray Free-Electron Laser Oscillators (XFELOs) and X-ray Regenerative Amplifier FELs (XRAFELs) are currently in development to improve longitudinal coherence and spectral brightness of XFELs. These schemes lase an electron beam in an undulator within an optical cavity to produce X-rays. X-rays circulate in the cavity and interact with fresh electron bunches to seed the FEL process over multiple passes, producing progressively brighter and more spectrally pure X-rays. Typically, the optical cavities used are composed of Bragg-reflecting mirrors to provide high reflectivity and spectral filtering. This high reflectivity necessitates special techniques to out-couple X-rays from the cavity to deliver them to users. One method involves "Q-switching" the cavity by actively modifying the reflectivity of one Bragg-reflecting crystal. To control the crystal lattice constant and thus reflectivity, we use an infrared laser to heat a buried boron layer in a diamond crystal. Here, we build on earlier work in Krzywinski et al.* and present the current status of our Q-switching diamond, including implantation with 9 MeV boron ions, annealing, characterization and early tests.
*Krzywinski et al., "Q-switching of X-Ray Optical Cavities by using Boron Doped Buried Layer under a Surface of a Diamond Crystal," Proceedings of FEL2019, Hamburg, Germany, TUP033, 2019. 		 
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2022-TUPOPT039  
About • Received ※ 08 June 2022 — Revised ※ 15 June 2022 — Accepted ※ 15 June 2022 — Issue date ※ 08 July 2022
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TUPOPT044 High-Power Attosecond Pulses via Cascaded Amplification 1101
 
  • P.L. Franz, Z.H. Guo, S. Li, R. Robles
    Stanford University, Stanford, California, USA
  • D.K. Bohler, D.B. Cesar, X. Cheng, J.P. Cryan, T.D.C. Driver, J.P. Duris, A. Kamalov, S. Li, A. Marinelli, R. Obaid, R. Robles, N.S. Sudar, A.L. Wang, Z. Zhang
    SLAC, Menlo Park, California, USA
  
  Funding: This work was supported by US Department of Energy Contracts No. DE-AC02-76SF00.
The timescale for electron motion in molecular systems is on the order of hundreds of attoseconds, and thus the time-resolved study of electronic dynamics requires a source of sub-femtosecond x-ray pulses. Here we report the experimental generation of sub-femtosecond duration soft x-ray free electron laser (XFEL) pulses with hundreds of microjoules of energy using fresh-slice amplification in two cascaded stages at the Linac Coherent Light Source. In the first stage, an enhanced self-amplified spontaneous emission (ESASE) pulse is generated using laser-shaping of the electron beam at the photocathode*. The electron bunch is then delayed relative to the pulse by a magnetic chicane, allowing the radiation to slip onto a fresh slice of the bunch, which amplifies the ESASE pulse in the second cascade stage. Angular streaking** characterizes the experimental pulse durations as sub-femtosecond at ~465 eV in the experiment.
* Zhang, Z. et al. New J. Phys. 22 (2020)
** Li, S. et al. Optics Express 26.4 (2018): 4531-4547.
 		 
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2022-TUPOPT044  
About • Received ※ 08 June 2022 — Revised ※ 15 June 2022 — Accepted ※ 16 June 2022 — Issue date ※ 21 June 2022
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TUPOPT046 Electron Transport for the LCLS-II-HE Low Emittance Injector 1103
 
  • Y.M. Nosochkov, C. Adolphsen, R. Coy, C.E. Mayes, T.O. Raubenheimer, M.D. Woodley
    SLAC, Menlo Park, California, USA
  
  Funding: Work supported by the Department of Energy Contract DE-AC02-76SF00515.
The Low Emittance Injector (LEI) is a recent addition to the LCLS-II High Energy (LCLS-II-HE) Project under design at SLAC National Accelerator Laboratory. It will provide a second beam source capable of producing a low emittance electron beam that increases the XFEL photon energy reach to 20 keV. The LEI will include an SRF electron gun, a buncher system, a 1.3 GHz cryomodule, and a beam transport system with a connection to the LCLS-II beamline and a stand-alone diagnostic line. The LEI transport beamlines and diagnostic are discussed. 		 
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2022-TUPOPT046  
About • Received ※ 08 June 2022 — Accepted ※ 17 June 2022 — Issue date ※ 08 July 2022  
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TUPOPT047 Progress Report on Population Inversion X-Ray Laser Oscillator at LCLS 1107
 
  • A. Halavanau, R. Alonso-Mori, A. Aquila, U. Bergmann, F.-J. Decker, F. Fuller, M. Liang, A.A. Lutman, R.A. Margraf, R.H. Paul, C. Pellegrini
    SLAC, Menlo Park, California, USA
  • R. Ash, N.B. Welke
    UW-Madison/PD, Madison, Wisconsin, USA
  • A.I. Benediktovitch
    DESY, Hamburg, Germany
  • S.C. Krusic
    JSI, Ljubljana, Slovenia
  • N. Majernik, P. Manwani, J.B. Rosenzweig
    UCLA, Los Angeles, California, USA
  • R. Robles
    Stanford University, Stanford, California, USA
  • N. Rohringer
    Max Planck Institute for the Physics of Complex Systems, Dresden, Germany
  
  We report the progress in the design and construction of a population inversion x-ray laser oscillator (XLO) using LCLS as an x-ray laser pump, being developed by a SLAC, CFEL, University of Hamburg (Germany), University of Wisconsin, Josef Stefan Institute (Slovenia) and UCLA collaboration. In this proceeding, we will present the latest XLO design and numerical simulations substantiated by our first experimental results. In our next experimental step XLO will be tested on the Coherent X-ray Imaging (CXI) end-station at LCLS as a two pass Regenerative Amplifier operating at the Copper Kα1 photon energy of 8048 eV. When built, XLO will generate fully coherent transform limited pulses with about 50 meV FWHM bandwidth. We expect the XLO will pave the way for new user experiments, e.g. in inelastic x-ray scattering, parametric down conversion, quantum science, x-ray interferometry, and external hard x-ray XFEL seeding.  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2022-TUPOPT047  
About • Received ※ 12 June 2022 — Revised ※ 14 June 2022 — Accepted ※ 16 June 2022 — Issue date ※ 24 June 2022
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TUPOMS024 Sensitivity of EEHG Simulations to Dynamic Beam Parameters 1463
 
  • D. Samoilenko, W. Hillert, F. Pannek
    University of Hamburg, Institut für Experimentalphysik, Hamburg, Germany
  • S. Ackermann, E. Ferrari, N.S. Mirian, P. Niknejadi, G. Paraskaki, L. Schaper
    DESY, Hamburg, Germany
  • F. Curbis, M.A. Pop, S. Werin
    MAX IV Laboratory, Lund University, Lund, Sweden
  
  Currently, the Free electron laser user facility FLASH at DESY is undergoing a significant upgrade involving the complete transformation of one of its beamlines to allow external seeding. With the Echo-Enabled Harmonic Generation (EEHG) seeding method, we aim for the generation of fully coherent XUV and soft X-ray pulses at wavelengths down to 4 nm. The generated FEL radiation is sensitive to various electron beam properties, e.g., its energy profile imprinted either deliberately or by collective effects such as Coherent Synchrotron Radiation (CSR). In dedicated particle tracking simulations, one usually makes certain assumptions concerning the beam properties and the collective effects to simplify implementation and analysis. Here, we estimate the influence of some of the common assumptions made in EEHG simulations on the properties of the output FEL radiation, using the example of FLASH and its proposed seeding beamline. We conclude that the inherent properties of the FLASH1 beam, namely the negatively chirped energy profile, has dominant effect on the spectral intensity profile of the radiators output compare to that of the CSR induced chirp.  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2022-TUPOMS024  
About • Received ※ 20 May 2022 — Revised ※ 12 June 2022 — Accepted ※ 24 June 2022 — Issue date ※ 29 June 2022
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TUPOMS053 Start-to-End Simulations of the LCLS-II HE Free Electron Laser 1549
 
  • D.B. Cesar, G. Marcus, H.-D. Nuhn, T.O. Raubenheimer
    SLAC, Menlo Park, California, USA
  • J. Qiang
    LBNL, Berkeley, California, USA
  
  Funding: This work is supported in part by DOE Contract No. DE-AC02-76SF00515
In this proceeding we present start-to-end simulations of the LCLS-II-HE free electron laser. The HE project will extend the LCLS-II superconducting radio-frequency (SRF) linac from 4 GeV to 8 GeV in order to produce hard x-rays from the eponymous hard x-ray undulators (26 mm period). At the same time, soft x-ray performance is preserved (and extended into the tender regime) by using longer period undulators (56 mm period) than were originally built for LCLS-II (39 mm period). Here we use high-fidelity numerical particle simulations to study the performance of several SASE beamline configurations, and compare the resulting x-ray energy, power, duration, and transverse properties. Using the LCLS-II normal-conducting gun, we find that the x-ray pulse energy drops off rapidly above ~15 keV, while using the lower emittance beam from a proposed SRF gun, we improve the cutoff to ~20 keV. 		 
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2022-TUPOMS053  
About • Received ※ 08 June 2022 — Revised ※ 13 June 2022 — Accepted ※ 16 June 2022 — Issue date ※ 21 June 2022
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THOXSP3 Path to High Repetition Rate Seeding: Combining High Gain Harmonic Generation with an Optical Klystron 2411
 
  • G. Paraskaki, E. Ferrari, L. Schaper, E. Schneidmiller
    DESY, Hamburg, Germany
  • E. Allaria
    Elettra-Sincrotrone Trieste S.C.p.A., Basovizza, Italy
  • W. Hillert
    University of Hamburg, Institut für Experimentalphysik, Hamburg, Germany
  
  External seeding in combination with harmonic generation has become a hot topic in the field of high gain free-electron lasers (FELs) since it allows delivery of superior FEL radiation characterized by, for example, full coherence and unprecedented shot-to-shot stability. At low repetition rate machines operating at few 10 Hz, novel experiments have been realized already, however, at superconducting machines, current laser technology does not support exploiting the full repetition rate available. One way to overcome this problem is to reduce the requirements in seed laser power: here, an optical klystron based high gain harmonic generation (HGHG) setup is proposed to reduce the laser peak power requirements by orders of magnitude, enabling operation at drastically increased repetition rates. We report simulation results based on the seeded beamline concept of the FLASH2020+ project. Among other topics, the effect of a linear electron beam energy chirp on this setup will be discussed.  
slides icon Slides THOXSP3 [1.502 MB]  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2022-THOXSP3  
About • Received ※ 08 June 2022 — Revised ※ 14 June 2022 — Accepted ※ 16 June 2022 — Issue date ※ 27 June 2022
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