02 Photon Sources and Electron Accelerators
A06 Free Electron Lasers
Paper Title Page
MOYGB2 The LCLS-II: A High Power Upgrade to the LCLS 18
 
  • J.N. Galayda
    SLAC, Menlo Park, California, USA
  
  Funding: The work is supported by DOE under grant No. DE-AC02-76SF00515
The LCLS-II is an upgrade of the LCLS X-ray FEL based on a 4 GeV superconducting RF linac. The LCLS-II is designed to produce 100's of Watts of X-rays from 200 eV up to 5 keV. The linac uses 1.3 GHz 9-cell cavities processed using the N2-doping technique and will be the first large scale CW SCRF linac with a Q of roughly 3x1010 at a gradient of 16 MV/m. The injector which will be commissioned in spring 2018, is based on the normal conducting CW RF APEX gun developed at LBNL. The LCLS-II will have two undulators: the soft X-ray undulator is a 39 mm period hybrid PM with an adjustable vertical gap to cover the range from 200 eV to 1.5 keV and hard X-ray undulator is a novel adjustable horizontal gap hybrid PM undulator with 26 mm period to generate vertically polarized X-rays from 1 to 5 keV. The talk will review the performance goals as well as the hardware fabrication. 		 
slides icon Slides MOYGB2 [11.367 MB]  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2018-MOYGB2  
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MOZGBD1 Towards Full Performance Operation of SwissFEL 24
 
  • T. Schietinger
    PSI, Villigen PSI, Switzerland
  
  SwissFEL is the new X-ray free-electron laser facility at the Paul Scherrer Institute (PSI) in Switzerland. It was inaugurated in December 2016 and saw its first pilot experiments at the end of 2017. We describe the commissioning steps leading to the first phase of pilot experiments and outline the plans towards reaching nominal performance levels in 2018.  
slides icon Slides MOZGBD1 [11.391 MB]  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2018-MOZGBD1  
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MOZGBD2 FEL Performance Achieved at European XFEL 29
 
  • M. Scholz
    DESY, Hamburg, Germany
  
  The European XFEL has achieved first lasing by mid-2017 and first user experiments started by the end of that year. This invited talk describes the status of this facility, presenting highlights from the construction and commissioning, outlining experience from early operation, and discussing potential future developments.  
slides icon Slides MOZGBD2 [18.822 MB]  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2018-MOZGBD2  
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MOZGBD4
 Toward 10 fs Timing Stability of PAL-XFEL  
 
  • C.-K. Min, I. Eom, J. Hu, S.H. Jung, H.-S. Kang, S.H. Kim, H.-S. Lee, S.S. Park
    PAL, Pohang, Kyungbuk, Republic of Korea
  
  PAL-XFEL demonstrates 20 fs jitter in e-bunch arrival time at the end of undulators and its pump-probe system, which is extremely useful for maintaining high stability of machine and time-resolved experiments with high time resolution. Our low phase noise timing system and high stability high power RF system enable this low jitter. Our measurement shows 10 fs jitter of e-bunch arrival time at the injector and it increased ~20 fs due to e-bunch energy variation. The possibility of improving the final jitter is described based on the optimization of bunch compressors and longitudinal feedback.  
slides icon Slides MOZGBD4 [14.381 MB]  
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MOZGBD5 A Proposal for Coherent Hard X-Ray Generation Based on Two-Stage EEHG 38
 
  • Z.T. Zhao, J.H. Chen, C. Feng, Z. Wang, K.Q. Zhang
    SINAP, Shanghai, People's Republic of China
  
  A two stage echo-enabled harmonic generation (EEHG) scheme to produce coherent hard X-rays is presented. Electron bunchs of quite different lengths are separately used in each stage of EEHG and a monochromator is employed to purify the radiation from the first stage for seeding the second one. Theoretical analysis and 3D simulations show that the proposed scheme can generate fully coherent hard X-ray pulses directly from a conventional UV seed laser.  
slides icon Slides MOZGBD5 [7.330 MB]  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2018-MOZGBD5  
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TUPMF005 Simulation of Inverse Compton Scattering and Its Implications on the Scattered Linewidth 1254
SUSPF014   use link to see paper's listing under its alternate paper code  
 
  • N. Ranjan, B. Terzić
    ODU, Norfolk, Virginia, USA
  • I. Drebot, L. Serafini
    Istituto Nazionale di Fisica Nucleare, Milano, Italy
  • G.A. Krafft
    JLab, Newport News, Virginia, USA
  • V. Petrillo
    Universita' degli Studi di Milano & INFN, Milano, Italy
  
  Funding: This paper is authored by Jefferson Science Associates, LLC under U.S. DOE Contract No. DE-AC05-06OR23177.
Compton scattering, though first described some one hundred years ago, has recently experienced a surge of interest due to the search for energy sources that are capable of yielding low emission bandwidths. In particular, the desire for hard x-rays with energies greater than 10 keV has led to increased study of inverse Compton sources. The rise in interest concerning inverse Compton sources has increased the need for efficient models that properly quantify the behavior of scattered radiation given a set of interaction parameters. The current, state-of-the-art, simulations rely of Monte Carlo-based methods, which may fail to properly model collisions of bunches in low-probability regions of the spectrum. Furthermore, the random sampling of the simulations may lead to inordinately high runtimes. Our methods can properly model behaviors exhibited by the collisions by integrating over the emissions of the electrons in the bunch in a lessened amount of time. Analytical simulations of Gaussian laser beams closely verify the behavior predicted by an analytically derived scaling law describing bandwidth of scattered radiation.
Current affiliation of primary author (Nalin Ranjan) is Princess Anne High, Virginia Beach, VA 23452, USA. 		 
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2018-TUPMF005  
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TUPMF006 Pulsed Wire Measurements of a High Field Gradient Quadrupole Wiggler 1257
 
  • M. Kasa, A. Zholents
    ANL, Argonne, Illinois, USA
  
  Funding: Work supported by the U.S. Department of Energy, Office of Science, under Contract No. DE-AC02-06CH11357.
Alignment of the quadrupoles in a quadrupole wiggler to sub micrometer precision is required for the collinear wakefield accelerator that is under consideration at Argonne National Laboratory for a compact Free-Electron Laser [1]. The pulsed wire measurement method is the only technique that we are aware of that allows for sub micrometer precision and the ability to distinguish between the various quadrupoles within the wiggler. A one period prototype wiggler was manufactured and subsequently measured using the pulsed wire technique. The goal of the measurements was to verify that the magnetic centers of each quadrupole could be located and aligned to each other within the required precision. The method and results are described.
[1] A. Zholents, et al., "A preliminary design of the collinear dielectric wakefield accelerator", Nucl. Instrum. Meth. A829 (2016) 190-193. 		 
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2018-TUPMF006  
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TUPMF044 First Lasing of the CAEP THz FEL Facility Driven by a Superconducting Accelerator 1349
 
  • D. Wu, W. Bai, D.R. Deng, C.L. Lao, M. Li, S.F. Lin, X. Luo, L.J. Shan, X. Shen, H. Wang, J. Wang, Y. Xu, L.G. Yan, X. Yang, K. Zhou
    CAEP/IAE, Mianyang, Sichuan, People's Republic of China
  • Y.H. Dou, X.J. Shu
    Institute of Applied Physics and Computational Mathematics, People's Republic of China
  • W.-H. Huang
    TUB, Beijing, People's Republic of China
  • X.Y. Lu
    PKU, Beijing, People's Republic of China
  
  Funding: Work supported by China National Key Scientific Instrument and Equipment Development Project (2011YQ130018), National Natural Science Foundation of China (11475159, 11505173, 11575264 and 11605190)
The stimulated saturation of the terahertz free electron laser at China Academy of Engineering Physics was reached in August, 2017. This THz FEL facility consists of a GaAs photocathode high-voltage DC gun, a superconducting RF linac, a planar undulator and a quasi-concentric optical resonator. The terahertz wave frequency is continuous adjustable from 2 THz to 3 THz. The average power is more than 10 W and the micro-pulse power is more than 0.3 MW. 		 
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2018-TUPMF044  
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TUPMF051 Generating Ultrashort X-Ray Pulse in a Diffraction-Limed Storage Ring by Phase-Merging Enhanced Harmonic Generation with Normal Modulator 1371
 
  • W. Liu, Y. Jiao
    IHEP, Beijing, People's Republic of China
  
  In recent years, the study of ultrafast processes has increased the demand for ultrashort pulses. The duration of the synchrotron radiation pulse is generally in the range of 10-100 ps, which cannot be used in the experiments of studying the ultrafast process. Thus it is interesting to explore a way of obtaining sub-picosecond radiation pulses in storage ring light sources. The phase-merging enhanced harmonic generation (PEHG) scheme using a transverse gradient undulator as the modulator can be used to generate coherent radiation at high harmonic, which is very suitable for the generating ultrashort pulses in a diffraction-limed storage ring (DLSR). This paper presents a new PEHG modulation scheme, using a normal undulator as the modulator. This scheme is technically easier to be realized in a DLSR. Simulation is performed to demonstrate the effectiveness of this method.  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2018-TUPMF051  
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TUPMF069 Low Gain FEL Oscillator Option for PETRA IV 1420
 
  • I.V. Agapov
    DESY, Hamburg, Germany
  • Y.-C. Chae
    ANL, Argonne, Illinois, USA
  • W. Hillert
    University of Hamburg, Institut für Experimentalphysik, Hamburg, Germany
  
  Next generation synchrotron storage rings will have electron beam density approaching that necessary for driving an XFEL. It falls short of the quality required for the high-gain x-ray regime above 1 keV, mainly due to the large energy spread and small peak current, bit is sufficient to reach low-gain regime. Here we explore the parameter space of a low gain XFEL oscillator, to establish the feasibility range of such a device for the Petra upgrade project.  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2018-TUPMF069  
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TUPMF076 Temporal X-ray Reconstruction Using Temporal and Spectral Measurements 1440
SUSPF010   use link to see paper's listing under its alternate paper code  
 
  • F. Christie, J. Rönsch-Schulenburg, M. Vogt
    DESY, Hamburg, Germany
  • Y. Ding, Z. Huang, J. Krzywinski, A.A. Lutman, T.J. Maxwell, D.F. Ratner
    SLAC, Menlo Park, California, USA
  • V. A. Jhalani
    CALTECH, Pasadena, California, USA
  
  Transverse deflecting structures (TDS) are widely used in accelerator physics to measure the longitudinal density of particle bunches. When used in combination with a dispersive section, the whole longitudinal phase space density can be imaged. At the Linac Coherent Light Source (LCLS), the installation of such a device downstream of the undulators enables the reconstruction of the X-ray temporal intensity profile by comparing longitudinal phase space distributions with lasing on and lasing off*. However, the resolution of this TDS is limited to around 1 fs rms (root mean square), and therefore, in most cases, it is not possible to resolve single self-amplified spontaneous emission (SASE) spikes within one photon pulse. By combining the intensity spectrum from a high resolution photon spectrometer** and the temporal structure from the TDS, the overall resolution is enhanced, thus allowing the observation of temporal, single SASE spikes. The combined data from the spectrometer and the TDS is analyzed using an iterative algorithm to obtain the actual intensity profile. In this paper, we present the reconstruction algorithm as well as analyzed data obtained from simulations which shows the reliability of this method. Real data will be published at a later stage.
*Y. Ding et al., Phys. Rev. ST AB, 14, 120701, 2011.
**D. Zhu et al., Appl. Phys. Lett., 101, 034103, 2012. 		 
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2018-TUPMF076  
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TUPMF078 Control of FEL Radiation Properties by Tailoring the Seed Pulses 1444
 
  • V. Grattoni, R.W. Aßmann, J. Bödewadt, I. Hartl, C. Lechner, B. Manschwetus, M.M. Mohammad Kazemi
    DESY, Hamburg, Germany
  • A. Azima, W. Hillert, V. Miltchev, J. Roßbach
    University of Hamburg, Institut für Experimentalphysik, Hamburg, Germany
  • S. Khan, T. Plath
    DELTA, Dortmund, Germany
  
  Seeded free-electron lasers (FELs) produce intense, ultrashort and fully coherent X-ray pulses. These seeded FEL pulses depend on the initial seed properties. Therefore, controlling the seed laser allows tailoring the FEL radiation for phase-sensitive experiments. In this contribution, we present detailed simulation studies to characterize the FEL process and to predict the operation performance of seeded pulses. In addition, we show experimental data on the temporal characterization of the seeded FEL pulses performed at the sFLASH experiment in Hamburg.  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2018-TUPMF078  
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TUPMF079 An Option to Generate Seeded FEL Radiation for FLASH1 1448
 
  • V. Grattoni, R.W. Aßmann, J. Bödewadt, I. Hartl, C. Lechner, B. Manschwetus, M.M. Mohammad Kazemi
    DESY, Hamburg, Germany
  • W. Hillert, V. Miltchev, J. Roßbach
    University of Hamburg, Institut für Experimentalphysik, Hamburg, Germany
  • S. Khan, T. Plath
    DELTA, Dortmund, Germany
  
  The FLASH free-electron laser (FEL) at DESY is currently operated in self-amplified spontaneous emission (SASE) mode in both beamlines FLASH1 and FLASH2. Seeding offers unique properties for the FEL pulse, such as full coherence, spectral and temporal stability. In this contribution, possible ways to carry the seeded FEL radiation to the user hall are presented with analytical considerations and simulations. For this, components of the sFLASH seeding experiment are used.  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2018-TUPMF079  
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TUPMF080 Progress on Multibunch FEL Performance at FLASH 1452
 
  • T. Hellert, Ch. Schmidt
    DESY, Hamburg, Germany
  
  At the SASE-FEL user facility FLASH, superconducting TESLA-type cavities are used for acceleration. The high achievable duty cycle allows for operating with long bunch-trains, hence considerably increasing the efficiency of the machine. However, RF induced intra-bunch-train trajectory variations were found to be responsible for significant variations of the SASE intensity within one bunch train. This work presents the latest achievements in improving the multi-bunch FEL performance by reducing the intra-bunch-train variation of RF parameters. Particular attention is given to the static and dynamic detuning of the cavities. It will be shown that the current level of LLRF control is suitable to limit the variation of RF parameters considerably.  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2018-TUPMF080  
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TUPMF081 Microphonic Detuning Induced Coupler Kick Variation at LCLS-II 1456
 
  • T. Hellert
    DESY, Hamburg, Germany
  • W. Ackermann, H. De Gersem
    TEMF, TU Darmstadt, Darmstadt, Germany
  • C. Adolphsen, Z. Li, C.E. Mayes
    SLAC, Menlo Park, California, USA
  
  The LCLS-II free-electron laser will be an upgrade of the existing Linac Coherent Light Source (LCLS), including a 4 GeV CW superconducting linac based on the TESLA technology. The high quality factor of the cavity makes it very sensitive to vibrations. The shift of its eigenfrequency (i.e., detuning) will be compensated by the power source in order to assure a constant accelerating voltage. Significant variations of the forward power are expected which result in coupler kick variations induced by the fundamental power coupler. In this work we estimate the magnitude of trajectory jitter caused by these variations. High precision 3D field maps including standing and traveling-wave components for a cavity with the LCLS-II coupler design are presented.  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2018-TUPMF081  
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TUPMF082 FLASHForward: DOOCS Control System for a Beam-Driven Plasma-Wakefield Acceleration Experiment 1460
 
  • S. Karstensen, S. Bohlen, J. Dale, M. Dinter, J.M. Müller, P. Niknejadi, J. Osterhoff, K. Poder, P. Pourmoussavi, V. Rybnikov, L. Schaper, B. Schmidt, J.-P. Schwinkendorf, B. Sheeran, G.E. Tauscher, S. Thiele, S. Wesch, P. Winkler
    DESY, Hamburg, Germany
  
  The FLASHForward project at DESY is an innovative beam-driven plasma-wakefield acceleration experiment integrated in the FLASH facility, aiming to accelerate electron beams to GeV energies over a few centimetres of ionised gas. These accelerated beams are tested for their capability to demonstrate exponential free-electron laser gain; achievable only through rigorous analysis of both the driver and witness beam's phase space. The thematic priority covered in here the control system part of FLASHForward. To be able to control, read out and save data from the diagnostics into DAQ, the DOOCS control system has been integrated into FLASH Forward. Laser beam control, over 70 cameras, ADCs, timing system and motorised stages are combined into the one DOOCS control system as well as vacuum and magnet controls. Micro TCA for Physics (MTCA.4) is the solid basic computing system, supported from high power workstations for camera read-out and normal Linux computers.  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2018-TUPMF082  
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TUPMF085 Status of the sFLASH Experiment 1471
 
  • C. Lechner, R.W. Aßmann, J. Bödewadt, V. Grattoni, I. Hartl, T. Laarmann, M.M. Mohammad Kazemi, A. Przystawik
    DESY, Hamburg, Germany
  • A. Azima, H.B. Biss, M. Drescher, W. Hillert, L.L. Lazzarino, V. Miltchev, J. Roßbach
    University of Hamburg, Institut für Experimentalphysik, Hamburg, Germany
  • S. Khan, T. Plath
    DELTA, Dortmund, Germany
  
  Funding: This work is supported by the Federal Ministry of Education and Research of Germany within FSP-302 under FKZ 05K13GU4, 05K13PE3, and 05K16PEA.
The sFLASH experiment at the free-electron laser (FEL) FLASH1 is a setup for the investigation of external FEL seeding. Since 2015, the seeding scheme high-gain harmonic generation (HGHG) is being studied. At the end of the seeded FEL, an RF deflector enables time-resolved analysis of the seeded electron bunches while the photon pulses can be characterized using the technique of THz streaking. In this contribution, we present the current configuration of the experiment and give an overview of recent experimental results. 		 
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2018-TUPMF085  
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TUPMF089 Possible Upgrades of FLASH –- A View from the Accelerator-Perspective 1477
 
  • M. Vogt, B. Faatz, K. Honkavaara, J. Rönsch-Schulenburg, S. Schreiber, J. Zemella
    DESY, Hamburg, Germany
  
  Recently FLASH (Free electron LASer in Hamburg) at DESY has been granted funding for a refurbishment project covering among others the replacement of two old SRF modules, an upgrade of the injector lasers and an upgrade of parts of the electron beam diagnostics. In addition we are proposing several possible upgrades and new features for the injector and the drive linac as well as in the undulator beamlines. Here we present options which are in our opinion technically feasible and at the same time operationally manageable.  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2018-TUPMF089  
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TUPMF090 Status of the Superconducting Soft X-Ray Free-Electron Laser FLASH at DESY 1481
 
  • M. Vogt, K. Honkavaara, M. Kuhlmann, J. Rönsch-Schulenburg, S. Schreiber, R. Treusch
    DESY, Hamburg, Germany
  
  FLASH, the free-electron laser (FEL) user facility at DESY, has delivered high brilliance VUV and soft x-ray FEL radiation for photon experiments since summer 2005. In 2014 and 2015 a second beamline, FLASH2, has been commissioned in parallel to user operation at FLASH1. FLASH's superconducting linac can produce bunch trains of up to 800 bunches within a 0.8 ms RF flat top at a repetition rate of 10 Hz. In standard operation during 2017 FLASH supplied up to 500 bunches in two bunch trains with independent fill patterns and compression schemes. Since mid 2017 initial commissioning of a third experimental beamline, accommodating the FLASHForward plasma wakefield acceleration experiment, has started. We report on the highlights of the FLASH operation in 2017/2018.  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2018-TUPMF090  
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TUPML035 FELs Driven by Laser Plasma Accelerators Operated with Transverse Gradient Undulators 1615
 
  • F. Jafarinia, R.W. Aßmann, F. Burkart, U. Dorda, C. Lechner, B. Marchetti, R. Rossmanith, P.A. Walker
    DESY, Hamburg, Germany
  • A. Bernhard, R. Rossmanith
    KIT, Karlsruhe, Germany
  
  Laser Plasma Accelerators produce beams with a significantly higher energy spread (up to a few percent) compared to conventional electron sources. The high energy spread increases significantly the gain length when used for an FEL. In order to reduce the gain length of the FEL the Transverse Gradient Undulators (TGUs) instead of conventional undulators were proposed. In this paper the limits of this concept are discussed using a modified Version of the GENESIS program*.
*Zhirong Huang et al., Phys. Rev. Lett., 109, 204801 		 
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2018-TUPML035  
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WEXGBD2 Pulse-by-Pulse Multi-XFEL Beamline Operation with Ultra-Short Laser Pulses 1740
 
  • T. Hara, T. Inagaki, H. Maesaka, Y. Otake, H. Tanaka, K. Togawa
    RIKEN SPring-8 Center, Sayo-cho, Sayo-gun, Hyogo, Japan
  • K. Fukami
    JASRI/SPring-8, Hyogo-ken, Japan
  • T. Hasegawa, O. Morimoto, S. Nakazawa, M. Yoshioka
    SES, Hyogo-pref., Japan
  • H. Kawaguchi, Y. Kawaguchi
    Nichicon (Kusatsu) Corporation, Shiga, Japan
  • C. Kondo
    JASRI, Hyogo, Japan
  
  The parallel operation of multiple beamlines is an important issue to expand the opportunity of user experiments for linac based FELs. At SACLA, the parallel operation of three beamlines, BL1~3, has been open to user experiments since September 2017. BL1 is a soft x-ray beamline driven by a dedicated accelerator, which is a former SCSS linac, and BL2 and 3 are XFEL beamlines, which share the electron beam from the SACLA main linac. In the parallel operation, a kicker magnet with 10 ppm stability (peak-to-peak) switches the two XFEL beamlines at 60 Hz from pulse to pulse. To ensure wide spectral tunability and optimize the laser performance, the energies and lengths of the electron bunches are independently adjusted for the two beamlines according to user experiments. Since the electron bunch of SACLA has typically 10~15 fs (FWHM) in length and its peak current exceeds 10 kA, the CSR effect at a dogleg beam transport to BL2 is quite significant. In order to suppress the CSR effects, an isochronous and achromatic lattice based on two DBA structures was introduced. In this talk, the multiple XFEL beamline operation and achieved laser performance are presented.  
slides icon Slides WEXGBD2 [9.708 MB]  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2018-WEXGBD2  
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WEXGBD3
 Towards Attosecond Science at LCLS and LCLS-II  
 
  • A. Marinelli
    SLAC, Menlo Park, California, USA
  
  Time-resolved experiments at the attosecond scale hold great promise for understanding ultrafast electron dynamics in molecules, as well as the role of electron coherence in chemistry. In the recent past, much progress has been made in using X-ray free-electron lasers (X-FELs) to visualize atomic motion at the tens of femtosecond scale. At the same time, table-top lasers have been operated at the attosecond scale and successfully employed in scientific experiments. However, the femtosecond barrier has not yet been broken at X-ray free-electron lasers, hindering our ability to understand the fundamental motion of electrons. This invited talk describes the XLEAP project, aimed at generating attosecond pulses in the soft-X-ray region at LCLS, including the physics of laser-enhanced FELs and the effect of bandwidth broadening in this FEL mode. This talk will also present early XLEAP commissioning results and the immediate experimental plans, and describe plans for the transition from FEL R&D to science and discuss the roadmap to attosecond science with LCLS-II.  
slides icon Slides WEXGBD3 [15.820 MB]  
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THXGBD2 Overview of Undulator Concepts for Attosecond Single-Cycle Light 2878
THPMK142   use link to see paper's listing under its alternate paper code  
 
  • A. Mak, V.A. Goryashko, P.M. Salen, G. K. Shamuilov
    Uppsala University, Uppsala, Sweden
  • D.J. Dunning, N. Thompson
    STFC/DL/ASTeC, Daresbury, Warrington, Cheshire, United Kingdom
  • D.J. Dunning, B.W.J. MᶜNeil, N. Thompson
    Cockcroft Institute, Warrington, Cheshire, United Kingdom
  • J. Hebling, Z. Tibai, Gy. Tóth
    University of Pecs, Pécs, Hungary
  • Y. Kida, T. Tanaka
    RIKEN SPring-8 Center, Hyogo, Japan
  • B.W.J. MᶜNeil
    USTRAT/SUPA, Glasgow, United Kingdom
  
  Funding: Swedish Research Council (VR, 2016-04593); Stockholm-Uppsala Centre for Free-Electron Laser Research; C. F. Liljewalchs stipendiestiftelse.
The production of intense attosecond light pulses is an active area in accelerator research, motivated by the stringent demands of attosecond science: (i) short pulse duration for resolving the fast dynamics of electrons in atoms and molecules; (ii) high photon flux for probing and controlling such dynamics with high precision. While the free-electron laser (FEL) can deliver the highest brilliance amongst laboratory x-ray sources today, the pulse duration is typically 10-100 femtoseconds. A major obstacle to attaining attosecond duration is that the number of optical cycles increases with every undulator period. Hence, an FEL pulse typically contains tens or hundreds of cycles. In recent years, several novel concepts have been proposed to shift this paradigm, providing the basis for single-cycle pulses and paving the way towards high-brilliance attosecond light sources. This article gives an overview of these concepts. 		 
slides icon Slides THXGBD2 [1.758 MB]  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2018-THXGBD2  
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THPMF012 Tapered Flying Radiofrequency Undulator 4059
 
  • S.P. Antipov, S.V. Kuzikov, A. Liu
    Euclid TechLabs, LLC, Solon, Ohio, USA
  • S.V. Kuzikov, A.V. Savilov, A.A. Vikharev
    IAP/RAS, Nizhny Novgorod, Russia
  
  Funding: DOE SBIR DE-SC0017145
The x-ray free electron laser (x-FEL) efficiency, measured as a fraction of the electron beam power converted into light, is typically below 0.1% for most of the x-FEL facilities presently in operation. Undulator tapering techniques can be used to improve the conversion efficiency by 1-2 orders of magnitude. However at present there are no robust tapered undulator x-FEL schemes operating at 10% efficiency. In this paper we report on the development of tapered radiofrequency (RF) undulator. An RF undulator is a microwave waveguide in which strong RF field is excited that interacts with a charged particle beam forcing it to radiate coherent x-rays while undergoing a wiggling motion. RF undulators are attractive for use in x-FELs due to their large beam aperture and a short undulator period. Strongly tapered RF undulators (with tapering of a wavelength) due to non-resonant trapping regime allow keeping high overall XFEL efficiency being driven by laser plasma accelerated beams usually having high enough current but large energy spread (1-10%). 		 
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2018-THPMF012  
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THPMF016 Design of a Terahertz Radiation Source for Pump-Probe Experiments 4073
 
  • J. Pfingstner, E. Adli
    University of Oslo, Oslo, Norway
  • E. Marín
    CERN, Geneva, Switzerland
  • S. Reiche
    PSI, Villigen PSI, Switzerland
  
  Narrow-band, tuneable, high-power terahertz radiation is highly demanded for pump-probe experiments at light source facilities. Since the requested radiation properties are not well covered by current terahertz radiation sources, an accelerator-based terahertz source employing the slotted-foil technique in combination with transverse deflecting cavities is proposed in this work. A detailed design has been worked out, and the behaviour of the electron beam and the created terahertz radiation is studied via numerical simulations. The results show that the proposed source produces tuneable terahertz radiation that can meet most of the demanded specifications.  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2018-THPMF016  
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THPMF050 High-Efficient XFELO Based on Optical Resonator with Self-Modulated Q-Factor 4172
 
  • S.V. Kuzikov, A.V. Savilov, A.A. Vikharev
    IAP/RAS, Nizhny Novgorod, Russia
  • S.P. Antipov, S.V. Kuzikov
    Euclid TechLabs, LLC, Solon, Ohio, USA
  
  In this paper we describe an efficient XFELO having a new non-stationary out-coupling scheme. It consists of two undulator sections placed inside optical cavity. The first section is a conventional uniform undulator and the second one is a tapered undulator. At start time point X-ray radiation is mostly produced by the uniform section. Mirrors of XFELO's optical resonator are designed so that diffraction Q-factor reaches the highest value, i.e losses are near zero. As X-ray power increases the tapered undulator begins to contribute more to radiation power. However a portion of that power misses mirrors of the optical cavity, because those are tuned to confine radiation produced by the first undulator. This process establishes a steady state operation of the XFELO.  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2018-THPMF050  
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THPMF082 Suppression of Microbunching Instability Using a Quadrupole Inserted Chicane in Free-Electron-Laser Linacs 4267
SUSPF011   use link to see paper's listing under its alternate paper code  
 
  • B. Li, J. Qiang
    LBNL, Berkeley, California, USA
  
  The microbunching instability (MBI) driven by beam collective effects in a linear accelerator of a free-electron laser (FEL) facility can significantly degrade the electron beam quality and FEL performance. A method exploited longitudinal mixing derived from the natural transverse spread of the beam was proposed several years ago using two dipoles to suppress the instability. In this paper, instead of using bending magnets to introduce the transverse-to-longitudinal coupling, which will lead to an inconvenient deflection of the downstream beam line, we propose a scheme using a quadrupole inserted chicane to introduce the longitudinal mixing inside the accelerator transport system to suppress this instability. And we finally eliminate the transverse-to-longitudinal coupling after the dogleg section.  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2018-THPMF082  
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THPMF084 Numerical Shot Noise Modeling and Particle Migration Scheme 4274
 
  • K. Hwang, J. Qiang
    LBNL, Berkeley, California, USA
  
  Funding: US Department of Energy under Contract no. DEAC02-05CH11231
In order to model correct statistical properties of shot noise, special particle loading algorithms were developed and used in FEL community. However, the compatibility of such loading algorithms with particle migration scheme across numerical mesh is not well studied. Here, we address the necessity of special particle migration scheme for different loading algorithms and present a possible solution pair. 		 
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2018-THPMF084  
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THPMF086 Reliability Improvement on Wiggler Period Averaging Approximation 4281
 
  • K. Hwang, J. Qiang
    LBNL, Berkeley, California, USA
  
  Funding: US Department of Energy under Contract no. DEAC02-05CH11231
As the wiggler period averaging is subject to reliability issue, many efforts on FEL codes without such approximations are made at the cost of heavier computation loads. However, efforts toward increasing the reliability of such approximation are few. In this report, we present a new capability of IMPACT code suite based on such approximation with the addition of perturbative corrections to wiggler period averaging error. 		 
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2018-THPMF086  
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THPMK016 Simulation Study of the NSRRC High Brightness Linac System and Free Electron Laser 4329
 
  • W.K. Lau, C.H. Chen, H.P. Hsueh, N.Y. Huang
    NSRRC, Hsinchu, Taiwan
  • J. Wu
    SLAC, Menlo Park, California, USA
  
  A 263 MeV linac system has been designed to provide a high brightness electron beam for the NSRRC VUV FEL test facility. This system is equipped with a dogleg with linearization optics to compensate the effects of nonlinear energy chirps introduced into the system by the chirper linac voltage during bunch compression. In this study, we performed start-to-end simulation to illustrate the capability of this linac system to generate a beam that can be used to drive a SASE FEL to saturation within reasonable undulator length. It has been demonstrated that, for a 200 pC beam, such FEL has a saturated output power of ~200 MW at 6-m undulator length. Further optimization of bunch current profile and momentum spectrum is required.  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2018-THPMK016  
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THPMK022 Simulation for THz Coherent Undulator Radiation from Combination of Velocity Bunchings 4345
 
  • Y. Sumitomo, K. Hayakawa, Y. Hayakawa, K. Nogami, T. Sakai, Y. Takahashi, T. Tanaka
    LEBRA, Funabashi, Japan
  
  We study the effect of a combination of velocity bunchings and its application to THz coherent undulator radiation at LEBRA, Nihon U. by simulations. The velocity bunching is a technique that is commonly used to make the bunch length shorter at lower energies. However, since one velocity bunching has a correlation between bunch energy and length, we may not have so much room to change energies to obtain different coherent radiation wavelengths. Hence we propose a combination of velocity bunchings, that relaxes the restrictive correlation. We have three 4m traveling-wave accelerator tubes at LEBRA, Nihon U. The undulator is installed after the acceleration tubes and 2 x 45 degree bending magnets. Since the design of current undulator requires less than 25 MeV beam energy to obtain the radiation at THz region, the velocity bunching is reasonable for coherent radiation. We show the simulation results of a combination of velocity bunchings of the three tubes and the magnetic bunching at bending magnets, suitable for the coherent undulator radiation.  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2018-THPMK022  
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THPMK023 Coherent Transition Radiation Generated from Transverse Electron Density Modulation 4348
 
  • A. Halavanau, P. Piot
    Northern Illinois University, DeKalb, Illinois, USA
  • A.I. Benediktovitch
    BSU, Minsk, Belarus, Belarus
  • S.N. Galyamin, A.V. Tyukhtin
    Saint Petersburg State University, Saint Petersburg, Russia
  • P. Piot
    Fermilab, Batavia, Illinois, USA
  
  Coherent Transition radiation (CTR) of a given frequency is commonly generated with longitudinal electron bunch trains. In this paper we present a study of CTR production from electron transverse density modulation. We demonstrate via numerical simulations a simple technique to generate THz-scale frequencies from mm-scale transversely separated electron beamlets. The results and a potential experimental setup are discussed.  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2018-THPMK023  
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THPMK034 Study on Effect of Phase Shifter on FEL Intensity at PAL-XFEL 4372
 
  • C.H. Shim
    POSTECH, Pohang, Kyungbuk, Republic of Korea
  • J.H. Hong, H. Yang
    PAL, Pohang, Kyungbuk, Republic of Korea
  
  In the PAL-XFEL, the phase shifters are installed be-tween the undulator modules to match the phase of the electron beam and the FEL radiation field at the entrance of next undulator. By varying the phase shifter gap, the FEL intensity measured at the QBPM oscillates and sine curve fitting can be applied to it for optimizing the FEL intensity. However, the optimal gap determined from fitting result is slightly different from the gap at which the maximum intensity is measured because distorted shapes are appeared from some phase shifters. In this presentation, we report and discuss the experimental results of phase shifter gap scanning with simulation results.  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2018-THPMK034  
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THPMK035 Generation of Isolated Zeptosecond Pulse in Gamma-Ray Free Electron Laser 4375
 
  • C.H. Shim, D.E. Kim
    POSTECH, Pohang, Kyungbuk, Republic of Korea
  • Y.W. Parc
    PAL, Pohang, Kyungbuk, Republic of Korea
  
  An X-ray pulse with zeptosecond pulse duration is an essential tool to resolve the nuclear dynamics. To make such a short pulse duration, we need to make a very wide frequency range radiation which is known from the uncertainty principle. The spectral range of an isolated zeptosecond pulse has to be of order of few keV which is called as a gamma ray. In this presentation, the generation of an isolated zeptosecond pulses in the gamma-ray free electron laser is studied by the simulation.  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2018-THPMK035  
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THPMK042 Two and Multiple Bunches at LCLS 4378
 
  • F.-J. Decker, K.L.F. Bane, R.N. Coffee, W.S. Colocho, S. Gilevich, S.H. Glenzer, A.A. Lutman, A. Miahnahri, D.F. Ratner, J.C. Sheppard, S. Vetter
    SLAC, Menlo Park, California, USA
  
  The LCLS X-Ray FEL at SLAC typically delivers one bunch at the time. Different schemes of two pulses have been developed: Two bucket, Twin bunch, split undulator, and fresh slice. Here we discuss a four bunch or even eight bunch setup, where the separation between the individual bunches is two RF buckets: 0.7 ns.  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2018-THPMK042  
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THPMK043 Timing Stability at LCLS 4381
 
  • F.-J. Decker, R.N. Coffee, W.S. Colocho, J.M. Glownia, K. Gumerlock, B.L. Hill, T.J. Maxwell, J. May
    SLAC, Menlo Park, California, USA
  
  The beam stability of the LCLS (Linac Coherent Light Source) has increased substantially over the years. Transversely it is a fraction of the beam size. The energy jitter was reduced from five times the energy spread to a fraction of it. Only the timing jitter is left. It got improved during the energy jitter reduction, but typically left alone. So we have five dimensions of the six-dimensional phase space covered with feedbacks and special 60-Hz jitter setups which eliminate the difference between every other pulse, but not for the general timing setup. We describe a scheme with the RF of the XTCAV, which could be used for other setups like lasers.  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2018-THPMK043  
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THPMK045 Generation of High Power, High Intensity, Ultra Short X-Ray FEL Pulses 4384
 
  • M.W. Guetg, Y. Ding, Z. Huang, A.A. Lutman
    SLAC, Menlo Park, California, USA
  
  X-ray Free Electron Lasers combine high pulse power, short pulse length, narrow bandwidth and a high degree of transverse coherence. Any increase in the photon pulse power, while shortening the pulse length, will further push the frontier on several key XFEL applications including single molecule imaging and novel nonlinear X-ray methods. We will present experimental results at the Linac Coherent Light Source raising its maximum power to more than 300% of the current limit, while reducing the photon pulse length to 10 fs. This was achieved by minimizing residual transverse-longitudinal centroid beam offsets and beam yaw, and by correcting the dispersion when operating over 6 kA peak current with a longitudinally shaped beam.  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2018-THPMK045  
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THPMK046 Advanced Fresh-Slice Beam Manipulations for FEL X-Ray Applications 4387
 
  • A.A. Lutman, Y. Ding, M.W. Guetg, Z. Huang, J. Krzywinski, J.P. MacArthur, A. Marinelli, T.J. Maxwell
    SLAC, Menlo Park, California, USA
  • C. Emma
    UCLA, Los Angeles, USA
  
  The recent development of the Fresh-slice technique granted control on which temporal slice lases in each undulator section in an X-ray Free-electron laser. Fresh-slice has been used for several experiments at the Linac Coherent Light Source for the generation of customizable high power two-color beams, and increased the performance of self-seeding schemes. As a novel development of the technique we present the demonstration of multistage self-amplified spontaneous-emission amplification schemes for the production of high-power ultra short pulses and improved control of the temporal duration of each pulse in multi-pulse schemes.  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2018-THPMK046  
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THPMK051 Theoretical Formulation of Improved SASE FEL Based on Slippage Enhancement Scheme 4398
 
  • C.-Y. Tsai, J. Wu, C. Yang, G. Zhou
    SLAC, Menlo Park, California, USA
  • M. Yoon
    POSTECH, Pohang, Kyungbuk, Republic of Korea
  • G. Zhou
    IHEP, Beijing, People's Republic of China
  
  Funding: The work was supported by the US Department of Energy (DOE) under contract DE- AC02-76SF00515 and the US DOE Office of Science Early Career Research Program grant FWP-2013-SLAC-100164.
A method to improve the spectral brightness of self-amplified spontaneous emission (SASE) based on slippage enhancement has been proposed*, **. The implementation is to insert a series of magnetic chicanes to introduce a path-length delay of the electron beam to the radiation beam. By correlating the electron slices of neighboring cooperation distances this can lengthen the collective interaction and thus enhance the spectral brightness. In the existing literature most studies rely on numerical simulations and there is limited work on analytical analysis. In this paper we formulate the problem of slippage enhanced SASE (SeSASE) high-gain FEL with inclusion of by-pass magnetic chicanes. The analysis takes the finite energy spread of the electron beam and the nonzero momentum compaction of the chicane into consideration. The evolution of spectral bandwidth of SeSASE is compared with that of usual SASE in theory and numerical simulations. The effects of finite beam energy spread and non-isochronisity are also quantified.
*J. Wu et al., FEL2012
**B. W. J. McNeil et al., PRL 110, 134802 (2013) 		 
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2018-THPMK051  
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THPMK052 Numerical Simulation of Phase-Shift Method for Fel Power Enhancement in PAL-XFEL 4402
 
  • C.-Y. Tsai, J. Wu, C. Yang, G. Zhou
    SLAC, Menlo Park, California, USA
  • H.-S. Kang
    PAL, Pohang, Kyungbuk, Republic of Korea
  • M. Yoon
    POSTECH, Pohang, Kyungbuk, Republic of Korea
  • G. Zhou
    IHEP, Beijing, People's Republic of China
  
  Funding: The work was supported by the US Department of Energy (DOE) under contract DE- AC02-76SF00515 and the US DOE Office of Science Early Career Research Program grant FWP-2013-SLAC-100164.
Recently the phase jump method for efficiency enhancement in free-electron laser (FEL) was proposed*. One of the unique features of PAL-XFEL with phase shifters may be taken for the experimental demonstration of this phase jump scheme. In this paper we numerically investigate the scheme using the three-dimensional numerical simulation code GENESIS**. The physical parameters are based on hard x-ray line of PAL-XFEL***. The preliminary simulation results indicate that this potential phase jump scheme can enhance at least one order of magnitude of FEL power performance. Combination of this scheme with undulator tapering is also discussed in this paper.
*A. Mak, F. Curbis, and S. Werin, PRAB 20, 060703 (2017)
**S. Rieche, NIMA 429(1):243-248 (1999)
***I. S. Ko et al., Appl. Sci. 2017, 7, 479 (2017) 		 
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2018-THPMK052  
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THPMK053 Simulation for LCLS-II Hard X-ray Self Seeding Scheme 4406
 
  • C. Yang, Y. Feng, J. Krzywinski, T.O. Raubenheimer, C.-Y. Tsai, J. Wu, M. Yoon, G. Zhou
    SLAC, Menlo Park, California, USA
  • H.X. Deng
    SINAP, Shanghai, People's Republic of China
  • D.H. He
    USTC/NSRL, Hefei, Anhui, People's Republic of China
  • Y. Hong, B. Yang
    University of Texas at Arlington, Arlington, USA
  • X.F. Wang
    CIAE, Beijing, People's Republic of China
  • M. Yoon
    POSTECH, Pohang, Kyungbuk, Republic of Korea
  • G. Zhou
    IHEP, Beijing, People's Republic of China
  
  Funding: The work was supported by the US Department of Energy (DOE) under contract DE-AC02-76SF00515 and the US DOE Office of Science Early Career Research Program grant FWP-2013-SLAC-100164.
Typical SASE FELs have poor temporal coherence because of starting from shot noise. Self-seeding scheme is an approach to improve the longitudinal coherence. The single crystal monochromator self-seeding has been in successful operation in LCLS. For the high repetition rate LCLS-II machine, for damage consideration, it was initially proposed to have a two-stage self-seeding scheme, yet we have found the two-stage self-seeding scheme has no advantage over one-stage self-seeding scheme. In this paper, we investigate the optimal self-seeding configuration of LCLS-II for different photon energies, and present a comparison between one-stage and two-stage self-seeding scheme of LCLS-II. 		 
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2018-THPMK053  
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THPMK054 Analysis of 1D FEL Sideband Instability with Inclusion of Energy Detune and Space Charge 4410
 
  • C.-Y. Tsai, J. Wu, C. Yang, G. Zhou
    SLAC, Menlo Park, California, USA
  • M. Yoon
    POSTECH, Pohang, Kyungbuk, Republic of Korea
  
  Funding: The work was supported by the US Department of Energy (DOE) under contract DE- AC02-76SF00515 and the US DOE Office of Science Early Career Research Program grant FWP-2013-SLAC-100164.
It has been known that free-electron laser (FEL) is capable of generating a coherent high-power radiation over a broad spectrum. Recently there is a great interest in pursuing higher peak power (for example, at terawatt level) in FEL that can enable coherent diffraction imaging and probe fundamental high-field physics. The FEL radiation power can be increased by virtue of undulator tapering. However the FEL sideband signal begins to exponentially grow in the post-saturation regime. In this paper we extend our sideband analysis* by including both the energy detune due to discrete undulator tapering and longitudinal space charge in an effective 1-D model. A dispersion relation with explicit energy detune and space charge is derived. The study is carried out semi-analytically and compared with simulations. The impact of energy detune and space charge is analyzed.
* C.-Y. Tsai et al., Analysis of the sideband instability based on a one-dimensional high-gain free electron laser model, PRAB (accepted) 		 
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2018-THPMK054  
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THPMK055 Self Seeding Scheme for LCLS-II-HE 4414
 
  • C. Yang, Y. Feng, J. Krzywinski, T.O. Raubenheimer, C.-Y. Tsai, J. Wu, M. Yoon, G. Zhou
    SLAC, Menlo Park, California, USA
  • H.X. Deng, X.F. Wang
    SINAP, Shanghai, People's Republic of China
  • D.H. He
    USTC/NSRL, Hefei, Anhui, People's Republic of China
  • Y. Hong, B. Yang
    University of Texas at Arlington, Arlington, USA
  • M. Yoon
    POSTECH, Pohang, Kyungbuk, Republic of Korea
  • G. Zhou
    IHEP, Beijing, People's Republic of China
  
  Funding: The work was supported by the US Department of Energy (DOE) under contract DE-AC02-76SF00515 and the US DOE Office of Science Early Career Research Program grant FWP-2013-SLAC-100164.
Self-seeding is a reliable approach to generate fully coherent FEL pulses. Hard X-ray self-seeding can be realized by using a single crystal in Bragg transmission geometry. However, for a high repetition rate machine, the heat load on the crystal may become an issue. In this paper, we will study the facility performance of LCLS-II-HE by numerical simulations, and discuss the heat load and optimal undulator baseline configuration of LCLS-II-HE self-seeding scheme, and study the emittance tolerance of the LCLS-II-HE. 		 
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2018-THPMK055  
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THPMK056 Effect of Transverse Radiation Defocusing in Post-Saturation Regime of High-Gain X-Ray Free-Electron Laser 4418
 
  • C.-Y. Tsai, J. Wu, C. Yang, G. Zhou
    SLAC, Menlo Park, California, USA
  • M. Yoon
    POSTECH, Pohang, Kyungbuk, Republic of Korea
  • G. Zhou
    IHEP, Beijing, People's Republic of China
  
  Funding: The work was supported by the US Department of Energy (DOE) under contract DE- AC02-76SF00515 and the US DOE Office of Science Early Career Research Program grant FWP-2013-SLAC-100164.
When untapered high-gain free electron laser (FEL) reaches saturation, the exponential growth ceases and the radiation power starts to oscillate about an equilibrium. For a high-gain tapered FEL, although the power is enhanced after the first saturation, it is known that there is a so-called second saturation point where the FEL power growth stops. In addition to the sideband instability, lack of transverse radiation focusing in the post-saturation regime can be another major reason leading to occurrence of the second saturation. In this paper we study the transverse diffraction effect and its impact on tapered FEL in the post-saturation regime. The study is carried out analytically together with three-dimensional numerical simulation. The numerical parameters are taken from LCLS-like electron beam and undulator system. 		 
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2018-THPMK056  
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THPMK059 Commissioning of Front End of CLARA Facility at Daresbury Laboratory 4426
 
  • D. Angal-Kalinin, A.D. Brynes, R.K. Buckley, S.R. Buckley, J.A. Clarke, L.S. Cowie, K.D. Dumbell, D.J. Dunning, B.D. Fell, P. Goudket, A.R. Goulden, S.A. Griffiths, F. Jackson, S.P. Jamison, J.K. Jones, P.A. McIntosh, J.W. McKenzie, K.J. Middleman, B.L. Militsyn, A.J. Moss, B.D. Muratori, T.C.Q. Noakes, T.J. Price, M.D. Roper, Y.M. Saveliev, D.J. Scott, B.J.A. Shepherd, R.J. Smith, E.W. Snedden, N. Thompson, C. Tollervey, R. Valizadeh, D.A. Walsh, T.M. Weston, A.E. Wheelhouse, P.H. Williams
    STFC/DL/ASTeC, Daresbury, Warrington, Cheshire, United Kingdom
  • A.D. Brynes, J.A. Clarke, L.S. Cowie, K.D. Dumbell, D.J. Dunning, P. Goudket, F. Jackson, S.P. Jamison, J.K. Jones, P.A. McIntosh, J.W. McKenzie, K.J. Middleman, B.L. Militsyn, A.J. Moss, B.D. Muratori, Y.M. Saveliev, D.J. Scott, B.J.A. Shepherd, N. Thompson, R. Valizadeh, A.E. Wheelhouse, P.H. Williams
    Cockcroft Institute, Warrington, Cheshire, United Kingdom
  • R.J. Cash, R.F. Clarke, G. Cox, G.P. Diakun, A. Gallagher, K.D. Gleave, M.D. Hancock, J.P. Hindley, C. Hodgkinson, A. Oates, J.T.G. Wilson
    STFC/DL, Daresbury, Warrington, Cheshire, United Kingdom
  
  CLARA (Compact Linear Accelerator for Research and Applications) is a Free Electron Laser (FEL) test facility being developed at STFC Daresbury Laboratory. The principal aim of CLARA is to test advanced FEL schemes which can later be implemented on existing and future short wavelength FELs. The installation of the Front End (FE) section of CLARA, a S-bend merging with existing VELA (Versatile Electron Linear Accelerator) beam line and installation of a high repetition rate RF gun on VELA was completed in 2017. First beam commissioning results and high level software developments are presented in this paper.  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2018-THPMK059  
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THPMK060 Start-to-End Simulations of the CLARA FEL Test Facility 4430
 
  • D.J. Dunning, D. Angal-Kalinin, A.D. Brynes, L.T. Campbell, H.M. Castaneda Cortes, J.K. Jones, J.W. McKenzie, N. Thompson, P.H. Williams
    STFC/DL/ASTeC, Daresbury, Warrington, Cheshire, United Kingdom
  • D. Angal-Kalinin, A.D. Brynes, D.J. Dunning, J.K. Jones, J.W. McKenzie, B.W.J. MᶜNeil, N. Thompson, P.H. Williams
    Cockcroft Institute, Warrington, Cheshire, United Kingdom
  • L.T. Campbell, B.W.J. MᶜNeil, P.T. Traczykowski
    USTRAT/SUPA, Glasgow, United Kingdom
  • B.S. Kyle
    University of Manchester, Manchester, United Kingdom
  • B.S. Kyle
    UMAN, Manchester, United Kingdom
  • J.D.A. Smith
    TXUK, Warrington, United Kingdom
  
  CLARA is a new FEL test facility being developed at STFC Daresbury Laboratory in the UK, aiming to deliver advanced FEL capabilities including few-cycle pulse generation and Fourier transform limited output. Commissioning is underway on the front-end (photo-injector and first linac) while the later stages are being procured and assembled. Start-to-end (S2E) simulations of the full facility are presented, including optimisation of the accelerator setup to deliver the required properties of one of the electron beam modes specified for FEL operation. FEL simulations are performed using the Genesis 1.3 and Puffin codes and the results are compared.  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2018-THPMK060  
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THPMK061 Isolated Few-Cycle Pulse Generation in X-Ray Free-Electron Lasers 4434
 
  • D.J. Dunning, L.T. Campbell, N. Thompson
    STFC/DL/ASTeC, Daresbury, Warrington, Cheshire, United Kingdom
  • L.T. Campbell, B.W.J. MᶜNeil
    USTRAT/SUPA, Glasgow, United Kingdom
  • D.J. Dunning, B.W.J. MᶜNeil, N. Thompson
    Cockcroft Institute, Warrington, Cheshire, United Kingdom
  • J.D.A. Smith
    TXUK, Warrington, United Kingdom
  
  X-ray free-electron lasers are promising candidates to deliver high-brightness radiation pulses with duration significantly shorter than the present leading technique, high harmonic generation (HHG). This would extend attosecond science to probe ultrafast dynamics with even finer resolution. To do so requires breaking below a characteristic FEL timescale of typically a few hundred optical cycles, dictated by the relative slippage of the radiation and electrons during amplification. The concept of mode-locking enables this, with the mode-locked afterburner configuration predicted to deliver few-cycle pulses (~ 1 attosecond at hard X-ray). However such techniques would produce a train of closely separated pulses, while an isolated pulse would be preferable for some types of experiment. Building on previous techniques, a new concept has been developed for isolated few-cycle pulse generation and it is presented alongside simulation studies.  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2018-THPMK061  
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THPMK064 RF System for SXFEL: C-band, X-band and S-band 4446
 
  • W. Fang, Q. Gu, X.X. Huang, L. Li, Z.B. Li, J.H. Tan, C.C. Xiao, J.Q. Zhang, Z.T. Zhao
    SINAP, Shanghai, People's Republic of China
  
  Shanghai Soft X-ray FEL facility is under commissioning now, which linac is compased of one S-band injector, C-band main linac and X-band linearizer. In SXFEL S-band injector could provide 200MeV beam energy based on 4 RF power unit, and then 6 C-band RF units boost beam energy to 840MeV based on 33MV/m at least, which will be ramped to 40MV/m in the ungrading. In the middle of S-band and C-band RF system, a X-band RF unit is used as linearizer to make energy spread of electron beam linear distribution, which is important for bunch compressor and FEL radiation. In this paper, details of RF system design and status of SXFEL is introduced, and some operation results are presented.  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2018-THPMK064  
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THPMK068 High degree circular polarization at x-ray self-seeding FELs with crossed-planar undulators 4453
 
  • K. Li, H.X. Deng, Z.F. Gao, B. Liu, D. Wang
    SINAP, Shanghai, People's Republic of China
  
  Funding: Work was supported by the National Natural Science Foundation of China (11775293), the National Key Research and Development Program of China (2016YFA0401900).
The crossed undulator configuration for a high-gain free-electron laser (FEL) is well-known for the ability of versatile polarization control. However, the degree of polarization is very sensitive to power and phase between the two stages of crossed undulators. In this poster, we introduce the generation of high degree circular polarization hard x-ray FEL with crossed-planar undulator seeded by self-seeding. The reverse taper and taper undulator technology are employed for improving its performance. With the combination of high degree (>95%) circular polarization and flexibility of polarization switching, this scheme might be useful for some scientific research in the future. 		 
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2018-THPMK068  
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THPMK069 Design of the Beam Switchyard of a Soft X-ray FEL User Facility in Shanghai 4456
 
  • S. Chen, H.X. Deng, C. Feng, B. Liu, D. Wang, R. Wang
    SINAP, Shanghai, People's Republic of China
  
  A soft X-ray FEL user facility, which is based on the existing test facility located in the Zhangjiang Campus of SINAP, is under construction. Two undulator lines will be installed parallelly in the undulator hall and their electron beams are served by a 1.5 GeV linac. For simultaneous operation of the two undulator lines, a beam distribution system should be used to connect the linac and the undulator lines. In this paper, the physics design of this beam distribution system will be presented and also the beam dynamic issues will be discussed.  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2018-THPMK069  
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THPMK070 Optimization for the Two-Stage Hard X-Ray Self-Seeding Scheme the SCLF 4460
 
  • T. Liu, C. Feng, D. Wang, X. Wang, K.Q. Zhang
    SINAP, Shanghai, People's Republic of China
  
  Funding: Work supported by the National Natural Science Foundation of China 11475250 and 11605277, National Key Research and Development 2016YFA0401901 and Youth Innovation Promotion Association CAS 2015209.
Self-seeding mode has been demonstrated a great advantage for the achievement of a high brightness X-ray with a pure spectrum. Single-bunch self-seeding scheme with wake monochromators is adopted for the realization of the hard X-ray FEL at the Shanghai Coherent Light Facility (SCLF). Limited by the heat-loading of the monochromator, the two or multiple stages self-seeding scheme is required. In this contribution, we present a basic two-stage scheme design and optimization for the generation of the photon energy range of 3 keV to 15 keV at the line FEL-I of the SCLF. Simulation results show the peak power and pulse energy each stage, which illustrates the loaded energy required of the crystal monochromator as a pointcut of its following thermal analysis. The electron beam energy used in the study is 8 GeV and the central photon energy is 12.4 keV. 		 
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2018-THPMK070  
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THPMK072 X-Band RF System as Linearizer for SXFEL 4467
 
  • J.H. Tan, W. Fang, Q. Gu, X.X. Huang, Z.T. Zhao
    SINAP, Shanghai, People's Republic of China
  
  High gradient accelerating structure is the core technology of compact linear collider facilities and compact free electron laser facilities. Meanwhile the important limitation of improving brightness in free electron laser facility is the non-linear energy spread, and the X-band accelerating structure can provide harmonic compensation in linac to linearize the bunch compression process. In this paper, a special X-band traveling-wave accelerating structure is primary designed for compact hard x-ray free electron laser facility. Then the structure is processed manufacturing, and realize high power experiment and linear bunch compression at Shanghai soft x-ray free electron laser facility.  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2018-THPMK072  
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THPMK077 The Preliminary Experiment Studies for Soft X-Ray Self-Seeding System Design of SCLF Facility 4481
 
  • K.Q. Zhang, C. Feng, D. Wang, Z.T. Zhao
    SINAP, Shanghai, People's Republic of China
  
  The preliminary experiment studies for soft x-ray self-seeding system design of SCLF facility have been pre-sented in this paper. Some practical problems and pre-engineering design have been studied for the experimental prepare of soft x-ray self-seeding for the future SCLF facility. The monochromator system designs in this paper include optical structure, optical parameters and mechanical design. The designed optical system has an optical resolution of 1/10000 at the photon energy of 700-1300eV based on the optical simulation. To make the system satisfy the experimental requirements, mechanical install requirements and install precisions are also analysed. Considering the actual varies errors, the errors analyses such as the surface errors of the optical mirror and the machining errors of the VLS grating are also carried out. In conclusion, preliminary experimental studies including system design and varies engineering requirements are introduced to make sure that the presented design is reliable for final soft x-ray self-seeding experiment of SCLF facility.  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2018-THPMK077  
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THPMK078 Corrugated Structure as a Linearizer in High Repetition Rate X-Ray Free Electron Laser Source 4485
 
  • Z. Wang, C. Feng, D. Huang, K.Q. Zhang, M. Zhang
    SINAP, Shanghai, People's Republic of China
  
  A feasible method is proposed to compensate the high order mode (HOM) of the RF field, linearize the bunch compression process in the high repetition rate x-ray free electron laser source. In the proposed scheme, the corrugated structure is used in the superconducting linac to linearize the longitudinal phase space of the electron beam. The results show that the peak current of the electron beam will be increased from about 1 kA to over 2 kA with the charge of 100 pC.  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2018-THPMK078  
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THPMK082 Micro Bunch Rotation and Coherent Undulator Radiation From a Kicked Beam 4489
SUSPF013   use link to see paper's listing under its alternate paper code  
 
  • J.P. MacArthur
    Stanford University, Stanford, California, USA
  • Z. Huang, J. Krzywinski, A.A. Lutman
    SLAC, Menlo Park, California, USA
  
  Recent observations of x-rays from a microbunched beam that has been kicked off-axis have shown coherent radiation at surprisingly large angles, in some cases reaching 30-50 uRad. Previous work on the topic has suggested that radiation at such large angles is inconsistent with classical radiation theory because microbunches cannot tilt. Here we show that, when kicked in a quadrupole lattice, microbunches can automatically tilt toward a new direction of propagation. This allows for coherent radiation farther off axis.  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2018-THPMK082  
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THPMK083 Self-Modulation of a Relativistic Electron Beam in a Wiggler 4492
 
  • J.P. MacArthur
    Stanford University, Stanford, California, USA
  • J.P. Duris, Z. Huang, A. Marinelli, Z. Zhang
    SLAC, Menlo Park, California, USA
  
  Users at x-ray free-electron laser (FEL) facilities have shown strong interest in using single spike, coherent x-ray pulses to probe attosceond dynamics in atoms and molecules. Sub-femtosecond soft x-ray pulses may be obtained from an electron beam that has been modulated in a wiggler resonant with an external laser, the enhanced-SASE technique. We discuss a new way to produce this energy modulation, wherein the external laser is replaced by coherent radiation from the current spike on the tail of the electron beam. We calculate the modulation expected in a wiggler from both a single frequency perspective and a coherent synchrotron radiation (CSR) perspective.  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2018-THPMK083  
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THPMK112 An Updated Description of the FEL Simulation Code Puffin 4579
 
  • L.T. Campbell, B.W.J. MᶜNeil, P.T. Traczykowski
    USTRAT/SUPA, Glasgow, United Kingdom
  • L.T. Campbell
    STFC/DL/ASTeC, Daresbury, Warrington, Cheshire, United Kingdom
  • B.W.J. MᶜNeil
    Cockcroft Institute, Warrington, Cheshire, United Kingdom
  • J.D.A. Smith
    TXUK, Warrington, United Kingdom
  
  Puffin [1] is an unaveraged 3D FEL simulation tool with no Slowly Varying Envelope Approximation (SVEA), no undulator period averaging of the electron motion, and no periodic slicing of the electron beam, enabling simulation of broadband and high resolution FEL phenomena. It is a massively parallel code, written in modern Fortran and MPI, which scales from single core machines to HPC facilities. Its use in a number of projects since its initial description in 2012 has necessitated a number of additions to expand or improve its capability, including new numerical techniques, and the addition of a wide and flexible array of undulator tunings and polarizations along with electron beam optics elements for the undulator line. In the following paper, we provide an updated description of Puffin including an overview of these updates.
[1] L.T. Campbell and B.W.J. McNeil, Phys. Plasmas 19 093119 (2012) 		 
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2018-THPMK112  
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THPMK124 The Radiation Source for a Pre-Bunched THz Free Electron Laser 4608
 
  • R. Huang, Z.G. He, Q.K. Jia, H.T. Li, W.W. Li, Y. Lu, L. Wang, Z. Zhao
    USTC/NSRL, Hefei, Anhui, People's Republic of China
  
  Funding: Work is supported by National Natural Science Foundation of China (Grant No. 51627901)
Electron beam, generated in a photoinjector and bunched at terahertz (THz) frequency, will excite the coherent THz radiation when entering an undulator. We present a scheme of the radiation source for the pre-bunched THz free electron laser (FEL). The physical design of electron source is described in detail. The radiation frequency is widely tunable by both the pulse train tuning and the undulator gap tuning. It is simulation proved that the radiation power is greatly enhanced in our scheme. 		 
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2018-THPMK124  
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THPMK127 Terahertz Smith-Purcell Radiation From the High-Harmonic Component of Modulated Electron Beam From Dielectric Structure 4617
 
  • S.M. Jiang, Z.G. He, Q.K. Jia, W.W. Li, L. Wang
    USTC/NSRL, Hefei, Anhui, People's Republic of China
  • D. He
    Anhui Electrical Engineering Professional Technique College, Hefei, People's Republic of China
  
  Funding: Supported by National Nature Science Foundation of China(11705198, 11775216)
In this paper, a new radiation scheme, which adopts the high order harmonic of modulated electron beam from dielectric loaded waveguide to excite the Smith-Purcell terahertz (THz) radiation, is proposed and in-vestigated by numerical simulations. The results show that the radiation with frequency close to 1.0 THz is generated, while, the fundamental bunching frequency of electron beam is 0.28 THz. Thus, this scheme offer a new method to get the higher frequency THz radiation. 		 
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2018-THPMK127  
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THPMK138 Power Enhancement of Free-Electron Lasers Oscillators With the Natural Gradient of a Planar Undulators 4632
SUSPF012   use link to see paper's listing under its alternate paper code  
 
  • Z. Zhao, L.J. Chen, Q.K. Jia, H.T. Li
    USTC/NSRL, Hefei, Anhui, People's Republic of China
  
  Funding: Work supported by National Natural Science Foundation of China (No. 21327901, 11205156)
Transverse Gradient Undulator (TGU) has been proposed with the initial purpose of mitigating the gain degradation in free electron laser (FEL) oscillators driven by beams with a large energy spread. However, a special-designed TGU with a fixed transverse gradient is required to enhance the gain. In this paper, we investigate using the natural field gradient of a normal planar undulator instead of a TGU to enhance the FEL oscillator (FELO) power. In this method, the beam is first vertically dispersed by a dogleg and then the dispersed beam passes through a normal undulator with a vertical off-axis orbit. Theoretical analysis and numerical simulation based on parameters of FELiChEM are presented. It demonstrates that this scheme can enhance the FEL power with careful optimization of dispersion strength and vertical beam orbit offset, especially when the energy spread is relatively large. 		 
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2018-THPMK138  
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FRYGB1
 Review of FEL Science  
 
  • J. Yano
    LBNL, Berkeley, California, USA
  
  This invited talk will present a review of recent scientific highlights from X-ray FELs covering a broad range of disciplines including Structural Biology, Atomic and Molecular Physics, Photochemistry, Non-linear Spectroscopy, Shock Physics, and Solid Density Plasmas. The science achievements to date from these unique photon sources are already shaping our future.  
slides icon Slides FRYGB1 [63.266 MB]  
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