IPAC2018 - List of Keywords (FEL)

Paper	Title	Other Keywords	Page
MOZGBD1	Towards Full Performance Operation of SwissFEL	experiment, photon, electron, laser	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 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	photon, MMI, undulator, electron	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 MOZGBD2 [18.822 MB]
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2018-MOZGBD2
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MOZGBD5	A Proposal for Coherent Hard X-Ray Generation Based on Two-Stage EEHG	electron, laser, linac, radiation	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 MOZGBD5 [7.330 MB]
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2018-MOZGBD5
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MOPMF044	New Coordination Tools to Prepare Programmed Stops in the LHC and its Injectors	simulation, hardware, MMI, dipole	200
	S. Chemli, M. Bernardini, T.W. Birtwistle, A. Bolognesi, B. Brito Da Palma, S.E. Bustamante, J. Coupard, K. Foraz, E. Kleszcz, N. Kotsolakos, T. Krastev, P. A. Kulig, Y. Muttoni, B. Nicquevert, L. Pater, A. Patrascoiu, S. Petit, C. Rauser, A. Wardzinska CERN, Geneva, Switzerland
	The LHC and its Injectors are submitted to an overall lifecycle of three to four years of physics delivery to Experiments with a two-year long stop, also known as Long Shutdown (LS). The years of physics delivery are ended by a programmed stop for the immediate preventive and corrective maintenance, also known as (Extended)-Year-End Technical Stop - (E)YETS. This regular cycle is to be addressed in parallel with other projects: the upgrade projects to the accelerator complex of the LHC (High-Luminosity project) and to its Injectors (LHC Injectors Upgrade), and the "standard" consolidation tasks. This paper describes the way the programmed stops coordination group prepares the activities to take place during the stop with a set of new tools and processes that ease the communication between the stakeholders of the coordination.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2018-MOPMF044
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MOPML047	Diversified Application of ILC	photon, neutron, scattering, electron	502
	Y. Iwashita Kyoto ICR, Uji, Kyoto, Japan T. Hayakawa QST, Tokai, Japan N. Kawamura, S. Makimura, K. Mishima, D. Nomura, K. Shimomura, S. Yamamoto, T. Yamazaki KEK, Ibaraki, Japan
	ILC will be a very powerful accelerator complex. It has not only the high power energetic electron beam but also positron and photon beams. In addition to these beams, large cryogenic plants are equipped together with various utility facilities. Some suggestions on the assumption of availability of ILC are offered from various fields. These discussions will be reported.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2018-MOPML047
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MOPML068	Training the Next Generation of Accelerator Experts	network, laser, electron, synchrotron	564
	C.P. Welsch The University of Liverpool, Liverpool, United Kingdom C.P. Welsch Cockcroft Institute, Warrington, Cheshire, United Kingdom
	Funding: Work supported by the European Union under grant agreements no 215080, 289191, 289485, 675265 and 721559. Close collaboration between academia, research centres and industry has turned out to be crucial for the advancement of accelerator science and technology. It is also ideal for providing an efficient training of the next generation of particle accelerator experts and for linking the global accelerator community. Five international research and training networks (DITANET, oPAC, LA3NET, OMA and AVA) have been initiated and coordinated by the University of Liverpool/Cockcroft Institute since 2007. These networks have provided training to almost 100 Fellows from all over the world and organised dozens of international schools, topical workshops and international conferences for the accelerator community. The research activities of the networks have led to hundreds of journal publications and conference proceedings. This contribution presents the best practice in establishing such international collaborative projects, how to establish successful links between sectors and countries, and highlights the main research results that resulted from the research programs.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2018-MOPML068
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MOPML069	Enhancing Hadron Therapy through OMA	proton, simulation, medical-accelerators, hadron	568
	C.P. Welsch The University of Liverpool, Liverpool, United Kingdom C.P. Welsch Cockcroft Institute, Warrington, Cheshire, United Kingdom
	Funding: This project has received funding from the European Union's Horizon 2020 research and innovation programme under the Marie SkłodowskaCurie grant agreement No 675265. Continued research into the optimization of medical accelerators is urgently required to assure the best possible cancer care for patients and this is one of the central aims of the OMA project which received 4 M€ of funding from the European Commission. A consortium of universities, research and clinical facilities, as well as partners from industry carry out an interdisciplinary R&D program across three closely interlinked scientific work packages. These address the development of novel beam imaging and diagnostics systems, studies into treatment optimization including innovative schemes for beam delivery and enhanced biological and physical models in Monte Carlo codes, as well as R&D into clinical facility design and optimization to ensure optimum patient treatment along with maximum efficiency. Selected research highlights from across these work packages will be presented and the impact on hadron therapy facilities around the world discussed.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2018-MOPML069
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TUXGBF2	Higher-Order-Mode Effects in Tesla-Type Superconducting RF Cavities on Electron Beam Quality	HOM, cavity, electron, detector	612
	A.H. Lumpkin, N. Eddy, D.R. Edstrom, P.S. Prieto, J. Ruan, R.M. Thurman-Keup Fermilab, Batavia, Illinois, USA K. Bishofberger, B.E. Carlsten LANL, Los Alamos, New Mexico, USA O. Napoly CEA/DSM/IRFU, France
	Funding: Work at Fermilab supported by FRA, LLC under Contract No. DE-AC02-07CH11359 with the U.S. Dept. of Energy. *Work at LANL supported by U.S. Dept. of Energy through the LANL/LDRD Program. We report the direct observations of the correlation of higher order modes (HOMs) generated by off-axis electron beam steering in TESLA-type SCRF cavities and sub-macropulse beam centroid shifts (with the concomitant effect on averaged beam size and emittance). The experiments were performed at the Fermilab Accelerator Science and Technology (FAST) facility using its unique configuration of a PC rf gun injecting beam into two separated 9-cell cavities in series with corrector magnets and beam position monitors (BPMs) located before, between, and after them. The ~100-kHz oscillations with up to 300-μm amplitudes at downstream locations were observed in a 3-MHz micropulse repetition rate beam with charges of 500 and 1000 pC/b, although the effects were much reduced at 100 pC/b. The studies were based on HOM detector circuitry targeting the first and second dipole passbands, rf BPM bunch-by-bunch data, and imaging cameras viewing multi-slit images for emittance assessments at 33 MeV. Initial calculations reproduced a key feature of the phenomena. In principle, these results may be scaled to cryomodule configurations of major accelerator facilities.
	Slides TUXGBF2 [3.631 MB]
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2018-TUXGBF2
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TUPAL067	Accelerators Validating Antimatter Physics	proton, antiproton, experiment, electron	1167
	C.P. Welsch The University of Liverpool, Liverpool, United Kingdom C.P. Welsch Cockcroft Institute, Warrington, Cheshire, United Kingdom
	Funding: This project has received funding from the European Union's Horizon 2020 research and innovation programme under the Marie Skłodowska-Curie grant agreement No 721559. The Extra Low Energy Antiproton ring (ELENA) will be a critical upgrade to the unique Antiproton Decelerator facility at CERN and is currently being commissioned. ELENA will significantly enhance the achievable beam quality and enable new experiments. To fully exploit the discovery potential of this facility, advances are urgently required in numerical tools that can adequately model beam transport, life time and interaction, beam diagnostics tools and detectors to fully characterize the beam's properties, as well as in novel experiments that exploit the enhanced beam quality that ELENA will provide. These three areas form the scientific work packages of the new pan-European research and training initiative AVA (Accelerators Validating Antimatter physics). The project has received around 4M€ of funding and brings together universities, research centers and industry to train 15 Fellows through research in this area. This contribution presents the research results across AVA's three scientific work packages.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2018-TUPAL067
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TUPMF044	First Lasing of the CAEP THz FEL Facility Driven by a Superconducting Accelerator	laser, electron, free-electron-laser, undulator	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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TUPMF069	Low Gain FEL Oscillator Option for PETRA IV	undulator, emittance, storage-ring, electron	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	electron, simulation, photon, laser	1440
	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	laser, experiment, electron, simulation	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	electron, laser, undulator, radiation	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	cavity, operation, controls, accelerating-gradient	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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TUPMF085	Status of the sFLASH Experiment	electron, laser, photon, 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	undulator, laser, optics, electron	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.
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TUPMF090	Status of the Superconducting Soft X-Ray Free-Electron Laser FLASH at DESY	laser, operation, undulator, electron	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.
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TUPMK009	Electron Beam Optics for the ASU Compact XFEL	dipole, simulation, electron, laser	1507
	C. Zhang, W.S. Graves, M.R. Holl, L.E. Malin Arizona State University, Tempe, USA E.A. Nanni SLAC, Menlo Park, California, USA
	Funding: National Science Foundation Division of Physics (Accelerator Science) award 1632780, award 1231306. DOE grant DE-AC02-76SF00515. Arizona State University (ASU) is pursuing a new concept for a compact x-ray FEL (CXFEL) as a next phase of compact x-ray light source (CXLS). We describe the electron beam optics design for the ASU compact XFEL. In previous experiments we introduced a grating diffraction method to generate a spatially modulated beam. We plan to combine a telescope imaging system with emittance exchange (EEX) to magnify/demagnify the modulated beam and transfer it from transverse modulation into a longitudinal one to make it an ideal seed for phase-coherent XFEL. The simulation results of the beam line setup will be demonstrated. Our first goal is to successfully image the modulated beam with desired magnification then we will investigate various magnification and magnets combinations and optimize aberration correction.
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TUPML011	Experiments Producing Nanopatterned Electron Beams	electron, bunching, experiment, emittance	1553
	L.E. Malin, W.S. Graves, J. Spence, K. Weiss, C. Zhang Arizona State University, Tempe, USA R.K. Li, E.A. Nanni, X. Shen, S.P. Weathersby, J. Yang SLAC, Menlo Park, California, USA
	Funding: Work supported by NSF awards 1632780 and 1231306, DOE award DE-AC02-76SF00515, and the SLAC UED/UEM Initiative Program Development Fund. RF photoinjectors are increasingly used to image at the nanoscale in much the same way as a Transmission Electron Microscope (TEM), which are generally sub-MeV energy. We have conducted electron diffraction experiments through a thin membrane of single crystal silicon using both the TEM and photoinjector, and have been able to model and predict the diffraction patterns using the multislice method. A nanopatterned single crystal silicon grating was also imaged in the TEM in the bright field, where all but the direct beam of the diffraction pattern is blocked, giving high contrast spatial modulations corresponding to the 400 nm pitch grating lithographically etched into the silicon. Drawing from our previous multislice calculations, we determined the crystallographic orientation that maximized the contrast in this spatial modulation at the energy of the TEM, giving a bunching factor comparable to a saturated FEL. We report on these key steps toward control of radiation phase and temporal coherence in an FEL.
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TUPML019	Design of Multi-Alkali Photocathode Preparation System for CTFEL Facility	cathode, vacuum, laser, electron	1571
	D.X. Xiao, M. Li, Q. Pan, H. Wang, X. Yang CAEP/IAE, Mianyang, Sichuan, People's Republic of China
	The first saturated lasing of the China Academy of Engineering Physics tera-hertz free electron laser (CTFEL) facility has been realized. In order to improve the performance of the CTFEL facility, the multi-alkali photocathode with much longer life-time has been proposed to replace the GaAs photocathode currently used. This paper presents the design of the multi-alkali photocathode preparation system, which consists of three chambers: the suitcase chamber, the preparation chamber, and the loading chamber. The function of each chamber is also discussed.
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TUPML035	FELs Driven by Laser Plasma Accelerators Operated with Transverse Gradient Undulators	undulator, electron, radiation, laser	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
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WEXGBD2	Pulse-by-Pulse Multi-XFEL Beamline Operation with Ultra-Short Laser Pulses	electron, optics, operation, undulator	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 WEXGBD2 [9.708 MB]
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2018-WEXGBD2
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WEYGBD2	Status of the Radiation Damage on the European XFEL Undulator Systems	undulator, radiation, operation, electron	1776
	F. Wolff-Fabris, J. Pflüger XFEL. EU, Schenefeld, Germany F. Hellberg Stockholm University, Stockholm, Sweden F. Schmidt-Föhre DESY, Hamburg, Germany
	The European XFEL GmbH is a new X-ray FEL user facility and started lasing in 2017. Three gap movable SASE Undulator Systems are designed to produce FELs with tunable wavelengths from 0.05 to 5.2nm [,]. A total of 91 5-m long undulator segments based on hybrid NdFeB permanent magnet technology were tuned respecting tight specifications. Radiation damage due to machine operation affects the magnetic properties of the segments and the quality of the SASE process. An array of dosimeters based on Radfets [*] and Gafchromic films monitors the absorbed doses in every undulator segment and each SASE system is equipped with a 12mm gap diagnostic undulator (DU) which is magnetically re-measured during machine maintenance weeks. Doses up to 4 kGy have been observed and magnetic field degradation higher than 3% is measured. These results permit to estimate the effects of radiation damage and life expectancy of the Undulator Systems based on the precise K-parameter determination for beam operation. We will present the results of magnetic re-measurements on the Undulator Systems, the details of the effects of radiation damage and future plans to maximize the beam quality and operation. M. Altarelli et al., Tech. Design Rep. DESY 2006-097, July 2007. E. Schneidmiller et al., Eur. XFEL Tech. Rep. TR-2011-006, Sep. 2011. * F. Schmidt-Föhre et al., IPAC-2018 contribution.
	Slides WEYGBD2 [3.670 MB]
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2018-WEYGBD2
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WEYGBE2	Applications of Caustic Methods to Longitudinal Phase Space Manipulation	electron, linac, optics, gun	1790
	T.K. Charles The University of Melbourne, Melbourne, Victoria, Australia T.K. Charles CERN, Geneva, Switzerland D. Douglas JLab, Newport News, Virginia, USA P.H. Williams STFC/DL/ASTeC, Daresbury, Warrington, Cheshire, United Kingdom
	Longitudinal phase space management is a key feature of recirculating machines. Careful consideration of the longitudinal matching is required not only in order to ensure a high peak current, low energy spread bunch is delivered to the FEL but also to support the deceleration and energy recovery of the spent beam. In a similar manner, longitudinal phase space manipulation can be utilised for pulse shaping in bunch compression, to minimise the influence of CSR-induced emittance growth. In this paper, we present a method for longitudinal phase space matching based upon the avoidance of electron trajectory caustics. Through considering the conditions under which caustics will form, we generate exclusion plots identifying the viable parameter space at numerous positions through beam acceleration and energy recovery. The result is a method for selecting the linear momentum compaction and the higher-order momentum compaction to satisfy the non-caustic condition whilst achieving the bunch compression or lengthening as required.
	Slides WEYGBE2 [6.292 MB]
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WEPAF027	Low Q Cavity BPM Study for the Beam Position Measurement of Nanosecond Spaced Electron Bunches	cavity, dipole, electron, coupling	1881
	L. Yang, X. He, L.W. Zhang CAEP/IFP, Mainyang, Sichuan, People's Republic of China S.S. Cao, Y.B. Leng, L.Y. Yu, R.X. Yuan SINAP, Shanghai, People's Republic of China
	Funding: National natural science foundation of China, 11705184 Low Q cavity BPM is a key to distinguish closely spaced electron bunches allowing precise beam handling for XFEL facilities operating in a multi-bunch mode at high repetition rate up to hundreds MHz. The inter-bunch signal pollution issue becomes significant when bunch separation is down to nanosecond and causes the position detection to be increasingly overestimated. Solely relying on extreme low Q to achieve sufficient decay within bunch interval leads to appreciable interference from non-signal modes due to strong overcoupling of antenna design is required. The error imposed on measured position raises a challenge to meet the goal of high resolution. Alternatively, a concept is proposed to remove the dominant part of signal pollution at the moment of sampling by intentionally shifting the phase of the last bunch signal 90degree respect to that of current bunch signal, where signal sampling is normally taken for nanosecond spaced bunches. This quadrature phase shift is defined by properly choosing the operational frequency of dipole mode regarding to the bunch frequency. A low Q cavity BPM prototype to identify technical challenges and verify this concept is under development in the R&D plan for future XFEL with high repetition rate
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WEPAF035	Coherent Diffraction Radiation Imaging as an RMS Bunch Length Monitor	radiation, target, experiment, detector	1895
	J. Wolfenden, R.B. Fiorito, C.P. Welsch Cockcroft Institute, Warrington, Cheshire, United Kingdom R.B. Fiorito, C.P. Welsch, J. Wolfenden The University of Liverpool, Liverpool, United Kingdom T.H. Pacey, T.H. Pacey UMAN, Manchester, United Kingdom A.G. Shkvarunets UMD, College Park, Maryland, USA
	Funding: This work was supported by the EU under Grant Agreement No. 624890 and the STFC Cockcroft Institute core Grant No. ST/G008248/1. High-resolution bunch length measurement is of the utmost importance for current and future generations of light sources and linacs. It is also key to the optimisation of the final beam quality in plasma-based acceleration. We present progress in the development of a novel RMS bunch length monitor based on imaging the coherent diffraction radiation (CDR) produced by a non-invasive circular aperture. Due to the bunch lengths involved, the radiation produced is in the THz range. This has led to the development of a novel THz imaging system, which can be applied to low energy electron beams. For high energy beams the imaging system can be used as a single shot technique. Simulation results show that the profile of a CDR image of a beam is sensitive to bunch length and can thus be used as a diagnostic. The associated benefits of this imaging distribution methodology over the typical angular distribution measurement are discussed. Plans for experiments conducted at the SwissFEL (PSI, Switzerland), along with plans for future high energy single shot measurements are also presented.
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WEPAF047	Status and Commissioning of the Wire Scanner System for the European XFEL	detector, undulator, MMI, emittance	1919
	T. Lensch, S. Liu DESY, Hamburg, Germany
	The European-XFEL (E-XFEL) is an X-ray Free Electron Laser facility located in Hamburg (Germany). The superconducting accelerator for up to 17.5 GeV electrons will provide photons simultaneously to several user stations. Currently 12 Wire Scanner stations are used to image transverse beam profiles in the high energy sections. These scanners provide a slow scan mode which is currently used to measure beam emittance and beam halo distributions. When operating with long bunch trains (>100 bunches) also fast scans are planned to measure beam sizes in an almost nondestructive manner. This paper describes the current installations and the latest developments of the system at European-XFEL. Furthermore, the commissioning status of the system and first results of beam halo studies will be shown.
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WEPAF048	High Resolution and Low Charge Button and Strip-Line Beam Position Monitor Electronics Upgrade at Flash	electron, electronics, laser, operation	1923
	B. Lorbeer, N. Baboi, H.T. Duhme, Re. Neumann DESY, Hamburg, Germany
	Historically the FLASH (Free Electron Laser in Hamburg) facility at DESY (Deutsches Elektronen-Synchrotron) in Germany has foreseen operation in a charge range from 1nC-3nC for which a VME based BPM(Beam Position Monitor) system has been in operation since 2005. For a couple of years the standard machine operation has been settled at a few hundreds of pC with the tendency for smaller charges down to 100pC and smaller. The availability and resolution performance of the BPM system at charges below 300pC in many locations along the machine was unsatisfactory. In the last couple of years a new BPM electronic system based on the utca standard has been developed to overcome these limitations. A substantially improved version of the analog frontend and digital electronics has been developed in 2016 and tested successfully. During shutdown works at FLASH in summer 2017 all old button and strip-line BPM electronics has been replaced with the new type of electronics. This paper summarizes the features and performance of the new BPM system, compares the beam jitter free resolution of old and new BPM system and highlights its high single shot resolution of better than 10um at a charge of 15pC.
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WEPAF049	Energy Beam Position Monitor Button Array Electronics for the European XFEL	electron, vacuum, electronics, pick-up	1927
	B. Lorbeer, B. Beutner, H.T. Duhme, L. Fröhlich, D. Lipka, D. Nölle DESY, Hamburg, Germany
	The European XFEL(X-Ray Free Electron Laser) at DESY(Deutsches Elektronen-Synchrotron) in Hamburg/Schenefeld started commissioning in early 2017. Before the pulsed electron beam is accelerated to its final energy of 14 GeV, the energy of the bunch can be compressed in three bunch compression chicanes at 130 MeV, 700 MeV and 2400 MeV. The vacuum chamber in these sections is tapered from 40 mm round beam pipe to a 40 cm rectangular shaped vacuum section. A custom made button array type of BPM(Beam position Monitor) is installed in this section with 26 button electrode feed-throughs. The analog and digital readout electronics for this monitor and the first experience with the calibration and operational aspects of this system are presented in this poster.
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WEPAF051	LLRF Operation and Performance at the European XFEL	LLRF, electron, operation, MMI	1934
	M. Omet, V. Ayvazyan, J. Branlard, L. Butkowski, M. Hierholzer, M. Killenberg, D. Kostin, L. Lilje, S. Pfeiffer, H. Schlarb, Ch. Schmidt, V. Vogel, N. Walker DESY, Hamburg, Germany
	The European X-ray Free-Electron Laser (XFEL) at Deutsches Elektronen-Synchrotron (DESY), Hamburg, Germany is a user facility providing ultrashort hard and soft X-ray flashes with a high brilliance. All LLRF stations of the injector, covering the normal conducting RF gun, A1 (8 1.3 GHz superconducting cavities (SCs)) and AH1 (8 3.9 GHz SCs), were successfully commissioned by the end of 2015. The commissioning of LLRF stations A2 to A23 (32 1.3 GHz SCs each) in the XFEL accelerator tunnel (XTL) was concluded in June 2017. SASE light was produced in SASE undulator section SA1 and delivered to the first users in September 2017, marking the beginning of regular user operation. The current state of the LLRF systems, the experience gained during operation and the performance achieved in terms of stability and energy reach are presented.
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WEPAF052	High QL and High Gradient CW Operation of Tesla SCRF 9-Cell Cavity	cavity, feedback, operation, controls	1937
	K.P. Przygoda, V. Ayvazyan, L. Butkowski, M. Hierholzer, R. Rybaniec, H. Schlarb, Ch. Schmidt, J.K. Sekutowicz DESY, Hamburg, Germany
	In the paper we would like to present Tesla SCRF 9-Cell cavity operated at CW regime with extremely high QL at gradients above 23 MV/m. The design hardware and firmware components as well as developed high level software procedures allows automatic procedure of cavity trip from low to high gradient operation. The microphonics as well as a pendoromotive effects are sensed, identify and applied for cavity detuning correction. The RF and piezo feedbacks performance are demonstrated and preliminary results are briefly discussed.
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WEPAF053	Status and Commissioning of the European XFEL Beam Loss Monitor System	electron, high-voltage, controls, hardware	1940
	T. Wamsat, T. Lensch, P.A. Smirnov DESY, Hamburg, Germany
	The European XFEL MTCA based Beam Loss Monitor System (BLM) is composed of about 450 monitors, which are part of the Machine Protection System (MPS). The BLMs detect losses of the electron beam, in order to protect accelerator components from damage and excessive activation, in particular the undulators, since they are made of permanent magnets. Also each cold accelerating module is equipped with a BLM to measure the sudden onset of field emission (dark current) in cavities. In addition some BLMs are used as detectors for wire- scanners. Experience from the already running BLM system in FLASH2 which is based on the same technology, led to a fast implementation of the system in the XFEL. Further firmware and server developments related to alarm generation and handling are ongoing. The BLM systems structure, the current status and the different possibilities to trigger alarms which stop the electron beam will be presented.
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WEPAL012	Measurements with the ELI-NP Cavity Beam Position Monitor Read-out Electronics at FLASH	electron, cavity, instrumentation, electronics	2169
	G. Franzini, D. Pellegrini, M. Serio, A. Stella, A. Variola INFN/LNF, Frascati (Roma), Italy B.B. Baricevic, M. Cargnelutti I-Tech, Solkan, Slovenia D. Lipka DESY, Hamburg, Germany M. Marongiu INFN-Roma, Roma, Italy A. Mostacci Sapienza University of Rome, Rome, Italy
	The Extreme Light Infrastructure - Nuclear Physics Gamma Beam Source (ELI-NP GBS) will be installed and commissioned starting within the next year in Magurele, Romania. It will generate gamma beam through Compton back-scattering of a recirculated laser and a multi-bunch electron beam, produced by a 720 MeV LINAC. In order to obtain bunch by bunch position measurements, four cavity beam position monitors (cBPM) near the two interaction points are foreseen. Extensive tests on the cBPM read-out electronics, recently developed by Instrumentation Technologies and acquired for ELI-NP GBS, were performed in laboratory at INFN-LNF and at FLASH in DESY, during the user operation. In the latter case, three cBPMs installed along the LINAC, with similar features as the ones of ELI-NP GBS, were used as measuring devices and signal sources for the read-out electronics under test. We present here the measurements collected and the related analysis, with a particular focus on the beam position measurement resolution.
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WEPAL026	High Repetition Rate, Single-Shot Electro-Optical Monitoring of Longitudinal Electron Bunch Dynamics Using the Linear Array Detector KALYPSO	electron, storage-ring, laser, radiation	2216
	G. Niehues, E. Blomley, M. Brosi, E. Bründermann, M. Caselle, S. Funkner, A.-S. Müller, M.J. Nasse, L. Rota, M. Schuh, P. Schönfeldt, M. Weber KIT, Eggenstein-Leopoldshafen, Germany N. Hiller PSI, Villigen PSI, Switzerland
	Funding: This work is funded by the BMBF contract numbers: 05K13VKA and 05K16VKA. High repetition rate diagnostics are required when detecting single-shot electro-optical (EO) bunch profiles. The KIT storage ring KARA (KArlsruhe Research Accelerator) is the first storage ring in the world that has a near-field EO bunch-profile monitor in operation. By imprinting longitudinal electron bunch profiles onto chirped laser pulses, single-shot detection is feasible. However, limitations of available detection systems are challenging: The constraints are either given by the repetition rate or the duration of the consecutive acquisitions. Two strategies can overcome these limitations: Based on the photonic time-stretch method, the ps laser pulses can be stretched to the ns range using km long fibers. The readout with a high-bandwidth oscilloscope then enables a single-shot detection at high repetition rates. The other strategy is the development of dedicated ultra-fast photodetector arrays allowing direct detection of the ps pulses at MHz repetition rates. We developed KALYPSO, a linear detector array with a DAQ allowing to record high data-rates over long time scales. Here, we present recent results of studies of the longitudinal electron bunch dynamics using KALYPSO.
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WEPAL045	An Electrostatic Fixed-Slit Emittance Measurement System	emittance, cathode, electron, focusing	2274
	J.W. Lewellen, H.L. Andrews, R.L. Fleming, K.E. Nichols, E.I. Simakov LANL, Los Alamos, New Mexico, USA
	Funding: Los Alamos National Laboratory LDRD Program The emittance of a field emission cathode can be difficult to measure close to the emitter, due to the high average current density of the beam and the potential for desorbed material from an imaging screen to contaminate the cathode. We present the design for a dual fixed-slit emittance measurement system for a field emitter cathode, implemented using electrostatic deflecting plates. Results from fabrication and initial testing will be presented.
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WEPAL070	HLS System to Measure the Location Changes in Real Time of PAL-XFEL Devices	alignment, linac, real-time, survey	2345
	H. J. Choi, J.H. Han, H.-S. Kang, S.H. Kim, H.-G. Lee, S.B. Lee PAL, Pohang, Kyungbuk, Republic of Korea
	All components of PAL-XFEL (Pohang Accelerator Laboratory's X-ray free-electron laser) were completely installed in December 2015, and Hard X-ray 0.1nm lasing achieved through its beam commissioning test and machine study on March 16, 2017. The beam line users has been performing various tests including pump-probe X-ray scattering, time-resolved x-ray liquidography, etc in the hard x-ray beam line since March 22. The energy and flux of x-ray photon beam generated from XFEL and synchronization timing should be stable to ensure successful time-resolved tests. Several parts that comprise the large scientific equipment should be installed and operated at precise three-dimensional location coordinates X, Y, and Z through survey and alignment to ensure their optimal performance. As time goes by, however, the ground goes through uplift and subsidence, which consequently changes the coordinates of installed components and leads to alignment errors ΔX, ΔY, and ΔZ. As a result, the system parameters change, and the performance of the large scientific equipment deteriorates accordingly. Measuring the change in locations of systems comprising the large scientific equipment in real time would make it possible to predict alignment errors, locate any region with greater changes, realign components in the region fast, and shorten the time of survey and alignment. For this purpose, a HLS's (hydrostatic leveling sensor) with 0.2um of resolution are installed and operated in a waterpipe of total length 1km in the PAL-XFEL building. This paper is designed to introduce the operating principle of the HLS, the installation and operation of the HLS system, and how to utilize the HLS system in order to ensure beam stabilization.
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WEPMF021	Magnet Design Considerations for an Ultralow Emittance Canadian Light Source	quadrupole, lattice, emittance, storage-ring	2413
	L.O. Dallin, D. Bertwistle CLS, Saskatoon, Saskatchewan, Canada
	The strong focusing requirements for ultralow emittance light sources result in high field magnets that are very close together. High fields are readily achieved by using small magnet gaps. This is possible due to the small beam sizes involved. Reduction in the physical aperture and the reduction in the good field region requirements results in magnets with compact transverse dimensions. The very strong focusing of the magnets results in very small drift spaces between the various magnetic elements. To keep these drift spaces clear magnets with recessed coils have been studied. In such magnets the coils do not stick out beyond the end of the magnet yoke in the longitudinal direction. By placing the coils on the outer yoke loss of efficiency can be avoided while maintaining good control of the higher order field harmonics. This is very well suited for quadrupole magnets where only two coils are required. Possible designs for gradient dipoles and sexutpoles are also considered.
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WEPMF053	XFEL Modulators with Pulse Cables	operation, klystron, linac, radiation	2487
	H.-J. Eckoldt, S. Choroba, T. Grevsmühl, A. Hauberg, J. Havlicek, N. Heidbrook, K. Machau, N. Ngada DESY, Hamburg, Germany M. Frei, S.G. Keens, T.H. Strittmatter Ampegon AG, Turgi, Switzerland H. Leich DESY Zeuthen, Zeuthen, Germany
	The modulators of the European XFEL produce high voltage, at the 10kV level, having a power of up to 16.8 MW for 1.54 ms. The operation frequency of the super-conducting inac is 10 Hz. The series production of the 29 modulators started in 2012. The first modulator began operation in 2014 and the start of linac was beginning 2017. The R&D phase for the modulators started directly with the development of superconducting cavities. Besides the pulse generation, the modulator had to suppress the 10 Hz repetition rate in order not to disturb the grid. Another unique demand was the development of pulse cables. Since the power RF had to be generated in the tunnel, the klystrons were installed near the cavities. However, the modulators had to be installed outside of the tunnel for space, maintenance reasons and radiation concerns. This transmission of high power pulses via long cables is unique in the world and the suppression of EMI effects was mandatory. During the first year operation no EMI disturbances of other systems were detected and the modulator system works as expected.
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WEPMF056	Cs2Te Photocathode Lifetime at Flash and European XFEL	cathode, laser, gun, operation	2496
	S. Lederer, S. Schreiber DESY, Hamburg, Germany
	The photo-injectors of FLASH and the European XFEL at DESY (Hamburg, Germany) use Cs2Te photocathodes. In this contribution we give an update on the lifetime and quantum efficiency of the cathodes operated in both facilities. Cathode #680.1 was operated at the European XFEL from the injector commissioning to the first user run for over 700 days. At FLASH cathode #73.3 has been operated with a record of more than 1000 days.
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WEPMF058	Anomaly Detection for Cavity Signals - Results from the European XFEL	cavity, flattop, beam-loading, simulation	2502
	A.S. Nawaz, S. Pfeiffer DESY, Hamburg, Germany G. Lichtenberg HAW, Hamburg, Germany P. Rostalski Institute for Electrical Engineering in Medicine, Lübeck, Germany
	The data throughput of the European XFEL DAQ is about 1.5 Gb/s. Data depicting the cavity signal behavior is currently only saved manually. This either happens, when cavity tests are being performed, or an operator detects a fault in the cavity system, that has to be further investigated. Those instances of interest are neither systematically nor automatically stored. It can therefore be assumed that unwanted or degraded cavity behavior is detected late or not at all. It is proposed to change the focus from detecting known faults (such as quenches) to additionally detect anomalies in the cavity system behavior. In order to detect anomalies in the cavity signals, an algorithm is proposed using a cavity model. It aims on finding those data sets, which diverge from the nominal cavity behavior, saving those instances for later analysis. The nominal behavior is defined by the cavity electromagnetic resonance model with beam loading as well as the model for the mechanical oscillations due to the Lorentz Forces. By using such an approach, the detection of anomalies, as well as faults could be automated. This contribution aims to summarize the influence of beam loading on the detection and gives examples for anomalies that were found in several cavities.
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WEPMF067	A High Gradient Solution for Increasing the Energy of the FERMI Linac	linac, electron, wakefield, laser	2525
	C. Serpico, I. Cudin, S. Di Mitri, N. Shafqat, M. Svandrlik Elettra-Sincrotrone Trieste S.C.p.A., Basovizza, Italy M. Bopp, R. Zennaro PSI, Villigen PSI, Switzerland
	FERMI is the seeded Free Electron Laser (FEL) user facility at Elettra laboratory in Trieste, operating in the VUV to soft X-rays spectral range. In order to extend the FEL spectral range to shorter wavelengths, a feasibility study for increasing the Linac energy from 1.5 GeV to 1.8 GeV is actually going on. The design of new S-band accelerating structures, intended to replace the present Backward Travelling Wave sections, is presented. Such design is tailored for high gradient operation, low breakdown rates and low wakefield contribution. In this paper, we will also present the first, short prototype that has been built in collaboration with Paul Scherrer Institute (PSI).
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WEPMK008	In-Depth Analysis of the Vertical Test Results of the Third-Harmonic Cavities for the E-XFEL Injector	cavity, experiment, feedback, SRF	2644
	M. Bertucci, A. Bignami, A. Bosotti, J.F. Chen, C.G. Maiano, P. Michelato, L. Monaco, R. Paparella, P. Pierini, D. Sertore INFN/LASA, Segrate (MI), Italy C.G. Maiano, P. Pierini ESS, Lund, Sweden C. Pagani Università degli Studi di Milano & INFN, Segrate, Italy
	The results of the vertical tests performed at LASA on the 3.9 GHz third-harmonic cavities for the E-XFEL injector are here discussed. Analysis of experimental data allows to confirm that such high frequency cavity, prepared with standard BCP treatment and 800°C annealing treatment, suffers an intrinsic performance limitation at around 22 MV/m (@ 2 K) due to a global thermal dissipation mechanism. A quantitative interpretation of the high field Q slope is also presented according to the latest theoretical models of field-dependent surface resistance.
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WEPMK010	LCLS-II Cryomodules Production at Fermilab	cryomodule, cavity, vacuum, controls	2652
	T.T. Arkan, J.N. Blowers, C.M. Ginsburg, C.J. Grimm, J.A. Kaluzny, A. Lunin, Y.O. Orlov, K.S. Premo, R.P. Stanek, G. Wu Fermilab, Batavia, Illinois, USA
	Funding: DOE LCLS-II is a planned upgrade project for the linear coherent light source (LCLS) at SLAC. The LCLS-II linac will consist of thirty-five 1.3 GHz and two 3.9 GHz superconducting RF continuous wave (CW) cryomodules that Fermilab and Jefferson Lab are currently producing in collaboration with SLAC. The LCLS-II 1.3 GHz cryomodule design is based on the European XFEL pulsed-mode cryomodule design with modifications needed for CW operation. Two prototype cryomodules had been assembled and tested. After prototype cryomodule tests, both laboratories have increased cryomodule production rate to meet the challenging LCLS-II project installation schedule requirements of approximately one cryomodule per month per laboratory. Fermilab is at half point for the production, meaning that 6 cryomodules are fully assembled and tested. This paper presents Fermilab Cryomodule Assembly Facility (CAF) infrastructure for the LCLS-II cryomodules assembly, production experience at the half point emphasizing the challenges and mitigations.
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WEPML008	Tuner Testing of a Dressed 3.9 GHz Cavity for LCLS-II at Fermilab	cavity, SRF, operation, background	2690
	J.P. Holzbauer, S. Aderhold, T.N. Khabiboulline, Y.M. Pischalnikov, W. Schappert, J.C. Yun Fermilab, Batavia, Illinois, USA C. Contreras-Martinez FRIB, East Lansing, USA
	Funding: This manuscript has been authored by Fermi Research Alliance, LLC under Contract No. DE-AC02-07CH11359 with the U.S. Department of Energy, Office of Science, Office of High Energy Physics. Fermilab is responsible for the design of the 3.9 GHz cryomodule for LCLS-II. Integrated acceptance testing of a dressed 3.9 GHz cavity for the LCLS-II project has been done at the Fermilab Horizontal Test Stand. This test included a slim blade tuner (based on INFN & XFEL designs) with integrated piezoelectric fast/fine tuner. This paper will present results of the mechanical setup, cold testing, and cold function of this tuner including fast and slow tuner range, sensitivity, and hysteresis.
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WEPML023	Design and Test Results of the 3.9 GHz Cavity for LCLS-II	cavity, radiation, cryomodule, operation	2730
	N. Solyak, S. Aderhold, S.K. Chandrasekaran, C.J. Grimm, T.N. Khabiboulline, A. Lunin, O.V. Prokofiev, G. Wu Fermilab, Batavia, Illinois, USA
	The LCLS-II project uses sixteen 3.9 GHz superconduct-ing cavities to linearize energy distribution before the bunch compressor. To meet LCLS-II requirements origi-nal FNAL design used in FLASH and XFEL was signifi-cantly modified to improve performance and provide reliable operation up to 16 MV/m in cw regime [1-3]. Four prototype cavities were built and tested at vertical cryo-stat. After dressing, one cavity was assembled and tested at horizontal cryostat as part of design verification pro-gram. All auxiliaries (magnetic shielding, power and HOM couplers, tuner) were also re-designed and tested with this cavity. In this paper we will discuss cavity and coupler design and test results.
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THXGBD2	Overview of Undulator Concepts for Attosecond Single-Cycle Light	electron, undulator, laser, bunching	2878
	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 THXGBD2 [1.758 MB]
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THYGBE1	Applying Artificial Intelligence to Accelerators	controls, feedback, electron, network	2925
	A. Scheinker, R.W. Garnett, D. Rees LANL, Los Alamos, New Mexico, USA D.K. Bohler SLAC, Menlo Park, California, USA A.L. Edelen, S.V. Milton CSU, Fort Collins, Colorado, USA
	Particle accelerators are being designed and operated over a wide range of complex beam phase space distributions. For example, the Linac Coherent Light Source (LCLS) upgrade, LCLS-II, is considering complex schemes such as two-color operation [1], while the plasma wake field acceleration facility for advanced accelerator experimental tests (FACET) upgrade, FACET-II, is planning on providing custom tailored current profiles [2]. Because of uncertainty due to limited diagnostics and time varying performance, such as thermal drifts, as well as collective effects and the complex coupling of large numbers of components, it is impossible to use simple look up tables for parameter settings in order to quickly switch between widely varying operating ranges. Several forms of artificial intelligence are currently being investigated in order to enable accelerators to quickly and automatically re-adjust component settings without human intervention. In this work we discuss recent progress in applying neural networks and adaptive feedback algorithms to enable automatic accelerator tuning and optimization. [1] A. A. Lutman et al., Nat. Photonics 10.11, 745 (2016). [2] V. Yakimenko et al., IPAC2016, Busan, Korea, 2016.
	Slides THYGBE1 [14.256 MB]
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THPAF006	Simulations of Cooling Rate and Diffusion for Coherent Electron Cooling Experiment	electron, simulation, kicker, bunching	2957
	J. Ma, V. Litvinenko, G. Wang BNL, Upton, Long Island, New York, USA V. Litvinenko Stony Brook University, Stony Brook, USA
	Start-to-end numerical simulations have been performed using the code SPACE and GENESIS for the single pass of gold ions through the coherent electron cooling (CeC) device installed in the Relativistic Heavy Ion Collider (RHIC) at Brookhaven National Laboratory (BNL). Cooling rate of CeC experiment has been predicted using off-reference energy ions in a finite Gaussian electron beam through a realistic beam-line, in which settings of quadrupoles and free-electron laser (FEL) device are relevant to BNL RHIC.
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THPAF033	Degradation of Electron Beam Quality for a Compact Laser-Based FEL	electron, emittance, laser, space-charge	3029
	A.Y. Molodozhentsev, L. Pribyl Czech Republic Academy of Sciences, Institute of Physics, Prague, Czech Republic K.O. Kruchinin ELI-BEAMS, Prague, Czech Republic
	Laser wake field acceleration (LWFA) mechanism allows to produce extremely short electron bunches of a few fs length with the energy up to a few GeV in extremely compact geometries providing unique electron beam parameters, in particular, transverse beam emittance (order of 1pi mm mrad), extremely short bunch length and high beam charge (up to 100pC) . This novel acceleration method therefore opens a new way to develop compact 'laser-based' FELs. In the frame of this report we analyze effects, which lead to degradation of an electron beam quality. The chromatic and collective effects are analyzed for a compact dedicated electron beam line to transport the electron beam to an undulator. In addition, the SASE FEL performance has been discussed taking into consideration the degradation of the electron beam quality.
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THPAK010	Optimization on the Optical Resonator of CTFEL	GUI, radiation, coupling, electron	3228
	X.J. Shu, Y.H. Dou Institute of Applied Physics and Computational Mathematics, People's Republic of China M. Li, Z. Xu, Y. Xu, X. Yang CAEP/IAE, Mianyang, Sichuan, People's Republic of China
	Funding: Program for the National Science Foundation of China (Grant No. 11105019) and the National Science Device Exploitation Foundation of China (Grant No. 2011YQ130018). A high power THz free electron laser (FEL) facility is under construction at China Academy of Engineering Physics (CTFEL) since October, 2011. The radiation frequency of the FEL facility will be tuned in range of 1~3 THz and the average output power is about 10 W. The system mainly consists of a GaAs photoemission DC gun, superconductor accelerator, the hybrid wiggler, optical cavity. The first lasing is obtained on Aug. 29, 2017. The optical resonator of CTFEL is optimized to ensure wavelength tunable in a wide range and high power operation. The FEL power strongly depends on the performance of the optical resonator including output efficiency, gain and round-trip loss. The optical resonator consists of metal-coated reflect mirror, the center-hole output mirror, waveguide. The influence of waveguide and Rayleigh length on the quality of optical cavity is evaluated by the 3D-OSIFEL code. The waveguide size, mirror curvature radius, output hole radius is optimized to different frequencies between 1 THz to 3 THz.
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THPAK064	Theoretical Modeling of Electromagnetic Field from Electron Bunches in Periodic Wire Medium	radiation, simulation, electron, lattice	3376
	S.S. Chuchurka, A.I. Benediktovitch BSU, Minsk, Belarus, Belarus S.N. Galyamin, V.V. Vorobev Saint Petersburg State University, Saint Petersburg, Russia A. Halavanau Northern Illinois University, DeKalb, Illinois, USA
	Funding: Work supported by the Grant from Russian Foundation for Basic Research (No. 17-52-04107). The interaction of relativistic electrons with periodic structures results in radiation by a number of mechanisms. In case of crystals one obtains parametric X-ray radiation, its frequency is determined by distance between crystallographic planes and direction of electron beam. If instead of crystal one considers a periodic structure of metallic wires with period of the order of mm, one can expect emission of THz radiation. In the present contribution we consider theoretical approaches for modeling of the distribution of electromagnetic field from electron bunches in lattice formed by metallic wires. The analytical description is possible for the case of wires with small radius, the range of validity is checked by numerical simulations. The intensity of radiation will be significantly increased if the electrons in the bunch could radiate coherently. Two possibilities will be discussed: the prebunching of the beam and the self-modulation of the beam due to interaction with radiated field.
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THPAK074	Beam Manipulation Using Self-Induced Fields in the SwissFEL Injector	wakefield, electron, experiment, laser	3401
	S. Bettoni, P. Craievich, R. Ganter, P. Heimgartner, H. Jöhri, F. Marcellini, S. Reiche PSI, Villigen PSI, Switzerland
	Several possibilities of manipulating the electron beam using sources of wakefield are being explored. Wakefield have been successfully used to remove or enhance the energy chirp residual from the magnetic compression to control the free electron laser bandwidth (dechirper), to linearize the compressed beam (linearizer), to generate more bunches to produce two color mode, and to perform experiments of wakefield acceleration. At the SwissFEL injector we plan to install 2 m long system to accommodate sources of wakefield with different periodicities, each of them associated with one of the discussed beam manipulation. In this paper we summarize the design and the characterization of the system and the planned activities.
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THPAK136	Wide-Ranging Genetic Research of Matching Line Design for Plasma Accelerated Beams with GIOTTO	plasma, emittance, electron, target	3561
	M. Rossetti Conti Universita' degli Studi di Milano & INFN, Milano, Italy A. Bacci, A.R. Rossi Istituto Nazionale di Fisica Nucleare, Milano, Italy A. Giribono, C. Vaccarezza INFN/LNF, Frascati (Roma), Italy
	GIOTTO is a code based on a Genetic Algorithm, being used in the field of particles accelerators for some years-. Its main use concerns beam-dynamics optimizations for low energy linacs, or injectors, where the beam space-charge plays an important role on its dynamics. Typical optimizations regard the Velocity Bunching technique or, more generally, the emittance and energy spread minimization. Recent improvements in GIOTTO, here discussed, have added the important capability to solve problems with a wide research domain, making GIOTTO able to design a beam Transfer Line (TL) from scratch*. The code, taking as input the TL length and the optics elements, can define the correct lattice of the line that transports and matches the beam from the linac to the undulators of an FEL, finding the right gradients, positions and dimensions for the optics elements by exploring the parameters values in selected ranges. Further, the introduction of Twiss parameters into the fitness function makes GIOTTO a powerful tool in the design of highly different beam lines. Lastly, a new routine for the statistical analysis of parameters jitters effects on the beam is under development. Bacci et al, NIM-B, 263, 488 (2007) Bacci et al, presented at PAC'07, THPAN031 Bacci et al, presented at IPAC'16, WEPOY039 ***Rossetti Conti et al, NIM-A (2018, in press)
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THPAK138	Development of Efficient Tree-Based Computation Methods for the Simulation of Beam Dynamics in Sparsely Populated Phase Spaces	simulation, electron, bunching, HOM	3569
	Ph. Amstutz University of Hamburg, Institut für Experimentalphysik, Hamburg, Germany M. Vogt DESY, Hamburg, Germany
	Collective instabilities pose a major threat to the quality of the high brightness electron beams needed for the operation of a free electron laser. Multi-stage bunch compression schemes have been identified as a possible source of such an instability. The dispersive sections in these compressors translate energy inhomogeneities within the bunch into longitudinal charge density inhomogeneities. In conjunction with a collective force driving locally density-dependent energy modulations this leads to intricate longitudinal beam dynamics. As a consequence of the thin shape those bunches form in the longitudinal phase space, efficient simulation of such systems is not straight forward. At high resolutions, the numerical representation of the phase space density on a uniform grid is too wasteful, due to the large unpopulated phase space regions. In this contribution we present advances made in the development of a simulation code that addresses the problem of sparsely populated phase spaces by means of quadtree domain decomposition. A focus lies on the explanation of the underlying tree data structure.
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THPAL068	Status of the Polarix-TDS Project	electron, undulator, status, klystron	3808
	P. Craievich, M. Bopp, H.-H. Braun, R. Ganter, T. Kleeb, M. Pedrozzi, E. Prat, S. Reiche, R. Zennaro PSI, Villigen PSI, Switzerland R.W. Aßmann, F. Christie, R.T.P. D'Arcy, U. Dorda, M. Foese, P. González Caminal, M. Hoffmann, M. Hüning, R. Jonas, O. Krebs, S. Lederer, V. Libov, B. Marchetti, D. Marx, J. Osterhoff, F. Poblotzki, M. Reukauff, H. Schlarb, S. Schreiber, G. Tews, M. Vogt, A. Wagner DESY, Hamburg, Germany N. Catalán Lasheras, A. Grudiev, G. McMonagle, W. Wuensch CERN, Geneva, Switzerland
	A collaboration between DESY, PSI and CERN has been established to develop and build an advanced modular X-band transverse deflection structure (TDS) system with the new feature of providing variable polarization of the deflecting force. This innovative CERN design requires very high manufacturing precision to guarantee highest azimuthal symmetry of the structure to avoid the deterioration of the polarization of the streaking field. Therefore, the high-precision tuning-free production process developed at PSI for the C-band and X-band accelerating structures will be used for the manufacturing. We summarize in this paper the status of the production of the prototype and the waveguide networks foreseen in the different facilities.
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THPAL084	An X-Band Lineariser for the CLARA FEL	cavity, simulation, wakefield, klystron	3848
	L.S. Cowie, A.D. Brynes, J.K. Jones, A.E. Wheelhouse, P.H. Williams STFC/DL/ASTeC, Daresbury, Warrington, Cheshire, United Kingdom R. Apsimon, G. Burt, W.L. Millar Cockcroft Institute, Lancaster University, Lancaster, United Kingdom Ö. Mete UMAN, Manchester, United Kingdom A.J. Moss STFC/DL, Daresbury, Warrington, Cheshire, United Kingdom
	The CLARA FEL at Daresbury Laboratory will employ four S-band linacs to accelerate electron bunches to 250 MeV/c. In order to compress the bunch sufficiently to achieve peak currents suitable for FEL lasing, one must compensate for curvature imprinted on the longitudinal phase space of the bunch. For CLARA a harmonic RF linearization system has been designed to achieve this requirement. The linearization will be achieved by an X-band travelling wave cavity of the PSI/CERN design, which incorporates wake-field monitoring of the bunch position. A five-axis mover will align the cavity to the beam axis. Pulse compression of a 6 MW klystron pulse will provide the required power to achieve a 30 MV/m operational gradient.
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THPAL101	Longitudinal Effects of Trapped Homs in Shanghai Coherent Light Facility	cavity, HOM, linac, impedance	3872
	J.J. Guo, Q. Gu, H.T. Hou, J.H. Tan, M. Zhang SINAP, Shanghai, People's Republic of China
	Funding: Shanghai Institute of Applied Physics, Chinese Academy of Sciences Shanghai Coherent Light Facility (SCLF), a superconducting accelerated structure-baesd FEL device, is now under development at Shanghai Institute of Applied Physics, Chinese Academy of Sciences. We investigate effects of cryogenic losses caused by trapped longitudinal high order modes (HOM). Results of calculations are presented for losses caused by HOMs excitation in the acceleration RF system of the continues-wave (CW) linac of SCLF.
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THPAL102	Design a High Power Pulse Transformer for C-band Klystron Modulator	flattop, klystron, high-voltage, plasma	3875
	Y.F. Liu, Z.H. Chen, M. Gu, Y. Wu, Q. Yuan, X.X. Zhou SINAP, Shanghai, People's Republic of China
	Shanghai soft X-ray Free Electron Lasers (SXFEL) first uses C band accelerator structure to accelerate electrons at SINAP. SXFEL is an X-ray free electron laser facility, which requests very stable amplitude stability and very tight tolerances of phase jitter. 50MW C-band klystron and 110MW modulator is used to provide power supply for accelerator structure. Typical specifications of the modulator are peak beam voltage 350KV, peak beam current 320A, 10Hz repetition rate, 3us flat-top pulse width. In order to meet these demands, we developed a reliable and stable high power pulse transformer. In this paper, the analysis and design of high power pulse transformer for C band klystron modulator are presented. The methods of shortening rise time, diminishing droop and diminishing flat top oscillation are highlighted. Detailed design, simulation and relevant experimental results are given. The relevant experiments show that this pulse transformer can meet the requirement of 50MW C band klystron.
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THPAL118	Critical Fields of SRF Materials	niobium, cavity, interface, superconductivity	3921
	T. Junginger TRIUMF, Vancouver, Canada T. Prokscha, Z. Salman, A. Suter PSI, Villigen PSI, Switzerland A-M. Valente-Feliciano JLab, Newport News, Virginia, USA
	Nb3Sn and NbTiN are two potential alternative materials to niobium for superconducting RF cavities. In this study direct measurements of the magnetic penetration depth using the low energy muon spin rotation technique are presented, from which the lower critical field and the superheating field are derived. Comparison with RF data confirms that the lower critical field is not a fundamental limitation and predict a potential performance clearly exceeding current state of the art of niobium technology if the superheating field can be achieved. As a potential pathway to avoid premature vortex penetration and reaching the superheating field it is suggested to use a bilayer structure with the outer layer having a larger magnetic penetration depth.
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THPAL128	Autonomous Topography Detection and Traversal for an Inspection Robot Within the Beamline of Particle Accelerators	vacuum, experiment, kicker, heavy-ion	3943
	N. Schweizer Technische Universität Darmstadt (TU Darmstadt, RMR), Darmstadt, Germany I. Pongrac GSI, Darmstadt, Germany
	Particle accelerators feature ultra-high vacuum pipe systems with unique topography, i.e. with a multitude of different vacuum chambers of varying dimensions and varying pipe apertures. In order to be able to examine the interior of the entire vacuum system, even those parts which are not accessible without disassembling large parts of the accelerator, a semi-autonomous robot is being developed which shall traverse and visually inspect the vacuum system of particle accelerators. We present a generic concept based on distance sensors for the inspection robot to detect steps between vacuum chambers and gaps in the beamline. Movement strategies to autonomously overcome these basic obstacles are introduced. For evaluation we use simulations of ideal environments with flat surfaces as well as realistic beam pipe environments of the SIS100 particle accelerator. Additionally, a prototype of our robot concept confirms the implementation of all maneuvers. Results show that obstacles of previously unknown dimensions can be detected and reliably traversed.
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THPAL142	Surface Characterization of NbTiN Films for Accelerator Applications	site, SRF, detector, lattice	3975
	D.R. Beverstock, M.J. Kelley, C.E. Reece, J.K. Spradlin, A-M. Valente-Feliciano JLab, Newport News, Virginia, USA
	Funding: Work supported by Jefferson Science Associates, LLC under U.S. DOE Contract No. DE-AC05-06OR23177. The development of next-generation SRF cavities requires the deployment of innovative material solutions with RF performance beyond bulk Nb. Theoretical interest has stimulated efforts to grow and characterize thin multi-layer superconductor/insulator/superconductor (SIS) structures for their potential capability of supporting otherwise inaccessible surface magnetic fields in SRF cavities . The ternary B1-compound NbTiN is among the candidate superconducting materials for SIS structures. Single crystal NbTiN films with thicknesses below 15 nm are also of interest for the development of high resolution, high sensitivity (SNSPD) detectors for particle physics application. Using DC reactive magnetron sputtering, NbTiN can be deposited with nominal superconducting parameters. This contribution presents the on-going material surface and superconducting properties characterization in order to optimize the NbTiN films for each application. A Gurevich, "Maximum screening fields of superconducting multilayer structures", AIP ADVANCES 5, 017112 (2015)
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THPAL153	High Power Test of the S-Band Spherical Pulse Compressor at Tsinghua University	cavity, coupling, polarization, klystron	4008
	P. Wang, D.Z. Cao, H.B. Chen, C. Cheng, J. Shi, Z.H. Wang, H. Zha TUB, Beijing, People's Republic of China
	We designed, fabricated and high power tested an S-band spherical pulse compressor for the high-power test facility at Tsinghua University. The pulse compressor comprises a spherical resonant cavity with an unloaded quality factor of 100, 000 and an RF polarizer with two rectangular ports and a circular port. To achieve high efficiency and large power gain, the coupling coefficient was optimized to 8 with input pulse length of 3.6 us and compression ratio of 12. After conditioning the RF system, the pulse compressor generated RF pulses with peak power of more than 400MW. And during the operation, the pulse compressor has very low breakdown rate and was extremely stable.
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THPMF012	Tapered Flying Radiofrequency Undulator	undulator, electron, simulation, ECR	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%).
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THPMF016	Design of a Terahertz Radiation Source for Pump-Probe Experiments	bunching, undulator, radiation, electron	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.
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THPMF022	Study of Possible Beam Losses After Post-Linac Collimation at European XFEL	undulator, radiation, simulation, vacuum	4092
	S. Liu, W. Decking DESY, Hamburg, Germany F. Wolff-Fabris XFEL. EU, Schenefeld, Germany
	The European XFEL has been operating with the undulator beam line SASE1 and SASE3 since April 2017 and February 2018, respectively. Despite of the fact that the post-linac collimation has collimated the beam halo to ~20 σ level, relative high radiation doses have been measured especially in the diagnostic undulator (DU) section. In order to find the sources of beam losses after post-linac collimation, BDSIM simulations have been performed. In this paper, we will first present the possible losses generated by the wire scanners upstream of the undulators during a scan. The simulation results will be compared with the measured doses along SASE1 and SASE3 undulators. Based on the simulation results, we will estimate the frequency for wire scanner opera-tions. Besides, the simulations with large extension of beam halo hitting the vacuum chamber aperture transition will also be presented. Finally, other possible radiation dose sources will be discussed. S. Liu et al., in Proc. of FEL 2017, Santa-Fe, USA, Aug. 2017, paper TUP003. ** F. Wolff-Fabris et al.,IPAC-2018 contribution.
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THPMF031	In-Vacuum APPLE II Undulator	vacuum, undulator, cryogenics, operation	4114
	J. Bahrdt, W. Frentrup, S. Grimmer, C. Kuhn, C. Rethfeldt, M. Scheer, B. Schulz HZB, Berlin, Germany
	APPLE II undulators are widely used in many synchrotron radiation facilities for the generation of arbitrarily polarized light, because they provide the highest magnet fields among all planar variably polarizing permanent magnet undulators (PMUs). So far, in-vacuum permanent magnet undulators (IVUs) have a fixed polarization, either planar or elliptical / helical. A variably polarizing in-vacuum undulator was never built due to the engineering challenges. We present the design of a new in-vacuum APPLE II, which will extend the photon energy range to tender X-rays in the 1.7 GeV storage ring BESSY II.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2018-THPMF031
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THPMF050	High-Efficient XFELO Based on Optical Resonator with Self-Modulated Q-Factor	undulator, laser, coupling, electron	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.
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THPMF058	The MariX source (Multidisciplinary Advanced Research Infrastructure with X-rays)	electron, cavity, gun, radiation	4199
	V. Petrillo, N. Piovella Universita' degli Studi di Milano, Milano, Italy A. Bacci, F. Castelli, S. Cialdi, C. Curatolo, I. Drebot, D. Giannotti, D. Giove, C. Meroni, A.R. Rossi, L. Serafini, M. Statera, V. Torri Istituto Nazionale di Fisica Nucleare, Milano, Italy A. Bosotti, F. Broggi, F. Groppi, P. Michelato, L. Monaco, R. Paparella, D. Sertore INFN/LASA, Segrate (MI), Italy R. Calandrino, A. Delvecchio HSP, Milan, Italy F. Camera, S. Coelli, G. Onida, B. Paroli, L. Perini, F. Prelz, M. Rossetti Conti, F. Tomasi Universita' degli Studi di Milano & INFN, Milano, Italy P. Cardarelli, M. Gambaccini, G. Paternò, A. Taibi INFN-Ferrara, Ferrara, Italy A. Castoldi, G. Ghiringhelli, C. Guazzoni, M. Moretti, E. Pinotti Polytechnic of Milan, Milano, Italy S. Di Mitri Elettra-Sincrotrone Trieste S.C.p.A., Basovizza, Italy A. Esposito, A. Gallo, C. Vaccarezza INFN/LNF, Frascati (Roma), Italy L. Faillace RadiaBeam, Santa Monica, California, USA G. Galzerano, E. Puppin, A. Tagliaferri Politecnico/Milano, Milano, Italy G. Mettivier, P. Russo UniNa, Napoli, Italy M. Placidi LBNL, Berkeley, California, USA G. Rossi Università degli Studi di Milano, Milano, Italy R.I. Saban CERN, Geneva, Switzerland A. Sarno INFN-Napoli, Napoli, Italy F. Stellato INFN - Roma Tor Vergata, Roma, Italy G. Turchetti Bologna University, Bologna, Italy
	MariX (Multidisciplinary advanced research infra-structure with X-rays) is a joint project of INFN and University of Milan, aiming at developing a twin X-ray Source of advanced characteristics for the future Sci-entific Campus of the University of Milan. Presently in its design study phase, it will be built in the post Expo area located in north-west Milan district. The first component of the X-source MariX is BriXS (Bright and compact X-ray Source), a Compton X-ray source based on superconducting cavities technology for the electron beam with energy recirculation and on a laser system in Fabry-Pérot cavity at a repetition rate of 100 MHz, producing 20-180 keV radiation for medical applications. The BriXS accelerator is also serving as injector of a 3.8 GeV superconductive linac, driving a X-ray FEL at 1 MHz, for providing coherent, moderate flux radiation at 0.3-10 KeV at 1 MHz. Scientific case, layout and typical parameters of MariX will be discussed.
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THPMF076	New Simulation Programs for Partially Stripped Ions - Laser Light Collisions	photon, laser, electron, factory	4249
	C. Curatolo, L. Serafini Istituto Nazionale di Fisica Nucleare, Milano, Italy M.W. Krasny LPNHE, Paris, France W. Placzek Marian Smoluchowski Institute of Physics, Jagiellonian University, Kraków, Poland
	We present for the first time two new indipendent Monte Carlo codes for simulating the collisions of Partially Stripped Ions with Laser light. Such collisions if realised at LHC could drive a high intensity gamma source and are the back-bone of the recent Gamma Factory proposal. The implementation aspects will be discussed and the simulation results will be compared.
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THPMF082	Suppression of Microbunching Instability Using a Quadrupole Inserted Chicane in Free-Electron-Laser Linacs	bunching, linac, electron, laser	4267
	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	micro-particles, bunching, radiation, electron	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	wiggler, simulation, laser, plasma	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.
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THPMK016	Simulation Study of the NSRRC High Brightness Linac System and Free Electron Laser	linac, undulator, simulation, electron	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.
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THPMK026	Mobile Free-Electron Laser for Remote Atmospheric Survey	laser, electron, survey, free-electron-laser	4351
	S. Johnson, G.A. Krafft, B. Terzić ODU, Norfolk, Virginia, USA G.A. Krafft JLab, Newport News, Virginia, USA
	Funding: This paper is authored by Jefferson Science Associates, LLC under U.S. DOE Contract No. DE-AC05- 06OR23177. E.J. was supported by the Virginia Space Grant Consortium, grant number 16-589. Reliable atmospheric surveys for carbon distributions will be essential to building an understanding of the Earth's carbon cycle and the role it plays in climate change. One of the core needs of NASA 's Active Sensing of CO2 Over Nights, Days and Seasons (ASCENDS) Mission is to advance the range and precision of current remote atmospheric survey techniques. The feasibility of using accelerator-based sources of infrared light to improve current airborne lidar systems has been explored. A literary review has been conducted to asses the needs of ASCENDS versus the current capabilities of modern atmospheric survey technology, and the parameters of a free electron laser (FEL) source were calculated for a lidar system that will meet these needs. By using the "Next Linear Collider" from the Stanford Linear Accelerator Center (SLAC), a mobile FEL-based lidar may be constructed for airborne surveillance. The calculated energy of the lidar pulse is 0.1 joule: this output is a two orders of magnitude gain over current lidar systems, so in principle, the mobile FEL will exceed the needs of ASCENDS. Further research will be required to asses other challenges to mobilizing the FEL technology.
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THPMK028	Inverse Free Electron Laser Separatrix Crossing for Energy Gain and Stability	laser, undulator, electron, free-electron-laser	4354
	N.S. Sudar, P. Musumeci UCLA, Los Angeles, USA D. Garzella CEA, Gif-sur-Yvette, France
	The laser wakefield accelerator (LWFA) has been proposed as a driver for next generation compact light sources. However, the beams produced by LWFA's typically exhibit correlated energy spread and energy jitter too large to drive the Free Electron Laser instability. We present here a novel scheme whereby using a highly non-linear strongly tapered undulator interaction directly after the LWFA we are able to trap and accelerate a large fraction of charge in the moving Inverse Free Electron Laser ponderomotive bucket. The final correlated energy spread and output energy are determined by the final bucket height and central energy of the ponderomotive bucket which are both determined by the stagnant undulator parameters, resulting in a significant decrease in the normalized energy spread (< 1%) and output energy jitter (< 1%). This interaction is treated both analytically and numerically.
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THPMK031	Elliptically Polarizing Undulator Design for PAL-XFEL	undulator, controls, operation, electron	4362
	S.J. Lee, J.H. Han, D.E. Kim PAL, Pohang, Kyungbuk, Republic of Korea
	Funding: This research was supported by Basic Science Research Program through the National Research Foundation of Korea (NRF) funded by the Ministry of Science and ICT (2017R1C1B1012852). Elliptically polarizing undulator (EPU) is under consideration as after-burner for the PAL-XFEL soft X-ray beamline to control the FEL polarization. In the soft X-ray line, seven planar undulators with a 35 mm period and 5 m length are in operation. To provide a polarization control of the FEL in the 1 to 3 nm wavelength, we compare the two types of EPUs, APPLE-II, and APPLE-X. The K value ranges for various operation modes are numerically studied for two undulator periods, 35 and 40 mm, of these EPU types.
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THPMK032	RADFET Installation at PAL-XFEL Undulator	undulator, radiation, controls, operation	4366
	J.H. Han, Y.G. Jung, D.E. Kim, S.J. Lee, G. Mun PAL, Pohang, Kyungbuk, Republic of Korea
	Two undulator beamlines, one hard X-ray and one soft X-ray, are in operation at PAL-XFEL. Radiation produced during the FEL operation may impair the magnetic property of the undulator magnets and affect the FEL performance. Accumulated radiation at the undulator sections is being measured by using optically stimulated luminescent dosimeters (OSLDs) once per few months. Over 10 Gy gamma ray was detected at some locations at both undulator beamlines. However, in the measurement using the OSLDs we do not have information on which accelerator operation modes produce such high level of radiation on the undulators. To measure accumulated radiation in real time, we installed radiation-sensing field-effect transistors (RADFETs). We report the characteristics of the RADFET sensors and the installation at the PAL-XFEL undulator beamlines.
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THPMK033	PAL-XFEL Linac RF System Status	klystron, controls, operation, electron	4369
	H.-S. Lee, Heo, J.Y. Heo, J.H. Hong, H.-S. Kang, K.H. Kim, S.H. Kim, D.H. Na, S.S. Park, Y.J. Park PAL, Pohang, Kyungbuk, Republic of Korea
	Funding: Ministry of Science and ICT The PAL-XFEL Linear Accelerator began user support in March 2017 after one year of RF conditioning in 2016. The energy jitter was 0.013% when operating the H-X linear accelerator with 46 modulators, Klystron, LLRF, SSA and vacuum system at 6.838 GeV energy during user support period. So far, we have replaced four klystrons and 10 thyratron switches. We also measured the influence of temperature changes of RF components according to repetition rates of the machine. We will report on the measurement results of this operating experience and performance.
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THPMK034	Study on Effect of Phase Shifter on FEL Intensity at PAL-XFEL	undulator, electron, radiation, simulation	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.
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THPMK042	Two and Multiple Bunches at LCLS	laser, undulator, diagnostics, photon	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.
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THPMK043	Timing Stability at LCLS	timing, cavity, laser, linac	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.
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Paper

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Other Keywords

Page

MOZGBD1

Towards Full Performance Operation of SwissFEL

experiment, photon, electron, laser

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 MOZGBD1 [11.391 MB]

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MOZGBD2

FEL Performance Achieved at European XFEL

photon, MMI, undulator, electron

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 MOZGBD2 [18.822 MB]

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MOZGBD5

A Proposal for Coherent Hard X-Ray Generation Based on Two-Stage EEHG

electron, laser, linac, radiation

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 MOZGBD5 [7.330 MB]

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MOPMF044

New Coordination Tools to Prepare Programmed Stops in the LHC and its Injectors

simulation, hardware, MMI, dipole

200

S. Chemli, M. Bernardini, T.W. Birtwistle, A. Bolognesi, B. Brito Da Palma, S.E. Bustamante, J. Coupard, K. Foraz, E. Kleszcz, N. Kotsolakos, T. Krastev, P. A. Kulig, Y. Muttoni, B. Nicquevert, L. Pater, A. Patrascoiu, S. Petit, C. Rauser, A. Wardzinska
CERN, Geneva, Switzerland

The LHC and its Injectors are submitted to an overall lifecycle of three to four years of physics delivery to Experiments with a two-year long stop, also known as Long Shutdown (LS). The years of physics delivery are ended by a programmed stop for the immediate preventive and corrective maintenance, also known as (Extended)-Year-End Technical Stop - (E)YETS. This regular cycle is to be addressed in parallel with other projects: the upgrade projects to the accelerator complex of the LHC (High-Luminosity project) and to its Injectors (LHC Injectors Upgrade), and the "standard" consolidation tasks. This paper describes the way the programmed stops coordination group prepares the activities to take place during the stop with a set of new tools and processes that ease the communication between the stakeholders of the coordination.

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MOPML047

Diversified Application of ILC

photon, neutron, scattering, electron

502

Y. Iwashita
Kyoto ICR, Uji, Kyoto, Japan
T. Hayakawa
QST, Tokai, Japan
N. Kawamura, S. Makimura, K. Mishima, D. Nomura, K. Shimomura, S. Yamamoto, T. Yamazaki
KEK, Ibaraki, Japan

ILC will be a very powerful accelerator complex. It has not only the high power energetic electron beam but also positron and photon beams. In addition to these beams, large cryogenic plants are equipped together with various utility facilities. Some suggestions on the assumption of availability of ILC are offered from various fields. These discussions will be reported.

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MOPML068

Training the Next Generation of Accelerator Experts

network, laser, electron, synchrotron

564

C.P. Welsch
The University of Liverpool, Liverpool, United Kingdom
C.P. Welsch
Cockcroft Institute, Warrington, Cheshire, United Kingdom

Funding: Work supported by the European Union under grant agreements no 215080, 289191, 289485, 675265 and 721559.
Close collaboration between academia, research centres and industry has turned out to be crucial for the advancement of accelerator science and technology. It is also ideal for providing an efficient training of the next generation of particle accelerator experts and for linking the global accelerator community. Five international research and training networks (DITANET, oPAC, LA3NET, OMA and AVA) have been initiated and coordinated by the University of Liverpool/Cockcroft Institute since 2007. These networks have provided training to almost 100 Fellows from all over the world and organised dozens of international schools, topical workshops and international conferences for the accelerator community. The research activities of the networks have led to hundreds of journal publications and conference proceedings. This contribution presents the best practice in establishing such international collaborative projects, how to establish successful links between sectors and countries, and highlights the main research results that resulted from the research programs.

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MOPML069

Enhancing Hadron Therapy through OMA

proton, simulation, medical-accelerators, hadron

568

C.P. Welsch
The University of Liverpool, Liverpool, United Kingdom
C.P. Welsch
Cockcroft Institute, Warrington, Cheshire, United Kingdom

Funding: This project has received funding from the European Union's Horizon 2020 research and innovation programme under the Marie SkłodowskaCurie grant agreement No 675265.
Continued research into the optimization of medical accelerators is urgently required to assure the best possible cancer care for patients and this is one of the central aims of the OMA project which received 4 M€ of funding from the European Commission. A consortium of universities, research and clinical facilities, as well as partners from industry carry out an interdisciplinary R&D program across three closely interlinked scientific work packages. These address the development of novel beam imaging and diagnostics systems, studies into treatment optimization including innovative schemes for beam delivery and enhanced biological and physical models in Monte Carlo codes, as well as R&D into clinical facility design and optimization to ensure optimum patient treatment along with maximum efficiency. Selected research highlights from across these work packages will be presented and the impact on hadron therapy facilities around the world discussed.

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TUXGBF2

Higher-Order-Mode Effects in Tesla-Type Superconducting RF Cavities on Electron Beam Quality

HOM, cavity, electron, detector

612

A.H. Lumpkin, N. Eddy, D.R. Edstrom, P.S. Prieto, J. Ruan, R.M. Thurman-Keup
Fermilab, Batavia, Illinois, USA
K. Bishofberger, B.E. Carlsten
LANL, Los Alamos, New Mexico, USA
O. Napoly
CEA/DSM/IRFU, France

Funding: *Work at Fermilab supported by FRA, LLC under Contract No. DE-AC02-07CH11359 with the U.S. Dept. of Energy. **Work at LANL supported by U.S. Dept. of Energy through the LANL/LDRD Program.
We report the direct observations of the correlation of higher order modes (HOMs) generated by off-axis electron beam steering in TESLA-type SCRF cavities and sub-macropulse beam centroid shifts (with the concomitant effect on averaged beam size and emittance). The experiments were performed at the Fermilab Accelerator Science and Technology (FAST) facility using its unique configuration of a PC rf gun injecting beam into two separated 9-cell cavities in series with corrector magnets and beam position monitors (BPMs) located before, between, and after them. The ~100-kHz oscillations with up to 300-μm amplitudes at downstream locations were observed in a 3-MHz micropulse repetition rate beam with charges of 500 and 1000 pC/b, although the effects were much reduced at 100 pC/b. The studies were based on HOM detector circuitry targeting the first and second dipole passbands, rf BPM bunch-by-bunch data, and imaging cameras viewing multi-slit images for emittance assessments at 33 MeV. Initial calculations reproduced a key feature of the phenomena. In principle, these results may be scaled to cryomodule configurations of major accelerator facilities.

Slides TUXGBF2 [3.631 MB]

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TUPAL067

Accelerators Validating Antimatter Physics

proton, antiproton, experiment, electron

1167

C.P. Welsch
The University of Liverpool, Liverpool, United Kingdom
C.P. Welsch
Cockcroft Institute, Warrington, Cheshire, United Kingdom

Funding: This project has received funding from the European Union's Horizon 2020 research and innovation programme under the Marie Skłodowska-Curie grant agreement No 721559.
The Extra Low Energy Antiproton ring (ELENA) will be a critical upgrade to the unique Antiproton Decelerator facility at CERN and is currently being commissioned. ELENA will significantly enhance the achievable beam quality and enable new experiments. To fully exploit the discovery potential of this facility, advances are urgently required in numerical tools that can adequately model beam transport, life time and interaction, beam diagnostics tools and detectors to fully characterize the beam's properties, as well as in novel experiments that exploit the enhanced beam quality that ELENA will provide. These three areas form the scientific work packages of the new pan-European research and training initiative AVA (Accelerators Validating Antimatter physics). The project has received around 4M€ of funding and brings together universities, research centers and industry to train 15 Fellows through research in this area. This contribution presents the research results across AVA's three scientific work packages.

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TUPMF044

First Lasing of the CAEP THz FEL Facility Driven by a Superconducting Accelerator

laser, electron, free-electron-laser, undulator

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.

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TUPMF069

Low Gain FEL Oscillator Option for PETRA IV

undulator, emittance, storage-ring, electron

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.

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TUPMF076

Temporal X-ray Reconstruction Using Temporal and Spectral Measurements

electron, simulation, photon, laser

1440

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.

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TUPMF078

Control of FEL Radiation Properties by Tailoring the Seed Pulses

laser, experiment, electron, simulation

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.

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TUPMF079

An Option to Generate Seeded FEL Radiation for FLASH1

electron, laser, undulator, radiation

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.

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TUPMF080

Progress on Multibunch FEL Performance at FLASH

cavity, operation, controls, accelerating-gradient

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.

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TUPMF085

Status of the sFLASH Experiment

electron, laser, photon, 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.

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TUPMF089

Possible Upgrades of FLASH –- A View from the Accelerator-Perspective

undulator, laser, optics, electron

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.

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TUPMF090

Status of the Superconducting Soft X-Ray Free-Electron Laser FLASH at DESY

laser, operation, undulator, electron

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.

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TUPMK009

Electron Beam Optics for the ASU Compact XFEL

dipole, simulation, electron, laser

1507

C. Zhang, W.S. Graves, M.R. Holl, L.E. Malin
Arizona State University, Tempe, USA
E.A. Nanni
SLAC, Menlo Park, California, USA

Funding: National Science Foundation Division of Physics (Accelerator Science) award 1632780, award 1231306. DOE grant DE-AC02-76SF00515.
Arizona State University (ASU) is pursuing a new concept for a compact x-ray FEL (CXFEL) as a next phase of compact x-ray light source (CXLS). We describe the electron beam optics design for the ASU compact XFEL. In previous experiments we introduced a grating diffraction method to generate a spatially modulated beam. We plan to combine a telescope imaging system with emittance exchange (EEX) to magnify/demagnify the modulated beam and transfer it from transverse modulation into a longitudinal one to make it an ideal seed for phase-coherent XFEL. The simulation results of the beam line setup will be demonstrated. Our first goal is to successfully image the modulated beam with desired magnification then we will investigate various magnification and magnets combinations and optimize aberration correction.

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TUPML011

Experiments Producing Nanopatterned Electron Beams

electron, bunching, experiment, emittance

1553

L.E. Malin, W.S. Graves, J. Spence, K. Weiss, C. Zhang
Arizona State University, Tempe, USA
R.K. Li, E.A. Nanni, X. Shen, S.P. Weathersby, J. Yang
SLAC, Menlo Park, California, USA

Funding: Work supported by NSF awards 1632780 and 1231306, DOE award DE-AC02-76SF00515, and the SLAC UED/UEM Initiative Program Development Fund.
RF photoinjectors are increasingly used to image at the nanoscale in much the same way as a Transmission Electron Microscope (TEM), which are generally sub-MeV energy. We have conducted electron diffraction experiments through a thin membrane of single crystal silicon using both the TEM and photoinjector, and have been able to model and predict the diffraction patterns using the multislice method. A nanopatterned single crystal silicon grating was also imaged in the TEM in the bright field, where all but the direct beam of the diffraction pattern is blocked, giving high contrast spatial modulations corresponding to the 400 nm pitch grating lithographically etched into the silicon. Drawing from our previous multislice calculations, we determined the crystallographic orientation that maximized the contrast in this spatial modulation at the energy of the TEM, giving a bunching factor comparable to a saturated FEL. We report on these key steps toward control of radiation phase and temporal coherence in an FEL.

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TUPML019

Design of Multi-Alkali Photocathode Preparation System for CTFEL Facility

cathode, vacuum, laser, electron

1571

D.X. Xiao, M. Li, Q. Pan, H. Wang, X. Yang
CAEP/IAE, Mianyang, Sichuan, People's Republic of China

The first saturated lasing of the China Academy of Engineering Physics tera-hertz free electron laser (CTFEL) facility has been realized. In order to improve the performance of the CTFEL facility, the multi-alkali photocathode with much longer life-time has been proposed to replace the GaAs photocathode currently used. This paper presents the design of the multi-alkali photocathode preparation system, which consists of three chambers: the suitcase chamber, the preparation chamber, and the loading chamber. The function of each chamber is also discussed.

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TUPML035

FELs Driven by Laser Plasma Accelerators Operated with Transverse Gradient Undulators

undulator, electron, radiation, laser

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

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WEXGBD2

Pulse-by-Pulse Multi-XFEL Beamline Operation with Ultra-Short Laser Pulses

electron, optics, operation, undulator

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 WEXGBD2 [9.708 MB]

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WEYGBD2

Status of the Radiation Damage on the European XFEL Undulator Systems

undulator, radiation, operation, electron

1776

F. Wolff-Fabris, J. Pflüger
XFEL. EU, Schenefeld, Germany
F. Hellberg
Stockholm University, Stockholm, Sweden
F. Schmidt-Föhre
DESY, Hamburg, Germany

The European XFEL GmbH is a new X-ray FEL user facility and started lasing in 2017. Three gap movable SASE Undulator Systems are designed to produce FELs with tunable wavelengths from 0.05 to 5.2nm [*,**]. A total of 91 5-m long undulator segments based on hybrid NdFeB permanent magnet technology were tuned respecting tight specifications. Radiation damage due to machine operation affects the magnetic properties of the segments and the quality of the SASE process. An array of dosimeters based on Radfets [***] and Gafchromic films monitors the absorbed doses in every undulator segment and each SASE system is equipped with a 12mm gap diagnostic undulator (DU) which is magnetically re-measured during machine maintenance weeks. Doses up to 4 kGy have been observed and magnetic field degradation higher than 3% is measured. These results permit to estimate the effects of radiation damage and life expectancy of the Undulator Systems based on the precise K-parameter determination for beam operation. We will present the results of magnetic re-measurements on the Undulator Systems, the details of the effects of radiation damage and future plans to maximize the beam quality and operation.
* M. Altarelli et al., Tech. Design Rep. DESY 2006-097, July 2007.
** E. Schneidmiller et al., Eur. XFEL Tech. Rep. TR-2011-006, Sep. 2011.
*** F. Schmidt-Föhre et al., IPAC-2018 contribution.

Slides WEYGBD2 [3.670 MB]

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WEYGBE2

Applications of Caustic Methods to Longitudinal Phase Space Manipulation

electron, linac, optics, gun

1790

T.K. Charles
The University of Melbourne, Melbourne, Victoria, Australia
T.K. Charles
CERN, Geneva, Switzerland
D. Douglas
JLab, Newport News, Virginia, USA
P.H. Williams
STFC/DL/ASTeC, Daresbury, Warrington, Cheshire, United Kingdom

Longitudinal phase space management is a key feature of recirculating machines. Careful consideration of the longitudinal matching is required not only in order to ensure a high peak current, low energy spread bunch is delivered to the FEL but also to support the deceleration and energy recovery of the spent beam. In a similar manner, longitudinal phase space manipulation can be utilised for pulse shaping in bunch compression, to minimise the influence of CSR-induced emittance growth. In this paper, we present a method for longitudinal phase space matching based upon the avoidance of electron trajectory caustics. Through considering the conditions under which caustics will form, we generate exclusion plots identifying the viable parameter space at numerous positions through beam acceleration and energy recovery. The result is a method for selecting the linear momentum compaction and the higher-order momentum compaction to satisfy the non-caustic condition whilst achieving the bunch compression or lengthening as required.

Slides WEYGBE2 [6.292 MB]

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WEPAF027

Low Q Cavity BPM Study for the Beam Position Measurement of Nanosecond Spaced Electron Bunches

cavity, dipole, electron, coupling

1881

L. Yang, X. He, L.W. Zhang
CAEP/IFP, Mainyang, Sichuan, People's Republic of China
S.S. Cao, Y.B. Leng, L.Y. Yu, R.X. Yuan
SINAP, Shanghai, People's Republic of China

Funding: National natural science foundation of China, 11705184
Low Q cavity BPM is a key to distinguish closely spaced electron bunches allowing precise beam handling for XFEL facilities operating in a multi-bunch mode at high repetition rate up to hundreds MHz. The inter-bunch signal pollution issue becomes significant when bunch separation is down to nanosecond and causes the position detection to be increasingly overestimated. Solely relying on extreme low Q to achieve sufficient decay within bunch interval leads to appreciable interference from non-signal modes due to strong overcoupling of antenna design is required. The error imposed on measured position raises a challenge to meet the goal of high resolution. Alternatively, a concept is proposed to remove the dominant part of signal pollution at the moment of sampling by intentionally shifting the phase of the last bunch signal 90degree respect to that of current bunch signal, where signal sampling is normally taken for nanosecond spaced bunches. This quadrature phase shift is defined by properly choosing the operational frequency of dipole mode regarding to the bunch frequency. A low Q cavity BPM prototype to identify technical challenges and verify this concept is under development in the R&D plan for future XFEL with high repetition rate

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WEPAF035

Coherent Diffraction Radiation Imaging as an RMS Bunch Length Monitor

radiation, target, experiment, detector

1895

J. Wolfenden, R.B. Fiorito, C.P. Welsch
Cockcroft Institute, Warrington, Cheshire, United Kingdom
R.B. Fiorito, C.P. Welsch, J. Wolfenden
The University of Liverpool, Liverpool, United Kingdom
T.H. Pacey, T.H. Pacey
UMAN, Manchester, United Kingdom
A.G. Shkvarunets
UMD, College Park, Maryland, USA

Funding: This work was supported by the EU under Grant Agreement No. 624890 and the STFC Cockcroft Institute core Grant No. ST/G008248/1.
High-resolution bunch length measurement is of the utmost importance for current and future generations of light sources and linacs. It is also key to the optimisation of the final beam quality in plasma-based acceleration. We present progress in the development of a novel RMS bunch length monitor based on imaging the coherent diffraction radiation (CDR) produced by a non-invasive circular aperture. Due to the bunch lengths involved, the radiation produced is in the THz range. This has led to the development of a novel THz imaging system, which can be applied to low energy electron beams. For high energy beams the imaging system can be used as a single shot technique. Simulation results show that the profile of a CDR image of a beam is sensitive to bunch length and can thus be used as a diagnostic. The associated benefits of this imaging distribution methodology over the typical angular distribution measurement are discussed. Plans for experiments conducted at the SwissFEL (PSI, Switzerland), along with plans for future high energy single shot measurements are also presented.

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WEPAF047

Status and Commissioning of the Wire Scanner System for the European XFEL

detector, undulator, MMI, emittance

1919

T. Lensch, S. Liu
DESY, Hamburg, Germany

The European-XFEL (E-XFEL) is an X-ray Free Electron Laser facility located in Hamburg (Germany). The superconducting accelerator for up to 17.5 GeV electrons will provide photons simultaneously to several user stations. Currently 12 Wire Scanner stations are used to image transverse beam profiles in the high energy sections. These scanners provide a slow scan mode which is currently used to measure beam emittance and beam halo distributions. When operating with long bunch trains (>100 bunches) also fast scans are planned to measure beam sizes in an almost nondestructive manner. This paper describes the current installations and the latest developments of the system at European-XFEL. Furthermore, the commissioning status of the system and first results of beam halo studies will be shown.

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WEPAF048

High Resolution and Low Charge Button and Strip-Line Beam Position Monitor Electronics Upgrade at Flash

electron, electronics, laser, operation

1923

B. Lorbeer, N. Baboi, H.T. Duhme, Re. Neumann
DESY, Hamburg, Germany

Historically the FLASH (Free Electron Laser in Hamburg) facility at DESY (Deutsches Elektronen-Synchrotron) in Germany has foreseen operation in a charge range from 1nC-3nC for which a VME based BPM(Beam Position Monitor) system has been in operation since 2005. For a couple of years the standard machine operation has been settled at a few hundreds of pC with the tendency for smaller charges down to 100pC and smaller. The availability and resolution performance of the BPM system at charges below 300pC in many locations along the machine was unsatisfactory. In the last couple of years a new BPM electronic system based on the utca standard has been developed to overcome these limitations. A substantially improved version of the analog frontend and digital electronics has been developed in 2016 and tested successfully. During shutdown works at FLASH in summer 2017 all old button and strip-line BPM electronics has been replaced with the new type of electronics. This paper summarizes the features and performance of the new BPM system, compares the beam jitter free resolution of old and new BPM system and highlights its high single shot resolution of better than 10um at a charge of 15pC.

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WEPAF049

Energy Beam Position Monitor Button Array Electronics for the European XFEL

electron, vacuum, electronics, pick-up

1927

B. Lorbeer, B. Beutner, H.T. Duhme, L. Fröhlich, D. Lipka, D. Nölle
DESY, Hamburg, Germany

The European XFEL(X-Ray Free Electron Laser) at DESY(Deutsches Elektronen-Synchrotron) in Hamburg/Schenefeld started commissioning in early 2017. Before the pulsed electron beam is accelerated to its final energy of 14 GeV, the energy of the bunch can be compressed in three bunch compression chicanes at 130 MeV, 700 MeV and 2400 MeV. The vacuum chamber in these sections is tapered from 40 mm round beam pipe to a 40 cm rectangular shaped vacuum section. A custom made button array type of BPM(Beam position Monitor) is installed in this section with 26 button electrode feed-throughs. The analog and digital readout electronics for this monitor and the first experience with the calibration and operational aspects of this system are presented in this poster.

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WEPAF051

LLRF Operation and Performance at the European XFEL

LLRF, electron, operation, MMI

1934

M. Omet, V. Ayvazyan, J. Branlard, L. Butkowski, M. Hierholzer, M. Killenberg, D. Kostin, L. Lilje, S. Pfeiffer, H. Schlarb, Ch. Schmidt, V. Vogel, N. Walker
DESY, Hamburg, Germany

The European X-ray Free-Electron Laser (XFEL) at Deutsches Elektronen-Synchrotron (DESY), Hamburg, Germany is a user facility providing ultrashort hard and soft X-ray flashes with a high brilliance. All LLRF stations of the injector, covering the normal conducting RF gun, A1 (8 1.3 GHz superconducting cavities (SCs)) and AH1 (8 3.9 GHz SCs), were successfully commissioned by the end of 2015. The commissioning of LLRF stations A2 to A23 (32 1.3 GHz SCs each) in the XFEL accelerator tunnel (XTL) was concluded in June 2017. SASE light was produced in SASE undulator section SA1 and delivered to the first users in September 2017, marking the beginning of regular user operation. The current state of the LLRF systems, the experience gained during operation and the performance achieved in terms of stability and energy reach are presented.

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WEPAF052

High QL and High Gradient CW Operation of Tesla SCRF 9-Cell Cavity

cavity, feedback, operation, controls

1937

K.P. Przygoda, V. Ayvazyan, L. Butkowski, M. Hierholzer, R. Rybaniec, H. Schlarb, Ch. Schmidt, J.K. Sekutowicz
DESY, Hamburg, Germany

In the paper we would like to present Tesla SCRF 9-Cell cavity operated at CW regime with extremely high QL at gradients above 23 MV/m. The design hardware and firmware components as well as developed high level software procedures allows automatic procedure of cavity trip from low to high gradient operation. The microphonics as well as a pendoromotive effects are sensed, identify and applied for cavity detuning correction. The RF and piezo feedbacks performance are demonstrated and preliminary results are briefly discussed.

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WEPAF053

Status and Commissioning of the European XFEL Beam Loss Monitor System

electron, high-voltage, controls, hardware

1940

T. Wamsat, T. Lensch, P.A. Smirnov
DESY, Hamburg, Germany

The European XFEL MTCA based Beam Loss Monitor System (BLM) is composed of about 450 monitors, which are part of the Machine Protection System (MPS). The BLMs detect losses of the electron beam, in order to protect accelerator components from damage and excessive activation, in particular the undulators, since they are made of permanent magnets. Also each cold accelerating module is equipped with a BLM to measure the sudden onset of field emission (dark current) in cavities. In addition some BLMs are used as detectors for wire- scanners. Experience from the already running BLM system in FLASH2 which is based on the same technology, led to a fast implementation of the system in the XFEL. Further firmware and server developments related to alarm generation and handling are ongoing. The BLM systems structure, the current status and the different possibilities to trigger alarms which stop the electron beam will be presented.

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WEPAL012

Measurements with the ELI-NP Cavity Beam Position Monitor Read-out Electronics at FLASH

electron, cavity, instrumentation, electronics

2169

G. Franzini, D. Pellegrini, M. Serio, A. Stella, A. Variola
INFN/LNF, Frascati (Roma), Italy
B.B. Baricevic, M. Cargnelutti
I-Tech, Solkan, Slovenia
D. Lipka
DESY, Hamburg, Germany
M. Marongiu
INFN-Roma, Roma, Italy
A. Mostacci
Sapienza University of Rome, Rome, Italy

The Extreme Light Infrastructure - Nuclear Physics Gamma Beam Source (ELI-NP GBS) will be installed and commissioned starting within the next year in Magurele, Romania. It will generate gamma beam through Compton back-scattering of a recirculated laser and a multi-bunch electron beam, produced by a 720 MeV LINAC. In order to obtain bunch by bunch position measurements, four cavity beam position monitors (cBPM) near the two interaction points are foreseen. Extensive tests on the cBPM read-out electronics, recently developed by Instrumentation Technologies and acquired for ELI-NP GBS, were performed in laboratory at INFN-LNF and at FLASH in DESY, during the user operation. In the latter case, three cBPMs installed along the LINAC, with similar features as the ones of ELI-NP GBS, were used as measuring devices and signal sources for the read-out electronics under test. We present here the measurements collected and the related analysis, with a particular focus on the beam position measurement resolution.

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WEPAL026

High Repetition Rate, Single-Shot Electro-Optical Monitoring of Longitudinal Electron Bunch Dynamics Using the Linear Array Detector KALYPSO

electron, storage-ring, laser, radiation

2216

G. Niehues, E. Blomley, M. Brosi, E. Bründermann, M. Caselle, S. Funkner, A.-S. Müller, M.J. Nasse, L. Rota, M. Schuh, P. Schönfeldt, M. Weber
KIT, Eggenstein-Leopoldshafen, Germany
N. Hiller
PSI, Villigen PSI, Switzerland

Funding: This work is funded by the BMBF contract numbers: 05K13VKA and 05K16VKA.
High repetition rate diagnostics are required when detecting single-shot electro-optical (EO) bunch profiles. The KIT storage ring KARA (KArlsruhe Research Accelerator) is the first storage ring in the world that has a near-field EO bunch-profile monitor in operation. By imprinting longitudinal electron bunch profiles onto chirped laser pulses, single-shot detection is feasible. However, limitations of available detection systems are challenging: The constraints are either given by the repetition rate or the duration of the consecutive acquisitions. Two strategies can overcome these limitations: Based on the photonic time-stretch method, the ps laser pulses can be stretched to the ns range using km long fibers. The readout with a high-bandwidth oscilloscope then enables a single-shot detection at high repetition rates. The other strategy is the development of dedicated ultra-fast photodetector arrays allowing direct detection of the ps pulses at MHz repetition rates. We developed KALYPSO, a linear detector array with a DAQ allowing to record high data-rates over long time scales. Here, we present recent results of studies of the longitudinal electron bunch dynamics using KALYPSO.

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WEPAL045

An Electrostatic Fixed-Slit Emittance Measurement System

emittance, cathode, electron, focusing

2274

J.W. Lewellen, H.L. Andrews, R.L. Fleming, K.E. Nichols, E.I. Simakov
LANL, Los Alamos, New Mexico, USA

Funding: Los Alamos National Laboratory LDRD Program
The emittance of a field emission cathode can be difficult to measure close to the emitter, due to the high average current density of the beam and the potential for desorbed material from an imaging screen to contaminate the cathode. We present the design for a dual fixed-slit emittance measurement system for a field emitter cathode, implemented using electrostatic deflecting plates. Results from fabrication and initial testing will be presented.

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WEPAL070

HLS System to Measure the Location Changes in Real Time of PAL-XFEL Devices

alignment, linac, real-time, survey

2345

H. J. Choi, J.H. Han, H.-S. Kang, S.H. Kim, H.-G. Lee, S.B. Lee
PAL, Pohang, Kyungbuk, Republic of Korea

All components of PAL-XFEL (Pohang Accelerator Laboratory's X-ray free-electron laser) were completely installed in December 2015, and Hard X-ray 0.1nm lasing achieved through its beam commissioning test and machine study on March 16, 2017. The beam line users has been performing various tests including pump-probe X-ray scattering, time-resolved x-ray liquidography, etc in the hard x-ray beam line since March 22. The energy and flux of x-ray photon beam generated from XFEL and synchronization timing should be stable to ensure successful time-resolved tests. Several parts that comprise the large scientific equipment should be installed and operated at precise three-dimensional location coordinates X, Y, and Z through survey and alignment to ensure their optimal performance. As time goes by, however, the ground goes through uplift and subsidence, which consequently changes the coordinates of installed components and leads to alignment errors ΔX, ΔY, and ΔZ. As a result, the system parameters change, and the performance of the large scientific equipment deteriorates accordingly. Measuring the change in locations of systems comprising the large scientific equipment in real time would make it possible to predict alignment errors, locate any region with greater changes, realign components in the region fast, and shorten the time of survey and alignment. For this purpose, a HLS's (hydrostatic leveling sensor) with 0.2um of resolution are installed and operated in a waterpipe of total length 1km in the PAL-XFEL building. This paper is designed to introduce the operating principle of the HLS, the installation and operation of the HLS system, and how to utilize the HLS system in order to ensure beam stabilization.

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WEPMF021

Magnet Design Considerations for an Ultralow Emittance Canadian Light Source

quadrupole, lattice, emittance, storage-ring

2413

L.O. Dallin, D. Bertwistle
CLS, Saskatoon, Saskatchewan, Canada

The strong focusing requirements for ultralow emittance light sources result in high field magnets that are very close together. High fields are readily achieved by using small magnet gaps. This is possible due to the small beam sizes involved. Reduction in the physical aperture and the reduction in the good field region requirements results in magnets with compact transverse dimensions. The very strong focusing of the magnets results in very small drift spaces between the various magnetic elements. To keep these drift spaces clear magnets with recessed coils have been studied. In such magnets the coils do not stick out beyond the end of the magnet yoke in the longitudinal direction. By placing the coils on the outer yoke loss of efficiency can be avoided while maintaining good control of the higher order field harmonics. This is very well suited for quadrupole magnets where only two coils are required. Possible designs for gradient dipoles and sexutpoles are also considered.

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WEPMF053

XFEL Modulators with Pulse Cables

operation, klystron, linac, radiation

2487

H.-J. Eckoldt, S. Choroba, T. Grevsmühl, A. Hauberg, J. Havlicek, N. Heidbrook, K. Machau, N. Ngada
DESY, Hamburg, Germany
M. Frei, S.G. Keens, T.H. Strittmatter
Ampegon AG, Turgi, Switzerland
H. Leich
DESY Zeuthen, Zeuthen, Germany

The modulators of the European XFEL produce high voltage, at the 10kV level, having a power of up to 16.8 MW for 1.54 ms. The operation frequency of the super-conducting inac is 10 Hz. The series production of the 29 modulators started in 2012. The first modulator began operation in 2014 and the start of linac was beginning 2017. The R&D phase for the modulators started directly with the development of superconducting cavities. Besides the pulse generation, the modulator had to suppress the 10 Hz repetition rate in order not to disturb the grid. Another unique demand was the development of pulse cables. Since the power RF had to be generated in the tunnel, the klystrons were installed near the cavities. However, the modulators had to be installed outside of the tunnel for space, maintenance reasons and radiation concerns. This transmission of high power pulses via long cables is unique in the world and the suppression of EMI effects was mandatory. During the first year operation no EMI disturbances of other systems were detected and the modulator system works as expected.

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WEPMF056

Cs2Te Photocathode Lifetime at Flash and European XFEL

cathode, laser, gun, operation

2496

S. Lederer, S. Schreiber
DESY, Hamburg, Germany

The photo-injectors of FLASH and the European XFEL at DESY (Hamburg, Germany) use Cs2Te photocathodes. In this contribution we give an update on the lifetime and quantum efficiency of the cathodes operated in both facilities. Cathode #680.1 was operated at the European XFEL from the injector commissioning to the first user run for over 700 days. At FLASH cathode #73.3 has been operated with a record of more than 1000 days.

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WEPMF058

Anomaly Detection for Cavity Signals - Results from the European XFEL

cavity, flattop, beam-loading, simulation

2502

A.S. Nawaz, S. Pfeiffer
DESY, Hamburg, Germany
G. Lichtenberg
HAW, Hamburg, Germany
P. Rostalski
Institute for Electrical Engineering in Medicine, Lübeck, Germany

The data throughput of the European XFEL DAQ is about 1.5 Gb/s. Data depicting the cavity signal behavior is currently only saved manually. This either happens, when cavity tests are being performed, or an operator detects a fault in the cavity system, that has to be further investigated. Those instances of interest are neither systematically nor automatically stored. It can therefore be assumed that unwanted or degraded cavity behavior is detected late or not at all. It is proposed to change the focus from detecting known faults (such as quenches) to additionally detect anomalies in the cavity system behavior. In order to detect anomalies in the cavity signals, an algorithm is proposed using a cavity model. It aims on finding those data sets, which diverge from the nominal cavity behavior, saving those instances for later analysis. The nominal behavior is defined by the cavity electromagnetic resonance model with beam loading as well as the model for the mechanical oscillations due to the Lorentz Forces. By using such an approach, the detection of anomalies, as well as faults could be automated. This contribution aims to summarize the influence of beam loading on the detection and gives examples for anomalies that were found in several cavities.

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WEPMF067

A High Gradient Solution for Increasing the Energy of the FERMI Linac

linac, electron, wakefield, laser

2525

C. Serpico, I. Cudin, S. Di Mitri, N. Shafqat, M. Svandrlik
Elettra-Sincrotrone Trieste S.C.p.A., Basovizza, Italy
M. Bopp, R. Zennaro
PSI, Villigen PSI, Switzerland

FERMI is the seeded Free Electron Laser (FEL) user facility at Elettra laboratory in Trieste, operating in the VUV to soft X-rays spectral range. In order to extend the FEL spectral range to shorter wavelengths, a feasibility study for increasing the Linac energy from 1.5 GeV to 1.8 GeV is actually going on. The design of new S-band accelerating structures, intended to replace the present Backward Travelling Wave sections, is presented. Such design is tailored for high gradient operation, low breakdown rates and low wakefield contribution. In this paper, we will also present the first, short prototype that has been built in collaboration with Paul Scherrer Institute (PSI).

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WEPMK008

In-Depth Analysis of the Vertical Test Results of the Third-Harmonic Cavities for the E-XFEL Injector

cavity, experiment, feedback, SRF

2644

M. Bertucci, A. Bignami, A. Bosotti, J.F. Chen, C.G. Maiano, P. Michelato, L. Monaco, R. Paparella, P. Pierini, D. Sertore
INFN/LASA, Segrate (MI), Italy
C.G. Maiano, P. Pierini
ESS, Lund, Sweden
C. Pagani
Università degli Studi di Milano & INFN, Segrate, Italy

The results of the vertical tests performed at LASA on the 3.9 GHz third-harmonic cavities for the E-XFEL injector are here discussed. Analysis of experimental data allows to confirm that such high frequency cavity, prepared with standard BCP treatment and 800°C annealing treatment, suffers an intrinsic performance limitation at around 22 MV/m (@ 2 K) due to a global thermal dissipation mechanism. A quantitative interpretation of the high field Q slope is also presented according to the latest theoretical models of field-dependent surface resistance.

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WEPMK010

LCLS-II Cryomodules Production at Fermilab

cryomodule, cavity, vacuum, controls

2652

T.T. Arkan, J.N. Blowers, C.M. Ginsburg, C.J. Grimm, J.A. Kaluzny, A. Lunin, Y.O. Orlov, K.S. Premo, R.P. Stanek, G. Wu
Fermilab, Batavia, Illinois, USA

Funding: DOE
LCLS-II is a planned upgrade project for the linear coherent light source (LCLS) at SLAC. The LCLS-II linac will consist of thirty-five 1.3 GHz and two 3.9 GHz superconducting RF continuous wave (CW) cryomodules that Fermilab and Jefferson Lab are currently producing in collaboration with SLAC. The LCLS-II 1.3 GHz cryomodule design is based on the European XFEL pulsed-mode cryomodule design with modifications needed for CW operation. Two prototype cryomodules had been assembled and tested. After prototype cryomodule tests, both laboratories have increased cryomodule production rate to meet the challenging LCLS-II project installation schedule requirements of approximately one cryomodule per month per laboratory. Fermilab is at half point for the production, meaning that 6 cryomodules are fully assembled and tested. This paper presents Fermilab Cryomodule Assembly Facility (CAF) infrastructure for the LCLS-II cryomodules assembly, production experience at the half point emphasizing the challenges and mitigations.

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WEPML008

Tuner Testing of a Dressed 3.9 GHz Cavity for LCLS-II at Fermilab

cavity, SRF, operation, background

2690

J.P. Holzbauer, S. Aderhold, T.N. Khabiboulline, Y.M. Pischalnikov, W. Schappert, J.C. Yun
Fermilab, Batavia, Illinois, USA
C. Contreras-Martinez
FRIB, East Lansing, USA

Funding: This manuscript has been authored by Fermi Research Alliance, LLC under Contract No. DE-AC02-07CH11359 with the U.S. Department of Energy, Office of Science, Office of High Energy Physics.
Fermilab is responsible for the design of the 3.9 GHz cryomodule for LCLS-II. Integrated acceptance testing of a dressed 3.9 GHz cavity for the LCLS-II project has been done at the Fermilab Horizontal Test Stand. This test included a slim blade tuner (based on INFN & XFEL designs) with integrated piezoelectric fast/fine tuner. This paper will present results of the mechanical setup, cold testing, and cold function of this tuner including fast and slow tuner range, sensitivity, and hysteresis.

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WEPML023

Design and Test Results of the 3.9 GHz Cavity for LCLS-II

cavity, radiation, cryomodule, operation

2730

N. Solyak, S. Aderhold, S.K. Chandrasekaran, C.J. Grimm, T.N. Khabiboulline, A. Lunin, O.V. Prokofiev, G. Wu
Fermilab, Batavia, Illinois, USA

The LCLS-II project uses sixteen 3.9 GHz superconduct-ing cavities to linearize energy distribution before the bunch compressor. To meet LCLS-II requirements origi-nal FNAL design used in FLASH and XFEL was signifi-cantly modified to improve performance and provide reliable operation up to 16 MV/m in cw regime [1-3]. Four prototype cavities were built and tested at vertical cryo-stat. After dressing, one cavity was assembled and tested at horizontal cryostat as part of design verification pro-gram. All auxiliaries (magnetic shielding, power and HOM couplers, tuner) were also re-designed and tested with this cavity. In this paper we will discuss cavity and coupler design and test results.

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THXGBD2

Overview of Undulator Concepts for Attosecond Single-Cycle Light

electron, undulator, laser, bunching

2878

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 THXGBD2 [1.758 MB]

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THYGBE1

Applying Artificial Intelligence to Accelerators

controls, feedback, electron, network

2925

A. Scheinker, R.W. Garnett, D. Rees
LANL, Los Alamos, New Mexico, USA
D.K. Bohler
SLAC, Menlo Park, California, USA
A.L. Edelen, S.V. Milton
CSU, Fort Collins, Colorado, USA

Particle accelerators are being designed and operated over a wide range of complex beam phase space distributions. For example, the Linac Coherent Light Source (LCLS) upgrade, LCLS-II, is considering complex schemes such as two-color operation [1], while the plasma wake field acceleration facility for advanced accelerator experimental tests (FACET) upgrade, FACET-II, is planning on providing custom tailored current profiles [2]. Because of uncertainty due to limited diagnostics and time varying performance, such as thermal drifts, as well as collective effects and the complex coupling of large numbers of components, it is impossible to use simple look up tables for parameter settings in order to quickly switch between widely varying operating ranges. Several forms of artificial intelligence are currently being investigated in order to enable accelerators to quickly and automatically re-adjust component settings without human intervention. In this work we discuss recent progress in applying neural networks and adaptive feedback algorithms to enable automatic accelerator tuning and optimization.
[1] A. A. Lutman et al., Nat. Photonics 10.11, 745 (2016).
[2] V. Yakimenko et al., IPAC2016, Busan, Korea, 2016.

Slides THYGBE1 [14.256 MB]

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THPAF006

Simulations of Cooling Rate and Diffusion for Coherent Electron Cooling Experiment

electron, simulation, kicker, bunching

2957

J. Ma, V. Litvinenko, G. Wang
BNL, Upton, Long Island, New York, USA
V. Litvinenko
Stony Brook University, Stony Brook, USA

Start-to-end numerical simulations have been performed using the code SPACE and GENESIS for the single pass of gold ions through the coherent electron cooling (CeC) device installed in the Relativistic Heavy Ion Collider (RHIC) at Brookhaven National Laboratory (BNL). Cooling rate of CeC experiment has been predicted using off-reference energy ions in a finite Gaussian electron beam through a realistic beam-line, in which settings of quadrupoles and free-electron laser (FEL) device are relevant to BNL RHIC.

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THPAF033

Degradation of Electron Beam Quality for a Compact Laser-Based FEL

electron, emittance, laser, space-charge

3029

A.Y. Molodozhentsev, L. Pribyl
Czech Republic Academy of Sciences, Institute of Physics, Prague, Czech Republic
K.O. Kruchinin
ELI-BEAMS, Prague, Czech Republic

Laser wake field acceleration (LWFA) mechanism allows to produce extremely short electron bunches of a few fs length with the energy up to a few GeV in extremely compact geometries providing unique electron beam parameters, in particular, transverse beam emittance (order of 1pi mm mrad), extremely short bunch length and high beam charge (up to 100pC) . This novel acceleration method therefore opens a new way to develop compact 'laser-based' FELs. In the frame of this report we analyze effects, which lead to degradation of an electron beam quality. The chromatic and collective effects are analyzed for a compact dedicated electron beam line to transport the electron beam to an undulator. In addition, the SASE FEL performance has been discussed taking into consideration the degradation of the electron beam quality.

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THPAK010

Optimization on the Optical Resonator of CTFEL

GUI, radiation, coupling, electron

3228

X.J. Shu, Y.H. Dou
Institute of Applied Physics and Computational Mathematics, People's Republic of China
M. Li, Z. Xu, Y. Xu, X. Yang
CAEP/IAE, Mianyang, Sichuan, People's Republic of China

Funding: Program for the National Science Foundation of China (Grant No. 11105019) and the National Science Device Exploitation Foundation of China (Grant No. 2011YQ130018).
A high power THz free electron laser (FEL) facility is under construction at China Academy of Engineering Physics (CTFEL) since October, 2011. The radiation frequency of the FEL facility will be tuned in range of 1~3 THz and the average output power is about 10 W. The system mainly consists of a GaAs photoemission DC gun, superconductor accelerator, the hybrid wiggler, optical cavity. The first lasing is obtained on Aug. 29, 2017. The optical resonator of CTFEL is optimized to ensure wavelength tunable in a wide range and high power operation. The FEL power strongly depends on the performance of the optical resonator including output efficiency, gain and round-trip loss. The optical resonator consists of metal-coated reflect mirror, the center-hole output mirror, waveguide. The influence of waveguide and Rayleigh length on the quality of optical cavity is evaluated by the 3D-OSIFEL code. The waveguide size, mirror curvature radius, output hole radius is optimized to different frequencies between 1 THz to 3 THz.

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THPAK064

Theoretical Modeling of Electromagnetic Field from Electron Bunches in Periodic Wire Medium

radiation, simulation, electron, lattice

3376

S.S. Chuchurka, A.I. Benediktovitch
BSU, Minsk, Belarus, Belarus
S.N. Galyamin, V.V. Vorobev
Saint Petersburg State University, Saint Petersburg, Russia
A. Halavanau
Northern Illinois University, DeKalb, Illinois, USA

Funding: Work supported by the Grant from Russian Foundation for Basic Research (No. 17-52-04107).
The interaction of relativistic electrons with periodic structures results in radiation by a number of mechanisms. In case of crystals one obtains parametric X-ray radiation, its frequency is determined by distance between crystallographic planes and direction of electron beam. If instead of crystal one considers a periodic structure of metallic wires with period of the order of mm, one can expect emission of THz radiation. In the present contribution we consider theoretical approaches for modeling of the distribution of electromagnetic field from electron bunches in lattice formed by metallic wires. The analytical description is possible for the case of wires with small radius, the range of validity is checked by numerical simulations. The intensity of radiation will be significantly increased if the electrons in the bunch could radiate coherently. Two possibilities will be discussed: the prebunching of the beam and the self-modulation of the beam due to interaction with radiated field.

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THPAK074

Beam Manipulation Using Self-Induced Fields in the SwissFEL Injector

wakefield, electron, experiment, laser

3401

S. Bettoni, P. Craievich, R. Ganter, P. Heimgartner, H. Jöhri, F. Marcellini, S. Reiche
PSI, Villigen PSI, Switzerland

Several possibilities of manipulating the electron beam using sources of wakefield are being explored. Wakefield have been successfully used to remove or enhance the energy chirp residual from the magnetic compression to control the free electron laser bandwidth (dechirper), to linearize the compressed beam (linearizer), to generate more bunches to produce two color mode, and to perform experiments of wakefield acceleration. At the SwissFEL injector we plan to install 2 m long system to accommodate sources of wakefield with different periodicities, each of them associated with one of the discussed beam manipulation. In this paper we summarize the design and the characterization of the system and the planned activities.

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THPAK136

Wide-Ranging Genetic Research of Matching Line Design for Plasma Accelerated Beams with GIOTTO

plasma, emittance, electron, target

3561

M. Rossetti Conti
Universita' degli Studi di Milano & INFN, Milano, Italy
A. Bacci, A.R. Rossi
Istituto Nazionale di Fisica Nucleare, Milano, Italy
A. Giribono, C. Vaccarezza
INFN/LNF, Frascati (Roma), Italy

GIOTTO is a code based on a Genetic Algorithm, being used in the field of particles accelerators for some years*-***. Its main use concerns beam-dynamics optimizations for low energy linacs, or injectors, where the beam space-charge plays an important role on its dynamics. Typical optimizations regard the Velocity Bunching technique or, more generally, the emittance and energy spread minimization. Recent improvements in GIOTTO, here discussed, have added the important capability to solve problems with a wide research domain, making GIOTTO able to design a beam Transfer Line (TL) from scratch****. The code, taking as input the TL length and the optics elements, can define the correct lattice of the line that transports and matches the beam from the linac to the undulators of an FEL, finding the right gradients, positions and dimensions for the optics elements by exploring the parameters values in selected ranges. Further, the introduction of Twiss parameters into the fitness function makes GIOTTO a powerful tool in the design of highly different beam lines. Lastly, a new routine for the statistical analysis of parameters jitters effects on the beam is under development.
*Bacci et al, NIM-B, 263, 488 (2007)
**Bacci et al, presented at PAC'07, THPAN031
***Bacci et al, presented at IPAC'16, WEPOY039
****Rossetti Conti et al, NIM-A (2018, in press)

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THPAK138

Development of Efficient Tree-Based Computation Methods for the Simulation of Beam Dynamics in Sparsely Populated Phase Spaces

simulation, electron, bunching, HOM

3569

Ph. Amstutz
University of Hamburg, Institut für Experimentalphysik, Hamburg, Germany
M. Vogt
DESY, Hamburg, Germany

Collective instabilities pose a major threat to the quality of the high brightness electron beams needed for the operation of a free electron laser. Multi-stage bunch compression schemes have been identified as a possible source of such an instability. The dispersive sections in these compressors translate energy inhomogeneities within the bunch into longitudinal charge density inhomogeneities. In conjunction with a collective force driving locally density-dependent energy modulations this leads to intricate longitudinal beam dynamics. As a consequence of the thin shape those bunches form in the longitudinal phase space, efficient simulation of such systems is not straight forward. At high resolutions, the numerical representation of the phase space density on a uniform grid is too wasteful, due to the large unpopulated phase space regions. In this contribution we present advances made in the development of a simulation code that addresses the problem of sparsely populated phase spaces by means of quadtree domain decomposition. A focus lies on the explanation of the underlying tree data structure.

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THPAL068

Status of the Polarix-TDS Project

electron, undulator, status, klystron

3808

P. Craievich, M. Bopp, H.-H. Braun, R. Ganter, T. Kleeb, M. Pedrozzi, E. Prat, S. Reiche, R. Zennaro
PSI, Villigen PSI, Switzerland
R.W. Aßmann, F. Christie, R.T.P. D'Arcy, U. Dorda, M. Foese, P. González Caminal, M. Hoffmann, M. Hüning, R. Jonas, O. Krebs, S. Lederer, V. Libov, B. Marchetti, D. Marx, J. Osterhoff, F. Poblotzki, M. Reukauff, H. Schlarb, S. Schreiber, G. Tews, M. Vogt, A. Wagner
DESY, Hamburg, Germany
N. Catalán Lasheras, A. Grudiev, G. McMonagle, W. Wuensch
CERN, Geneva, Switzerland

A collaboration between DESY, PSI and CERN has been established to develop and build an advanced modular X-band transverse deflection structure (TDS) system with the new feature of providing variable polarization of the deflecting force. This innovative CERN design requires very high manufacturing precision to guarantee highest azimuthal symmetry of the structure to avoid the deterioration of the polarization of the streaking field. Therefore, the high-precision tuning-free production process developed at PSI for the C-band and X-band accelerating structures will be used for the manufacturing. We summarize in this paper the status of the production of the prototype and the waveguide networks foreseen in the different facilities.

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THPAL084

An X-Band Lineariser for the CLARA FEL

cavity, simulation, wakefield, klystron

3848

L.S. Cowie, A.D. Brynes, J.K. Jones, A.E. Wheelhouse, P.H. Williams
STFC/DL/ASTeC, Daresbury, Warrington, Cheshire, United Kingdom
R. Apsimon, G. Burt, W.L. Millar
Cockcroft Institute, Lancaster University, Lancaster, United Kingdom
Ö. Mete
UMAN, Manchester, United Kingdom
A.J. Moss
STFC/DL, Daresbury, Warrington, Cheshire, United Kingdom

The CLARA FEL at Daresbury Laboratory will employ four S-band linacs to accelerate electron bunches to 250 MeV/c. In order to compress the bunch sufficiently to achieve peak currents suitable for FEL lasing, one must compensate for curvature imprinted on the longitudinal phase space of the bunch. For CLARA a harmonic RF linearization system has been designed to achieve this requirement. The linearization will be achieved by an X-band travelling wave cavity of the PSI/CERN design, which incorporates wake-field monitoring of the bunch position. A five-axis mover will align the cavity to the beam axis. Pulse compression of a 6 MW klystron pulse will provide the required power to achieve a 30 MV/m operational gradient.

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THPAL101

Longitudinal Effects of Trapped Homs in Shanghai Coherent Light Facility

cavity, HOM, linac, impedance

3872

J.J. Guo, Q. Gu, H.T. Hou, J.H. Tan, M. Zhang
SINAP, Shanghai, People's Republic of China

Funding: Shanghai Institute of Applied Physics, Chinese Academy of Sciences
Shanghai Coherent Light Facility (SCLF), a superconducting accelerated structure-baesd FEL device, is now under development at Shanghai Institute of Applied Physics, Chinese Academy of Sciences. We investigate effects of cryogenic losses caused by trapped longitudinal high order modes (HOM). Results of calculations are presented for losses caused by HOMs excitation in the acceleration RF system of the continues-wave (CW) linac of SCLF.

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THPAL102

Design a High Power Pulse Transformer for C-band Klystron Modulator

flattop, klystron, high-voltage, plasma

3875

Y.F. Liu, Z.H. Chen, M. Gu, Y. Wu, Q. Yuan, X.X. Zhou
SINAP, Shanghai, People's Republic of China

Shanghai soft X-ray Free Electron Lasers (SXFEL) first uses C band accelerator structure to accelerate electrons at SINAP. SXFEL is an X-ray free electron laser facility, which requests very stable amplitude stability and very tight tolerances of phase jitter. 50MW C-band klystron and 110MW modulator is used to provide power supply for accelerator structure. Typical specifications of the modulator are peak beam voltage 350KV, peak beam current 320A, 10Hz repetition rate, 3us flat-top pulse width. In order to meet these demands, we developed a reliable and stable high power pulse transformer. In this paper, the analysis and design of high power pulse transformer for C band klystron modulator are presented. The methods of shortening rise time, diminishing droop and diminishing flat top oscillation are highlighted. Detailed design, simulation and relevant experimental results are given. The relevant experiments show that this pulse transformer can meet the requirement of 50MW C band klystron.

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THPAL118

Critical Fields of SRF Materials

niobium, cavity, interface, superconductivity

3921

T. Junginger
TRIUMF, Vancouver, Canada
T. Prokscha, Z. Salman, A. Suter
PSI, Villigen PSI, Switzerland
A-M. Valente-Feliciano
JLab, Newport News, Virginia, USA

Nb3Sn and NbTiN are two potential alternative materials to niobium for superconducting RF cavities. In this study direct measurements of the magnetic penetration depth using the low energy muon spin rotation technique are presented, from which the lower critical field and the superheating field are derived. Comparison with RF data confirms that the lower critical field is not a fundamental limitation and predict a potential performance clearly exceeding current state of the art of niobium technology if the superheating field can be achieved. As a potential pathway to avoid premature vortex penetration and reaching the superheating field it is suggested to use a bilayer structure with the outer layer having a larger magnetic penetration depth.

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THPAL128

Autonomous Topography Detection and Traversal for an Inspection Robot Within the Beamline of Particle Accelerators

vacuum, experiment, kicker, heavy-ion

3943

N. Schweizer
Technische Universität Darmstadt (TU Darmstadt, RMR), Darmstadt, Germany
I. Pongrac
GSI, Darmstadt, Germany

Particle accelerators feature ultra-high vacuum pipe systems with unique topography, i.e. with a multitude of different vacuum chambers of varying dimensions and varying pipe apertures. In order to be able to examine the interior of the entire vacuum system, even those parts which are not accessible without disassembling large parts of the accelerator, a semi-autonomous robot is being developed which shall traverse and visually inspect the vacuum system of particle accelerators. We present a generic concept based on distance sensors for the inspection robot to detect steps between vacuum chambers and gaps in the beamline. Movement strategies to autonomously overcome these basic obstacles are introduced. For evaluation we use simulations of ideal environments with flat surfaces as well as realistic beam pipe environments of the SIS100 particle accelerator. Additionally, a prototype of our robot concept confirms the implementation of all maneuvers. Results show that obstacles of previously unknown dimensions can be detected and reliably traversed.

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THPAL142

Surface Characterization of NbTiN Films for Accelerator Applications

site, SRF, detector, lattice

3975

D.R. Beverstock, M.J. Kelley, C.E. Reece, J.K. Spradlin, A-M. Valente-Feliciano
JLab, Newport News, Virginia, USA

Funding: Work supported by Jefferson Science Associates, LLC under U.S. DOE Contract No. DE-AC05-06OR23177.
The development of next-generation SRF cavities requires the deployment of innovative material solutions with RF performance beyond bulk Nb. Theoretical interest has stimulated efforts to grow and characterize thin multi-layer superconductor/insulator/superconductor (SIS) structures for their potential capability of supporting otherwise inaccessible surface magnetic fields in SRF cavities *. The ternary B1-compound NbTiN is among the candidate superconducting materials for SIS structures. Single crystal NbTiN films with thicknesses below 15 nm are also of interest for the development of high resolution, high sensitivity (SNSPD) detectors for particle physics application. Using DC reactive magnetron sputtering, NbTiN can be deposited with nominal superconducting parameters. This contribution presents the on-going material surface and superconducting properties characterization in order to optimize the NbTiN films for each application.
* A Gurevich, "Maximum screening fields of superconducting multilayer structures", AIP ADVANCES 5, 017112 (2015)

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THPAL153

High Power Test of the S-Band Spherical Pulse Compressor at Tsinghua University

cavity, coupling, polarization, klystron

4008

P. Wang, D.Z. Cao, H.B. Chen, C. Cheng, J. Shi, Z.H. Wang, H. Zha
TUB, Beijing, People's Republic of China

We designed, fabricated and high power tested an S-band spherical pulse compressor for the high-power test facility at Tsinghua University. The pulse compressor comprises a spherical resonant cavity with an unloaded quality factor of 100, 000 and an RF polarizer with two rectangular ports and a circular port. To achieve high efficiency and large power gain, the coupling coefficient was optimized to 8 with input pulse length of 3.6 us and compression ratio of 12. After conditioning the RF system, the pulse compressor generated RF pulses with peak power of more than 400MW. And during the operation, the pulse compressor has very low breakdown rate and was extremely stable.

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THPMF012

Tapered Flying Radiofrequency Undulator

undulator, electron, simulation, ECR

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%).

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THPMF016

Design of a Terahertz Radiation Source for Pump-Probe Experiments

bunching, undulator, radiation, electron

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.

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THPMF022

Study of Possible Beam Losses After Post-Linac Collimation at European XFEL

undulator, radiation, simulation, vacuum

4092

S. Liu, W. Decking
DESY, Hamburg, Germany
F. Wolff-Fabris
XFEL. EU, Schenefeld, Germany

The European XFEL has been operating with the undulator beam line SASE1 and SASE3 since April 2017 and February 2018, respectively. Despite of the fact that the post-linac collimation has collimated the beam halo to ~20 σ level*, relative high radiation doses have been measured especially in the diagnostic undulator (DU) section**. In order to find the sources of beam losses after post-linac collimation, BDSIM simulations have been performed. In this paper, we will first present the possible losses generated by the wire scanners upstream of the undulators during a scan. The simulation results will be compared with the measured doses along SASE1 and SASE3 undulators. Based on the simulation results, we will estimate the frequency for wire scanner opera-tions. Besides, the simulations with large extension of beam halo hitting the vacuum chamber aperture transition will also be presented. Finally, other possible radiation dose sources will be discussed.
* S. Liu et al., in Proc. of FEL 2017, Santa-Fe, USA, Aug. 2017, paper TUP003.
** F. Wolff-Fabris et al.,IPAC-2018 contribution.

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THPMF031

In-Vacuum APPLE II Undulator

vacuum, undulator, cryogenics, operation

4114

J. Bahrdt, W. Frentrup, S. Grimmer, C. Kuhn, C. Rethfeldt, M. Scheer, B. Schulz
HZB, Berlin, Germany

APPLE II undulators are widely used in many synchrotron radiation facilities for the generation of arbitrarily polarized light, because they provide the highest magnet fields among all planar variably polarizing permanent magnet undulators (PMUs). So far, in-vacuum permanent magnet undulators (IVUs) have a fixed polarization, either planar or elliptical / helical. A variably polarizing in-vacuum undulator was never built due to the engineering challenges. We present the design of a new in-vacuum APPLE II, which will extend the photon energy range to tender X-rays in the 1.7 GeV storage ring BESSY II.

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THPMF050

High-Efficient XFELO Based on Optical Resonator with Self-Modulated Q-Factor

undulator, laser, coupling, electron

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.

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THPMF058

The MariX source (Multidisciplinary Advanced Research Infrastructure with X-rays)

electron, cavity, gun, radiation

4199

V. Petrillo, N. Piovella
Universita' degli Studi di Milano, Milano, Italy
A. Bacci, F. Castelli, S. Cialdi, C. Curatolo, I. Drebot, D. Giannotti, D. Giove, C. Meroni, A.R. Rossi, L. Serafini, M. Statera, V. Torri
Istituto Nazionale di Fisica Nucleare, Milano, Italy
A. Bosotti, F. Broggi, F. Groppi, P. Michelato, L. Monaco, R. Paparella, D. Sertore
INFN/LASA, Segrate (MI), Italy
R. Calandrino, A. Delvecchio
HSP, Milan, Italy
F. Camera, S. Coelli, G. Onida, B. Paroli, L. Perini, F. Prelz, M. Rossetti Conti, F. Tomasi
Universita' degli Studi di Milano & INFN, Milano, Italy
P. Cardarelli, M. Gambaccini, G. Paternò, A. Taibi
INFN-Ferrara, Ferrara, Italy
A. Castoldi, G. Ghiringhelli, C. Guazzoni, M. Moretti, E. Pinotti
Polytechnic of Milan, Milano, Italy
S. Di Mitri
Elettra-Sincrotrone Trieste S.C.p.A., Basovizza, Italy
A. Esposito, A. Gallo, C. Vaccarezza
INFN/LNF, Frascati (Roma), Italy
L. Faillace
RadiaBeam, Santa Monica, California, USA
G. Galzerano, E. Puppin, A. Tagliaferri
Politecnico/Milano, Milano, Italy
G. Mettivier, P. Russo
UniNa, Napoli, Italy
M. Placidi
LBNL, Berkeley, California, USA
G. Rossi
Università degli Studi di Milano, Milano, Italy
R.I. Saban
CERN, Geneva, Switzerland
A. Sarno
INFN-Napoli, Napoli, Italy
F. Stellato
INFN - Roma Tor Vergata, Roma, Italy
G. Turchetti
Bologna University, Bologna, Italy

MariX (Multidisciplinary advanced research infra-structure with X-rays) is a joint project of INFN and University of Milan, aiming at developing a twin X-ray Source of advanced characteristics for the future Sci-entific Campus of the University of Milan. Presently in its design study phase, it will be built in the post Expo area located in north-west Milan district. The first component of the X-source MariX is BriXS (Bright and compact X-ray Source), a Compton X-ray source based on superconducting cavities technology for the electron beam with energy recirculation and on a laser system in Fabry-Pérot cavity at a repetition rate of 100 MHz, producing 20-180 keV radiation for medical applications. The BriXS accelerator is also serving as injector of a 3.8 GeV superconductive linac, driving a X-ray FEL at 1 MHz, for providing coherent, moderate flux radiation at 0.3-10 KeV at 1 MHz. Scientific case, layout and typical parameters of MariX will be discussed.

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THPMF076

New Simulation Programs for Partially Stripped Ions - Laser Light Collisions

photon, laser, electron, factory

4249

C. Curatolo, L. Serafini
Istituto Nazionale di Fisica Nucleare, Milano, Italy
M.W. Krasny
LPNHE, Paris, France
W. Placzek
Marian Smoluchowski Institute of Physics, Jagiellonian University, Kraków, Poland

We present for the first time two new indipendent Monte Carlo codes for simulating the collisions of Partially Stripped Ions with Laser light. Such collisions if realised at LHC could drive a high intensity gamma source and are the back-bone of the recent Gamma Factory proposal. The implementation aspects will be discussed and the simulation results will be compared.

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THPMF082

Suppression of Microbunching Instability Using a Quadrupole Inserted Chicane in Free-Electron-Laser Linacs

bunching, linac, electron, laser

4267

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.

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THPMF084

Numerical Shot Noise Modeling and Particle Migration Scheme

micro-particles, bunching, radiation, electron

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.

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THPMF086

Reliability Improvement on Wiggler Period Averaging Approximation

wiggler, simulation, laser, plasma

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.

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THPMK016

Simulation Study of the NSRRC High Brightness Linac System and Free Electron Laser

linac, undulator, simulation, electron

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.

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THPMK026

Mobile Free-Electron Laser for Remote Atmospheric Survey

laser, electron, survey, free-electron-laser

4351

S. Johnson, G.A. Krafft, B. Terzić
ODU, Norfolk, Virginia, USA
G.A. Krafft
JLab, Newport News, Virginia, USA

Funding: This paper is authored by Jefferson Science Associates, LLC under U.S. DOE Contract No. DE-AC05- 06OR23177. E.J. was supported by the Virginia Space Grant Consortium, grant number 16-589.
Reliable atmospheric surveys for carbon distributions will be essential to building an understanding of the Earth's carbon cycle and the role it plays in climate change. One of the core needs of NASA 's Active Sensing of CO2 Over Nights, Days and Seasons (ASCENDS) Mission is to advance the range and precision of current remote atmospheric survey techniques. The feasibility of using accelerator-based sources of infrared light to improve current airborne lidar systems has been explored. A literary review has been conducted to asses the needs of ASCENDS versus the current capabilities of modern atmospheric survey technology, and the parameters of a free electron laser (FEL) source were calculated for a lidar system that will meet these needs. By using the "Next Linear Collider" from the Stanford Linear Accelerator Center (SLAC), a mobile FEL-based lidar may be constructed for airborne surveillance. The calculated energy of the lidar pulse is 0.1 joule: this output is a two orders of magnitude gain over current lidar systems, so in principle, the mobile FEL will exceed the needs of ASCENDS. Further research will be required to asses other challenges to mobilizing the FEL technology.

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THPMK028

Inverse Free Electron Laser Separatrix Crossing for Energy Gain and Stability

laser, undulator, electron, free-electron-laser

4354

N.S. Sudar, P. Musumeci
UCLA, Los Angeles, USA
D. Garzella
CEA, Gif-sur-Yvette, France

The laser wakefield accelerator (LWFA) has been proposed as a driver for next generation compact light sources. However, the beams produced by LWFA's typically exhibit correlated energy spread and energy jitter too large to drive the Free Electron Laser instability. We present here a novel scheme whereby using a highly non-linear strongly tapered undulator interaction directly after the LWFA we are able to trap and accelerate a large fraction of charge in the moving Inverse Free Electron Laser ponderomotive bucket. The final correlated energy spread and output energy are determined by the final bucket height and central energy of the ponderomotive bucket which are both determined by the stagnant undulator parameters, resulting in a significant decrease in the normalized energy spread (< 1%) and output energy jitter (< 1%). This interaction is treated both analytically and numerically.

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THPMK031

Elliptically Polarizing Undulator Design for PAL-XFEL

undulator, controls, operation, electron

4362

S.J. Lee, J.H. Han, D.E. Kim
PAL, Pohang, Kyungbuk, Republic of Korea

Funding: This research was supported by Basic Science Research Program through the National Research Foundation of Korea (NRF) funded by the Ministry of Science and ICT (2017R1C1B1012852).
Elliptically polarizing undulator (EPU) is under consideration as after-burner for the PAL-XFEL soft X-ray beamline to control the FEL polarization. In the soft X-ray line, seven planar undulators with a 35 mm period and 5 m length are in operation. To provide a polarization control of the FEL in the 1 to 3 nm wavelength, we compare the two types of EPUs, APPLE-II, and APPLE-X. The K value ranges for various operation modes are numerically studied for two undulator periods, 35 and 40 mm, of these EPU types.

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THPMK032

RADFET Installation at PAL-XFEL Undulator

undulator, radiation, controls, operation

4366

J.H. Han, Y.G. Jung, D.E. Kim, S.J. Lee, G. Mun
PAL, Pohang, Kyungbuk, Republic of Korea

Two undulator beamlines, one hard X-ray and one soft X-ray, are in operation at PAL-XFEL. Radiation produced during the FEL operation may impair the magnetic property of the undulator magnets and affect the FEL performance. Accumulated radiation at the undulator sections is being measured by using optically stimulated luminescent dosimeters (OSLDs) once per few months. Over 10 Gy gamma ray was detected at some locations at both undulator beamlines. However, in the measurement using the OSLDs we do not have information on which accelerator operation modes produce such high level of radiation on the undulators. To measure accumulated radiation in real time, we installed radiation-sensing field-effect transistors (RADFETs). We report the characteristics of the RADFET sensors and the installation at the PAL-XFEL undulator beamlines.

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THPMK033

PAL-XFEL Linac RF System Status

klystron, controls, operation, electron

4369

H.-S. Lee, Heo, J.Y. Heo, J.H. Hong, H.-S. Kang, K.H. Kim, S.H. Kim, D.H. Na, S.S. Park, Y.J. Park
PAL, Pohang, Kyungbuk, Republic of Korea

Funding: Ministry of Science and ICT
The PAL-XFEL Linear Accelerator began user support in March 2017 after one year of RF conditioning in 2016. The energy jitter was 0.013% when operating the H-X linear accelerator with 46 modulators, Klystron, LLRF, SSA and vacuum system at 6.838 GeV energy during user support period. So far, we have replaced four klystrons and 10 thyratron switches. We also measured the influence of temperature changes of RF components according to repetition rates of the machine. We will report on the measurement results of this operating experience and performance.

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THPMK034

Study on Effect of Phase Shifter on FEL Intensity at PAL-XFEL

undulator, electron, radiation, simulation

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.

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THPMK042

Two and Multiple Bunches at LCLS

laser, undulator, diagnostics, photon

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.

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THPMK043

Timing Stability at LCLS

timing, cavity, laser, linac

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.

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THPMK051

Theoretical Formulation of Improved SASE FEL Based on Slippage Enhancement Scheme

electron, undulator, radiation, laser

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)

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THPMK052

Numerical Simulation of Phase-Shift Method for Fel Power Enhancement in PAL-XFEL

undulator, electron, radiation, synchrotron

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)

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THPMK053

Simulation for LCLS-II Hard X-ray Self Seeding Scheme

undulator, photon, simulation, electron

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.

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THPMK054

Analysis of 1D FEL Sideband Instability with Inclusion of Energy Detune and Space Charge

space-charge, electron, undulator, laser

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)

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THPMK055

Self Seeding Scheme for LCLS-II-HE

emittance, electron, undulator, simulation

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.

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THPMK056

Effect of Transverse Radiation Defocusing in Post-Saturation Regime of High-Gain X-Ray Free-Electron Laser

electron, radiation, undulator, 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.

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THPMK060

Start-to-End Simulations of the CLARA FEL Test Facility

simulation, electron, undulator, laser

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.

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THPMK061

Isolated Few-Cycle Pulse Generation in X-Ray Free-Electron Lasers

electron, bunching, laser, free-electron-laser

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.

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THPMK064

RF System for SXFEL: C-band, X-band and S-band

linac, klystron, operation, LLRF

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.

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THPMK068

High degree circular polarization at x-ray self-seeding FELs with crossed-planar undulators

undulator, polarization, laser, electron

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.

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THPMK069

Design of the Beam Switchyard of a Soft X-ray FEL User Facility in Shanghai

linac, undulator, dipole, kicker

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.

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THPMK070

Optimization for the Two-Stage Hard X-Ray Self-Seeding Scheme the SCLF

undulator, radiation, electron, simulation

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.

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THPMK072

X-Band RF System as Linearizer for SXFEL

laser, electron, free-electron-laser, cavity

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.

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THPMK073

Multi FEL Lines with Compact Undulator Layout

undulator, electron, photon, laser

4470

D. Wang
SINAP, Shanghai, People's Republic of China

Today the high repetition rate X-ray Free Electron Lasers based on superconducting radiofrequency technologies have come to their age. Such kind of facilities are able to serve many FEL photon beamlines simultaneously with each of which have large flexibilities in selecting wavelength, intensity, polarization, coherence and other properties through independent tuning of the undulator magnets. In reality the space needed to accommodate many undulator lines could be a limiting factor of user capacity, especially for the high rep rate XFELs that tend to utilize the underground tunnel to host long superconducting accelerator machines. In this paper we present a concept of compact undulator layout for more FEL lines in the precious tunnel spaces or similar environment. Shanghai Coherent Light Facility(SCLF) is a high repe-tition rate X-ray Free Electron Lasers installed in under-ground tunnels with an overall length of more than 3 km. The concept described in this paper could be applied to the SCLF or similar FEL facilities. The design and R&D progress will be presented.

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THPMK076

Longitudinal Shaping for Beam-Driven Plasma Wakefield Accelerators

electron, linac, plasma, simulation

4477

Z. Wang, K.Q. Zhang, Z.T. Zhao
SINAP, Shanghai, People's Republic of China
S. Huang, W. Lu
TUB, Beijing, People's Republic of China

The generation of high quality driven electron beam (high peak current and small beam size) is quite important for the beam-driven plasma accelerator. Besides, a linearly ramped, more exactly, the triangular current distribution is more suitable. In this paper, by adjusting the phase and the amplitude of the harmonic linearizer, the linear ramped current distribution electron beam is generated by the FEL linac. The CSR introduced emittance growth and the jitters of the electron are researched. The electron beam generated by the ramped driven beam in the plasma is researched as well.

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THPMK077

The Preliminary Experiment Studies for Soft X-Ray Self-Seeding System Design of SCLF Facility

photon, experiment, simulation, electron

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.

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THPMK078

Corrugated Structure as a Linearizer in High Repetition Rate X-Ray Free Electron Laser Source

electron, linac, laser, simulation

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.

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THPMK106

Architectural Considerations for Recirculated and Energy-Recovered Hard XFEL Drivers

linac, recirculation, SRF, operation

4560

D. Douglas, S.V. Benson, T. Powers, Y. Roblin, T. Satogata, C. Tennant
JLab, Newport News, Virginia, USA
D. Angal-Kalinin, N. Thompson, A.E. Wheelhouse, P.H. Williams
STFC/DL/ASTeC, Daresbury, Warrington, Cheshire, United Kingdom
T.K. Charles
CERN, Geneva, Switzerland
R.C. York
FRIB, East Lansing, Michigan, USA

Funding: Authored by Jefferson Science Associates, LLC under U.S. DOE Contract No. DE-AC05-06OR23177.
A confluence of events motivates discussion of design options for hard XFEL driver accelerators. Firstly, multiple superconducting radio-frequency (SRF) driven systems are now online (European XFEL), in construction (LCLS-II), or in design (MARIE); these provide increasing evidence of the transformational potential they offer for fundamental science with its concomitant benefits. Secondly, operation of 12 GeV CEBAF* validates use of recirculation in high energy SRF linacs. Thirdly, advances in the analysis and control of effects such as coherent synchrotron radiation (CSR) and the microbunching instability (uBI) have been recently achieved. Collectively, these developments offer insights providing extended facility science reach, reduced costs, multiplicity (i.e., support of numerous FELs operating over a range of wavelengths), and enhanced scalability and upgradability (to higher powers and energies). We will discuss the relationship amongst the various threads, and indicate how they inform design choices for the system architecture of an option for the UK-XFEL** - that of a staged multi-user X-ray FEL and nuclear physics facility based on a multi-pass recirculating SRF CW linac.
*M. Spata, "12 GeV CEBAF Initial Operations and Challenges", these proceedings.
**P. Williams et al., Proc. FLS2018, Shanghai, China (March 2018).

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THPMK112

An Updated Description of the FEL Simulation Code Puffin

undulator, electron, radiation, distributed

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)

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THPMK124

The Radiation Source for a Pre-Bunched THz Free Electron Laser

radiation, electron, undulator, 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.

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THPMK126

Numerical Method for Longitudinal Dynamics of a Terahertz Cherenkov Free Electron Laser Driven by a Mev Picosecond Electron Beam

electron, radiation, wakefield, GUI

4614

W.W. Li, Z.G. He, Q.K. Jia, S.M. Jiang, 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: Natural Science Foundation of China (11705198, 11775216) China Postdoctoral Science Foundation (2017M622023) Fundamental Research Funds for the Central Universities (WK2310000061)
Corrugated or dielectric structures have been widely used for producing electron bunch train or THz radiation source. Recently, a novel scheme of sub-terahertz free electron laser (FEL) from a metallic pipe with corrugated walls driven by a non-ultra-relativistic (<10 MeV) picosecond electron beam was proposed and analyzed using the Vlasov-Maxwell equations. In this paper, we use the dielectric loaded waveguide instead, and a numerical method for the longitudinal beam dynamics and electromagnetics of the FEL interaction is presented.

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THPMK138

Power Enhancement of Free-Electron Lasers Oscillators With the Natural Gradient of a Planar Undulators

undulator, simulation, electron, radiation

4632

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.

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THPML033

Towards a Free Electron Laser Using Laser Plasma Acceleration

electron, laser, plasma, free-electron-laser

4723

A. Loulergue, T. André, I.A. Andriyash, C. Benabderrahmane, P. Berteaud, F. Blache, C. Bourassin-Bouchet, F. Bouvet, F. Briquez, L. Chapuis, M.-E. Couprie, D. Dennetière, Y. Dietrich, J.P. Duval, M. El Ajjouri, T.K. El Ajjouri, A. Ghaith, C. Herbeaux, N. Hubert, M. Khojoyan, C.A. Kitegi, M. Labat, N. Leclercq, A. Lestrade, O. Marcouillé, F. Marteau, P. N'gotta, D. Oumbarek, F. Polack, P. Rommeluère, M. Sebdaoui, K.T. Tavakoli, M. Valléau, J. Vétéran, C. de Oliveira
SOLEIL, Gif-sur-Yvette, France
S. Bielawski, C. Evain, E. Roussel, C. Szwaj
PhLAM/CERLA, Villeneuve d'Ascq, France
S. Corde, J. Gautier, J.-P. Goddet, G. Lambert, B. Mahieu, V. Malka, J.P. Rousseau, S. Sebban, K. Ta Phuoc, A. Tafzi, C. Thaury
LOA, Palaiseau, France
O. S. Kononenko
DESY, Hamburg, Germany
S. Smartzev
Weizmann Institute of Science, Physics, Rehovot, Israel

Since the laser invention, the advent of X-ray Free Electron Lasers (FEL) half a century later, opens new areas for matter investigation. In parallel, the spectacular development of laser plasma acceleration (LPA) with several GeV beam acceleration in an extremely short distance appears very promising. As a first step, the qualification of the LPA with a FEL application sets a first challenge. Still, energy spread and beam divergence do not meet the state-of-the-art performance of the conventional accelerators and have to be manipulated to fulfill the FEL requirement. We report here on the undulator spontaneous emission measured after a transport manipulation electron beam line, using variable permanent magnet quadrupoles of variable strength for emittance handing and a demixing chicane equipped with a slit for the energy spread. Strategies of control electron beam position and dispersion have been elaborated. The measured undulator radiation provides an insight on the electron beam properties.

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THPML061

X-Band Low Q Cavity Beam Position Monitor Study

cavity, simulation, electron, GUI

4777

S.S. Cao
SINAP, Shanghai, People's Republic of China
Y.B. Leng, R.X. Yuan
SSRF, Shanghai, People's Republic of China

The high repetition-rate and high peak brilliance of X-ray free-electron laser (XFEL) allow studying many scientific experiments that have not been feasible. To realize such high performance, a sub-micron beam transverse position measurement is required. The cavity-type beam position monitor (CBPM), as a non-destructive diagnostics tool with high potential in resolution performance, has been applied in different free electron laser facilities (FELs). In this research, an X-band high bandwidth CBPM has been studied and used for pre-research on bunch-by-bunch diagnostic for the pulsed FEL with high repetition-rate. Its bandwidth reaches 300 MHz. Design considerations and simulation results of the CBPM have been discussed and presented in this paper.

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THPML062

A Beam Based Method to Optimize the SBPM System

experiment, electron, quadrupole, site

4780

J. Chen
SINAP, Shanghai, People's Republic of China
L.W. Lai, Y.B. Leng, T. Wu, R.X. Yuan
SSRF, Shanghai, People's Republic of China

For the electron accelerator, it is hoped that the trajec-tory of the beam can pass through the magnetic center of the quadrupole to minimize the orbital motion caused by the instability of the power supply. The relative deviation between the magnetic center of quadrupole and the elec-tric center of adjacent BPM is measured by electron beam usually in various accelerator facilities. But for the stripline BPM (SBPM) system, in order to achieve the best performance, the beam trajectory should also need to pass through the electrical center of the SBPM system. In this paper, a beam based method to optimize the SBPM system was proposed, the intensity of the magnet power was scanned to change the beam position in two-dimension and combine the change trend of the sum signal of adjacent SBPM to find out the relative deviation of BPM electric center and mechanical center. Relevant beam experiment work on the Shanghai Soft X-ray free electron laser (SXFEL) and the benefit of this method will be addressed as well.

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THPML065

Preliminary Results of the Bunch Arrival-Time Monitor at SXFEL

electron, laser, pick-up, cavity

4787

J.G. Wang, B. Liu
SINAP, Shanghai, People's Republic of China

Based on an electro-optical intensity modulation detection scheme, a Bunch Arrival-time Monitor (BAM) is under study at Shanghai soft X-ray Free Electron Laser (SXFEL) to meet the high-resolution requirements of the measurement of bunch arrival time. The first BAM is installed and is being tested at the SXFEL upstream of the first short undulator (modulator) near the seed laser injection point. In this paper, we present the basic working principle, the design of the BAM system and report the preliminary test results.

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THPML067

SXFEL Linac BPM System Development and Performance Evaluation

linac, experiment, status, electron

4794

F.Z. Chen, T. Wu
SSRF, Shanghai, People's Republic of China
J. Chen, L.W. Lai, Y.B. Leng, L.Y. Yu, R.X. Yuan
SINAP, Shanghai, People's Republic of China

Shanghai Soft X-ray Free Electron Laser (SXFEL) is a test facility to study key technologies and new FEL physics. In order to deliver high quality electron beams to the undulator section, a high resolution (better than 10 microns with 200pC beam) Linac beam position monitor system has been developed. The system consists of stripline pickup and custom designed DBPM processor. The hardware and software architecture will be introduced in this paper. The online performance evaluation results will be presented as well.

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THPML071

Upgrade of Digital BPM Processor at DCLS and SXFEL

cavity, software, EPICS, FPGA

4807

L.W. Lai, F.Z. Chen, Y.B. Leng, T. Wu, Y.B. Yan
SSRF, Shanghai, People's Republic of China
J. Chen
SINAP, Shanghai, People's Republic of China

A digital BPM processor has been developed at 2016 in SINAP for DCLS and SXFEL, which are FEL facilities built in China. The stripline BPM and cavity BPM processors share the same hardware platform and firmware, but the processing algorithms implemented in EPICS IOC on the ARM CPU are different. The capability of the ARM limits the processing speed to 10 bunches per second. Now the bunch rate of DCLS and SXFEL are going to increase from 10Hz to 50Hz. To meet the higher processing speed requirements, the processor firmware and software are upgraded in 2017. All BPM signal processing algorithms are implemented in FPGA, and EPICS IOC reads results only. After the upgrade, the processing speed reach 120 bunches per second. And this is also a good preparation for future Shanghai Hard-X ray FEL, which bunch rate is about 1MHz.

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THPML109

Control System Design for Front End Devices of IRFEL

controls, power-supply, EPICS, interface

4920

S. Xu, G. Liu, Y. Song, X.K. Sun
USTC/NSRL, Hefei, Anhui, People's Republic of China

An Infrared Free Electron Laser Light (IRFEL) is being constructed at National Synchrotron Radiation Laboratory. IRFEL consists of e-gun, accelerating tube, microwave, klystron, power supply, vacuum, resonator, undulator, beam diagnosis, cooling water and other devices. The development of the control system for the front end devices of IRFEL is based on EPICS. This paper will introduce the hardware system design, Input Output Controller application, Operation Interface, data archiving and retrieval.

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THPML115

Introduction of the Laser Intensity Measurement System for the FELiChEM

laser, detector, electron, electronics

4936

F.L. Gao, L.T. Huang, P. Lu, B.G. Sun, J.G. Wang, F.F. Wu, Y.L. Yang, T.Y. Zhou
USTC/NSRL, Hefei, Anhui, People's Republic of China

The FELiChEM is a new infrared free electron laser (IR-FEL) facility, which is being built in the National Synchrotron Radiation Laboratory (NSRL) in Heifei, China. The facility will provide continuously tunable pulsed laser radiation covering the mid-infrared (MIR) wavelength range from 2.5 to 50μm and the far-infrared (FIR) range from 40 to 200μm. The output macro pulsed laser width is 5-10μs and pulsed laser power is 2-10kW. In order to evaluate pulsed laser saturation time and FEL optical cavity losses, the rise time and fall time of macro pulsed laser need to be measured. Laser intensity measurement system for the FELiChEM is being designed. This system is composed of optical system, pyroelectric detector and electronics. Each module will be described in detail in this paper. The laser intensity measurement system was tested under offline and online conditions. The results showed that pulsed laser of 10μs width can be measured and the design requirement can be met with this system.

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THPML127

Alignment and Installation for the FELiChEM project

alignment, laser, network, controls

4977

W. Wang, Zhang, H.T. H.T, X.Y. He, D.R. Xu
USTC/NSRL, Hefei, Anhui, People's Republic of China

Funding: Work supported by National Natural Science Foundation of China (11705199) and China Postdoctoral Science Foundation (2017M622024)
FELiChEM is a new experimental facility under construction at the University of Science and Technology of China. There are more than one hundred important devices to construct it, which core device is two free electron laser oscillators generating middle-infrared and far-infrared laser and covering the spectral range of 25-200μm. The optical cavity is an important component of oscillator which very sensitive to misalignment errors of the mirror, due to its near-concentric and symmetric structure. High precision alignment and installation is necessary to ensure the smooth implementation of the FELiChEM project. Laser tracker and Level are used to install this devices according to the alignment control network. An efficient and high-precision alignment method based on autocollimator and photoelectric auto-collimator is used to align optical cavity of oscillator. This methods is proven to be effective and meet the tolerances by multiple means.

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