WEP —  Wednesday Poster Session   (28-Aug-19   14:15—15:45)
Paper Title Page
WEP003 Balanced Optical-Microwave Phase Detector for 800-nm Pulsed Lasers with Sub-Femtosecond Resolution 322
 
  • K. Şafak, A. Berlin, E. Cano Vargas, H.P.H. Cheng, A. Dai, J. Derksen, M. Neuhaus, P. Schiepel
    Cycle GmbH, Hamburg, Germany
  • F.X. Kärtner
    Deutsches Elektronen Synchrotron (DESY) and Center for Free Electron Science (CFEL), Hamburg, Germany
 
  Novel light-matter interaction experiments conducted in free-electron lasers, ultrafast electron diffraction instruments and extreme light infrastructures require synchronous operation of microwave sources with femtosecond pulsed lasers [1]. In particular, Ti:sapphire lasers have become the most common near-infrared light source used in these facilities due to their wide-range tunability and their ability to generate ultrashort pulses at around 800-nm optical wavelength [2]. Therefore, a highly sensitive optical-to-microwave phase detector operating at 800 nm is an indispensable tool to synchronize these ubiquitous lasers to the microwave clocks of these facilities. Electro-optic sampling is one approach that has proven to be the most precise in extracting the relative phase noise between microwaves and optical pulse trains. However, their implementation at 800-nm wavelength has been so far limited [3]. Here, we show a balanced optical-microwave phase detector designed for 800-nm operation based on electro-optic sampling. The detector has a timing resolution of 0.01 fs RMS for offset frequencies above 100 Hz and a total noise floor of less than 10 fs RMS integrated from 1 Hz to 1 MHz.
[1] M. Xin, K. Shafak and F. X. Kärtner, Optica, vol. 5, no. 12, pp. 1564-1578, 2018.
[2] H. Yang et al., Scientific Reports, vol. 7, no. 39966, 2017.
[3] M. Titberidze, DESY-THESIS-2017-040, 2017.
 
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-FEL2019-WEP003  
About • paper received ※ 20 August 2019       paper accepted ※ 27 August 2019       issue date ※ 05 November 2019  
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WEP004 Timing Stability Comparison Study of RF Synthesis Techniques 325
 
  • E. Cano Vargas, F.X. Kärtner
    Deutsches Elektronen Synchrotron (DESY) and Center for Free Electron Science (CFEL), Hamburg, Germany
  • A. Berlin, H.P.H. Cheng, A. Dai, J. Derksen, P. Schiepel, K. Şafak
    Cycle GmbH, Hamburg, Germany
 
  Funding: Deutsches Elektronen-Synchrotron (DESY); Cycle GmbH.
High-precision and low-noise timing transfer from a master clock to different end stations of a free-electron laser (FEL) is an essential task.[1] Timing precisions ranging from few tens of femtoseconds to sub-femtoseconds are required for seeded FELs and attosecond science centers. Mode-locked lasers referenced to RF standards are commonly used as master oscillators, due to their superior stability and timing precision, depicting timing jitter in the attosecond range.[2] In this matter, one of the biggest challenges is to transfer the timing stability of mode-locked lasers to RF sources. Here, we compare and contrast two of the most common techniques used for laser-to-RF synthesis in FEL facilities: (i) RF signal extraction from the optical pulse train using photodiodes, and (ii) VCO-to-laser synchronization. Test setups are built to measure both the absolute phase noise of the generated RF signal and the relative timing jitter with respect to the mode-locked laser. Short-term timing jitter values varying between 10 and 100 fs are achieved for different test setups, while long term timing drift ranging to some hundreds of fs due to environmental influence are observed.
[1] M. Xin, K. Shafak and F.X. Kärtner, Optica, vol. 5, no. 12, pp. 1564-1578, 2018.
[2] J. Kim, F.X. Kärtner, Opt. Lett., vol. 32, pp. 3519-3521, 2007.
 
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-FEL2019-WEP004  
About • paper received ※ 20 August 2019       paper accepted ※ 27 August 2019       issue date ※ 05 November 2019  
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WEP006 A PolariX TDS for the FLASH2 Beamline 328
 
  • F. Christie, J. Rönsch-Schulenburg, M. Vogt
    DESY, Hamburg, Germany
 
  Transverse Deflecting RF-Structures (TDS) are successfully used for longitudinal diagnostic purposes at many Free-Electron Lasers (FEL) (LCLS, FLASH, EU-XFEL, FERMI). Moreover, by installing a TDS downstream of the FEL undulators and placing the measurement screen in a dispersive section, the temporal photon pulse structure can be estimated, as was demonstrated at LCLS and sFLASH. Here we describe the installation of a variable polarization X-band structure (PolariX TDS [1]) downstream of the FLASH2 undulators. The installation of such a TDS enables longitudinal phase space measurements and photon pulse reconstructions, as well as slice emittance measurements in both planes using the same cavity due to the unique variable polarization of the PolariX TDS.
[1] P. Craievich et al., "Status of the PolariX-TDS Project", in Proc. IPAC’18, Vancouver, Canada (2018)
 
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-FEL2019-WEP006  
About • paper received ※ 20 August 2019       paper accepted ※ 27 August 2019       issue date ※ 05 November 2019  
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WEP007 Usage of the MicroTCA.4 Electronics Platform for Femtosecond Synchronization Systems 332
 
  • M. Felber, E.P. Felber, M. Fenner, T. Kozak, T. Lamb, J. Müller, K.P. Przygoda, H. Schlarb, S. Schulz, C. Sydlo, M. Titberidze, F. Zummack
    DESY, Hamburg, Germany
 
  At the European XFEL and FLASH at DESY optical synchronization systems are installed providing sub-10 femtosecond electron bunch arrival time stability and laser oscillator synchronization to carry out time-resolved pump-probe experiments with high precision. The synchronization system supplies critical RF stations with short- and long-term phase-stable reference signals for precise RF field detection and control while bunch arrival times are processed in beam-based feedbacks to further time-stabilize the FEL pulses. Experimental lasers are tightly locked to the optical reference using balanced optical cross-correlation. In this paper, we describe the electronic hardware for supervision and real-time control of the optical synchronization system. It comprises various MicroTCA.4 modules including fast digitizers, FPGA processor boards, and drivers for piezos and stepper-motors. Advantages of the system are the high-level of integration, state-of-the-art performance, flexibility, and remote maintainability.  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-FEL2019-WEP007  
About • paper received ※ 20 August 2019       paper accepted ※ 26 August 2019       issue date ※ 05 November 2019  
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WEP008 Multi-Beamline Operation at the European XFEL 335
 
  • L. Fröhlich, A. Aghababyan, V. Balandin, B. Beutner, F. Brinker, W. Decking, N. Golubeva, O. Hensler, Y. Janik, R. Kammering, H. Kay, T. Limberg, S. Liu, D. Nölle, F. Obier, M. Omet, M. Scholz, T. Wamsat, T. Wilksen, J. Wortmann
    DESY, Hamburg, Germany
 
  The European XFEL uses a unique beam distribution scheme to direct electron bunches to its three undulator lines. The accelerator delivers up to 600 microsecond long bunch trains, out of which parts or individual bunches can be selected for photon production in any of the FELs. This contribution gives a brief overview of the kicker-septum scheme facilitating this and highlights how even complex bunch patterns can easily be configured via the timing system.  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-FEL2019-WEP008  
About • paper received ※ 19 August 2019       paper accepted ※ 29 August 2019       issue date ※ 05 November 2019  
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WEP009 Long Term Stability and Slow Feedback Performance at the European XFEL 339
 
  • R. Kammering
    DESY, Hamburg, Germany
 
  The European XFEL is now routinely running in user operation since more than two years. Up to 8 longitudinal and 9 transversal slow feedback loops are routinely used to keep the accelerators chosen operation conditions. First tests of comparing the machine ’free-floating’ state versus fully fixing all relevant monitoring signals have been carried out and show interesting results. Here we will review the feedback systems in terms of software architecture and conceptual layout but also in respect to feedback and FEL performance.  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-FEL2019-WEP009  
About • paper received ※ 20 August 2019       paper accepted ※ 29 August 2019       issue date ※ 05 November 2019  
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WEP010 Femtosecond Laser-to-RF Synchronization and RF Reference Distribution at the European XFEL 343
 
  • T. Lamb, M. Felber, T. Kozak, J. Müller, H. Schlarb, S. Schulz, C. Sydlo, M. Titberidze, F. Zummack
    DESY, Hamburg, Germany
 
  At the European XFEL, optical pulses from a mode-locked laser are distributed in an optical fiber network providing femtosecond stability throughout the accelerator facility. Due to the large number of RF reference clients and because of the expected higher reliability, the 1.3 GHz RF reference signals are distributed by a conventional coaxial RF distribution system. However, the provided ultra-low phase noise 1.3 GHz RF reference signals may drift over time. To remove these drifts, an optical reference module (REFM-OPT) has been developed to detect and correct environmentally induced phase errors of the RF reference. It uses a femtosecond long-term stable laser-to-RF phase detector, based on an integrated Mach-Zehnder amplitude modulator (MZM), to measure and resynchronize the RF phase with respect to the laser pulses from the optical synchronization system with high accuracy. Currently nine REFM-OPTs are permanently operated at the European XFEL, delivering femtosecond stable RF reference signals for critical accelerating field control stations. The operation experience will be reported together with a detailed evaluation of the REFM-OPT performance.  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-FEL2019-WEP010  
About • paper received ※ 20 August 2019       paper accepted ※ 28 August 2019       issue date ※ 05 November 2019  
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WEP011 Longitudinal Intra-Train Beam-Based Feedback at FLASH 346
 
  • S. Pfeiffer, Ł. Butkowski, M.K. Czwalinna, B. Dursun, C. Gerth, B. Lautenschlagerpresenter, H. Schlarb, Ch. Schmidt
    DESY, Hamburg, Germany
 
  The longitudinal intra-train beam-based feedback has been recommissioned after major upgrades on the synchronization system of the FLASH facility. Those upgrades include: new bunch arrival time monitors (BAMs), the optical synchronization system accommodating the latest European XFEL design based on PM fibers, and installation of a small broadband normal conducting RF cavity. The cavity is located prior to the first bunch compressor at FLASH and allows energy modulation bunch-by-bunch (1 us spacing) on the per mille range. Through the energy dependent path length of the succeeding magnetic chicane the cavity is used for ultimate bunch arrival time corrections. Recently the RF cavity operated 1 kW pulsed solid-state amplifier was successfully commissioned. First tests have been carried out incorporating the fast cavity as actuator together with SRF stations for larger corrections in our intra-train beam-based feedback pushing now arrival time stabilities towards 5 fs (rms). The latest results and observed residual instabilities are presented.  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-FEL2019-WEP011  
About • paper received ※ 20 August 2019       paper accepted ※ 17 September 2019       issue date ※ 05 November 2019  
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WEP012 THz Spectroscopy with MHz Repetition Rates for Bunch Profile Reconstructions at European XFEL 350
 
  • N.M. Lockmann, C. Gerth, B. Schmidt, S. Wesch
    DESY, Hamburg, Germany
 
  The European X-ray Free-Electron Laser generates most powerful and brilliant X-ray laser pulses. Exact knowledge about the longitudinal electron bunch profile is crucial for the operation of the linear accelerator as well as for photon science experiments. The only longitudinal diagnostic downstream of the main linac is based on spectroscopy of diffraction radiation (DR). The spectral intensity of the DR in the THz and infrared regime is monitored by a four-staged grating spectrometer and allows non-invasive bunch length characterization based on form factor measurements in the range 0.7 - 60 THz. As the readout and signal shaping electronics of the spectrometer allow MHz readout rates, the longitudinal bunch profile of all bunches inside the bunch train can be characterized non-invasively and simultaneously to FEL operation. In this paper, form factor measurements along the bunch train will be described and presented as well as the resulting reconstructed current profiles.  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-FEL2019-WEP012  
About • paper received ※ 20 August 2019       paper accepted ※ 29 August 2019       issue date ※ 05 November 2019  
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WEP013 Fast Kicker System for European XFEL Beam Distribution 353
 
  • F. Obier, W. Decking, M. Hüning, J. Wortmann
    DESY, Hamburg, Germany
 
  A special feature of the European XFEL X-ray laser is the possibility to distribute the electron bunches of one beam pulse to different free-electron laser (FEL) beam-lines. This is achieved through a combination of kickers and a Lambertson DC septum. The integration of a beam abort dump allows a flexible selection of the bunch pattern at the FEL experiment, while the superconducting linear accelerator operates with constant beam loading. The driver linac of the FEL can deliver up to 600 µs long bunch trains with a repetition rate of 10 Hz and a maximum energy of 17.5 GeV. The FEL process poses very strict requirements on the stability of the beam position and hence on all upstream magnets. It was therefore decided to split the beam distribution system into two kicker systems, long pulse kickers with very stable amplitude (flat-top) and relatively slow pulses and fast stripline kickers with moderate stability but very fast pulses. This contribution gives a brief overview of the fast kicker system.  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-FEL2019-WEP013  
About • paper received ※ 20 August 2019       paper accepted ※ 27 August 2019       issue date ※ 05 November 2019  
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WEP014 Long Pulse Kicker for European XFEL Beam Distribution 357
 
  • F. Obier, W. Decking, M. Hüning, J. Wortmann
    DESY, Hamburg, Germany
 
  A special feature of the European XFEL X-ray laser is the possibility to distribute the electron bunches of one beam pulse to different free-electron laser (FEL) beam-lines. This is achieved through a combination of kickers and a Lambertson DC septum. The integration of a beam abort dump allows a flexible selection of the bunch pattern at the FEL experiment, while the superconducting linear accelerator operates with constant beam loading. The driver linac of the FEL can deliver up to 600 µs long bunch trains with a repetition rate of 10 Hz and a maximum energy of 17.5 GeV. The FEL process poses very strict requirements on the stability of the beam position and hence on all upstream magnets. It was therefore decided to split the beam distribution system into two kicker systems, long pulse kickers with very stable amplitude (flat-top) and relatively slow pulses and fast stripline kickers with moderate stability but very fast pulses. This contribution gives a brief overview of the long pulse kicker system.  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-FEL2019-WEP014  
About • paper received ※ 20 August 2019       paper accepted ※ 27 August 2019       issue date ※ 05 November 2019  
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WEP015 Electro-Optical Bunch Length Detection at the European XFEL 360
 
  • B. Steffen, M.K. Czwalinna, C. Gerth
    DESY, Hamburg, Germany
  • S. Bielawski, C. Evain, E. Roussel, C. Szwaj
    PhLAM/CERCLA, Villeneuve d’Ascq Cedex, France
 
  The electro-optical bunch length detection system based on electro-optic spectral decoding has been installed and is being commissioned at the European XFEL. The system is capable of recording individual longitudinal bunch profiles with sub-picosecond resolution at a bunch repetition rate of 1.13MHz . Bunch lengths and arrival times of entire bunch trains with single-bunch resolution have been measured as well as jitter and drifts for consecutive bunch trains. In addition, we are testing a second electro-optical detection strategy, the so-called photonic time-stretching, which consists of imprinting the electric field of the bunch onto a chirped laser pulse, and then "stretching" the output pulse by optical means. As a result, we obtain is a slowed down "optical replica" of the bunch shape, which can be recorded using a photodiode and GHz-range acquisition. These tests are performed in parallel with the existing spectral decoding technique based on a spectrometer in order to allow a comparative study. In this paper, we present first results for both detection strategies from electron bunches after the second bunch compressor of the European XFEL.  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-FEL2019-WEP015  
About • paper received ※ 24 August 2019       paper accepted ※ 28 August 2019       issue date ※ 05 November 2019  
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WEP016 Precise Laser-to-RF Synchronization of Photocathode Lasers 364
 
  • M. Titberidze, M. Felber, T. Kozak, T. Lamb, J. Müller, H. Schlarb, S. Schulz, C. Sydlo, F. Zummack
    DESY, Hamburg, Germany
 
  RF photo-injectors are used in various large, mid and small-scale accelerator facilities such as X-ray Free Electron Lasers (XFELs), external injection-based laser-driven plasma accelerators (LPAs) and ultrafast electron diffraction (UED) sources. Many of these facilities require a high precision synchronization of the photo-injector laser system, either because of beam dynamics reasons or the photo-injector directly impacting pump-probe experiments carried out to study physical processes on femtosecond timescales. It is thus crucial to achieve synchronization in the order of 10 fs rms or below between the photocathode laser and the RF source driving the RF gun. In this paper, we present the laser-to-RF synchronization setup employed to lock a commercial near-infrared (NIR) photocathode laser oscillator to a 2.998 GHz RF source. Together with the first results achieving ~ 10 fs rms timing jitter in the measurement bandwidth from 10 Hz up to 1 MHz, we describe an advanced synchronization setup as a future upgrade, promising even lower timing jitter and most importantly long-term timing drift stability.  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-FEL2019-WEP016  
About • paper received ※ 20 August 2019       paper accepted ※ 27 August 2019       issue date ※ 05 November 2019  
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WEP019 Concept of a Novel High-Bandwidth Arrival Time Monitor for Very Low Charges as a Part of the All-Optical Synchronization Systems at XFEL and FLASH 368
 
  • A. Penirschke
    THM, Friedberg, Germany
  • W. Ackermann
    TEMF, TU Darmstadt, Darmstadt, Germany
  • M.K. Czwalinna, H. Schlarb
    DESY, Hamburg, Germany
 
  Funding: This work is supported by the German Federal Ministry of Education and Research (BMBF) under contract no. 05K19RO1.
Numerous advanced applications of X-ray free-electron lasers require pulse durations and time resolutions in the order of only a few femtoseconds or better. The generation of these pulses to be used in time-resolved experiments require synchronization techniques that can simultaneously lock all necessary components to a precision in the range of 1 fs only. To improve the experimental conditions at existing facilities and enable future development of seeded FELs, a new all-optical synchronization system at FLASH and XFEL was implemented, which is based on pulsed optical signals rather than electronic RF signals. In collaboration with DESY, Hamburg the all-optical synchronization system is used to ensure a timing stability on the 10 fs scale at XFEL. For a future ultra-low charge operation mode down to 1 pC at XFEL an overall synchronization of (5+1)fs r.m.s. or better is necessary. This contribution presents a new concept for a ultra-wideband pick-up structure for beampipe diameters down to 10 mm for frequencies up to 100 GHz or higher and at the same time providing sufficient output signal for the attached EOMs.
 
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-FEL2019-WEP019  
About • paper received ※ 23 August 2019       paper accepted ※ 28 August 2019       issue date ※ 05 November 2019  
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WEP024 1.3 GHz Solid State Power Amplifier for the Buncher in CTFEL Facility 371
 
  • T.H. He, C.L. Lao, P. Lipresenter, X. Luo, L.J. Shan, K. Zhou
    CAEP/IAE, Mianyang, Sichuan, People’s Republic of China
 
  The THz Free Electron Laser facility (CAEP THz FEL, CTFEL) of the China Academy of Engineering Physics uses high quality electron beams to generate high average power terahertz radiations. A 1.3 GHz RF buncher is used in front of the superconducting linear accelerator of the CTFEL facility to improve the electron beams quality. The RF buncher is driven by a solid state power amplifier (SSPA), and the SSPA is feedback controlled by a low level RF (LLRF) control system to ensure the high stability of the amplitude and phase of the bunching field in the buncher cavity. The SSPA operates at 1.3 GHz and outputs 0 to 5 kW of continuous wave power. This paper mainly introduces the principle and composition of the SSPA, and presents some experiments on the RF buncher driven by the SSPA.  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-FEL2019-WEP024  
About • paper received ※ 15 August 2019       paper accepted ※ 27 August 2019       issue date ※ 05 November 2019  
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WEP026 Preliminary Geometry Optimization of a 3.5-Cell SRF Gun Cavity at ELBE Based on Beam Dynamics 374
 
  • K. Zhou, P. Li
    CAEP/IAE, Mianyang, Sichuan, People’s Republic of China
  • A. Arnold, S. Ma, J. Schaber, J. Teichert, R. Xiangpresenter
    HZDR, Dresden, Germany
 
  At present, ELBE radiation source at HZDR is optimizing the SRF cavity for the next generation ELBE SRF GUN. This paper presents a preliminary study on the geometry optimization of a 3.5-cell SRF gun cavity based on beam dynamics. By changing the lengths of the half cell and the first TESLA like cell, two new cavity models with higher electric field in the half cell are built and their RF fields are compared with SRF GUN I and SRF GUN II. Through the scanning of the RF phases and the electric fields, the simulation results indicate that new models have smaller transverse emittance at relatively lower electric field gradients and better performance on longitudinal emittance than SRF GUN I and SRF GUN II.  
poster icon Poster WEP026 [1.345 MB]  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-FEL2019-WEP026  
About • paper received ※ 19 August 2019       paper accepted ※ 29 August 2019       issue date ※ 05 November 2019  
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WEP027 A Fast and Accurate Method to Shim Undulator Using Multi-Objective GA 378
 
  • L.G. Yan, L.J. Chen, D.R. Deng, P. Lipresenter
    CAEP/IAE, Mianyang, Sichuan, People’s Republic of China
 
  Funding: National Natural Science Foundation of China under grant of 11505174, 11505173 and 11605190
GA (Genetic Algorithm) is one of the most excellent methods to search the optimal solution for a problem, which has been applied to solve various problems. It is hard to estimate shim applied on raw undulator precisely. There are many methods have been developed to solve the problem. In this proceeding, we proposed a fast and accurate method to conclude the shim using multi-objective GA. A multi-objective objective function was set, and multi-objective optimization was also implemented. The evolution time is reduced by setting optimal evolution parameters. To demonstrate the method, we also finished some test on a prototype undulator U38. As a result, it can be achieved only by shimming three times that all the parameters of trajectory center deviation, peak-to-peak error and phase error satisfied the requirements.
 
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-FEL2019-WEP027  
About • paper received ※ 20 August 2019       paper accepted ※ 27 August 2019       issue date ※ 05 November 2019  
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WEP030 All-Fiber Photonic, Ultralow-Noise, Robust Optical and Microwave Signal Generators for FELs and UED 382
 
  • J. Kim, I.J. Jeon, D. Kim, D. Kwonpresenter
    KAIST, Daejeon, Republic of Korea
 
  Funding: National Research Foundation of Korea (2018R1A2B3001793) and Korea Atomic Energy Research Institute
Optical timing and synchronization is becoming a more important and essential element for ultrafast X-ray and electron science. As a result, compact, ultralow-noise, mechanically robust and long-term stable optical and microwave signal generators are highly desirable for future XFELs and UEDs. Here we show that the combination of mode-locked fiber laser and fiber delay-based stabilization method enables the generation of ultralow-noise optical and microwave signals. We show that all-PM fiber lasers can provide excellent mechanical robustness: stable laser operation over >1 hour is maintained even in continuous 1.5 g vibrations [1]. Using a compactly packaged fiber delay as the timing reference, we could stabilize the repetition-rate phase noise of mode-locked lasers down to -100 dBc/Hz and -160 dBc/Hz at 1 Hz and 10 kHz offset frequency, respectively, at 1 GHz carrier, which corresponds to only 1.4 fs rms absolute timing jitter [1 Hz - 100 kHz] [2]. With DDS-based electronics, low-noise and agile microwave frequency synthesizer was also realized [3]. This new class of photonic signal generator will be suitable for master oscillators in various accelerator-based light sources.
[1] D. Kim et al., Opt. Lett. 44, 1068 (2019)
[2] D. Kwon et al., Opt. Lett. 42, 5186 (2017)
[3] J. Wei et al., Photon. Res. 6, 12 (2018)
 
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-FEL2019-WEP030  
About • paper received ※ 05 September 2019       paper accepted ※ 22 October 2019       issue date ※ 05 November 2019  
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WEP031 Timing Synchronization Activities for Drift-Free Operation of Ultrafast Electron Diffraction System at KAERI 385
 
  • J. Shin, J. Kim
    KAIST, Daejeon, Republic of Korea
  • I.H. Baek, Y.U. Jeong, H.W. Kim, K. Oang, S. Park
    KAERI, Daejon, Republic of Korea
 
  Funding: This work is funded by KAERI (Grant number: 525350-19)
Precise timing synchronization of an ultrafast electron diffraction facility is essential requirement for femtosecond resolution structure analysis. Recent studies of THz-based electron deflectors have enabled the timing drift measurement between ultrafast electrons and an optical pump beam with few femtosecond resolution [1]. In this work, we will introduce timing synchronization activities to suppress the drift of an electron beam. As timing drift of the electron beam originates from every sub-element, each timing drift contribution from RF transfer, RF-to-optical synchronization, and optical amplification is measured. Timing drift of RF transfer through coaxial cable, which exposed to temperature fluctuation, is actively stabilized from 2 ps to 50 fs by active feedback loop. Further additive drift from RF-to-optical synchronization is maintained below 100 fs. Also optical drift due to the regenerative amplifier, measured by optical correlator, is maintained below 20 fs over an hour. This work allows ultrafast electron diffraction system to operate with less drift correction procedure and increased user availability.
[1] H. Yang et al., "10-fs-level synchronization of photocathode laser with RF-oscillator for ultrafast electron and X-ray sources", Sci. Rep. 7, 39966 (2017).
 
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-FEL2019-WEP031  
About • paper received ※ 24 August 2019       paper accepted ※ 25 August 2019       issue date ※ 05 November 2019  
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WEP034 Characterization of FEL Spectra Using Specific Figures of Merit 388
 
  • M.A. Pop, F. Curbis
    MAX IV Laboratory, Lund University, Lund, Sweden
  • E. Allaria
    Elettra-Sincrotrone Trieste S.C.p.A., Basovizza, Italy
  • F. Curbis
    SLF, Lund, Sweden
 
  By analyzing the spectral content of FEL electron radiation, we can gain new information about the properties of the electron bunch and on the FEL process itself. In this work, we present a peak detection algorithm and its capabilities in characterizing the spectra of seeded FEL.
This work is done in collaboration with FERMI Elettra-Sincrotrone Trieste, Area Science Park, Trieste, Italy
 
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-FEL2019-WEP034  
About • paper received ※ 20 August 2019       paper accepted ※ 25 August 2019       issue date ※ 05 November 2019  
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WEP035 NIR Spectrometer for Bunch-Resolved, Non-Destructive Studies of Microbunching at European XFEL 392
 
  • S. Fahlström, M. Hamberg
    Uppsala University, Uppsala, Sweden
  • C. Gerth, N.M. Lockmann, B. Steffen
    DESY, Hamburg, Germany
 
  At the European X-ray Free Electron Laser high brilliance femtosecond FEL radiation pulses are generated for user experiments. For this to be achieved electron bunches must be reliably produced within very tight tolerances. In order to investigate the presence of micro-bunching, i.e. charge density variation along the electron bunch with features in the micron range, a prism-based NIR spectrometer with an InGaAs sensor, sensitive in the wavelength range 900 nm to 1700 nm was installed. The spectrometer utilizes diffraction radiation (DR) generated at electron beam energies of up to 17.5 GeV. The MHz repetition rate needed for bunch resolved measurements is made possible by the KALYPSO line detector system, providing a read-out rate of up to 2.7 MHz. We present the first findings from commissioning of the NIR spectrometer, and measurements on the impact of the laser heater system for various bunch compression settings, in terms of amplitude and bunch-to-bunch variance of the NIR spectra as well as FEL pulse energy.  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-FEL2019-WEP035  
About • paper received ※ 20 August 2019       paper accepted ※ 29 August 2019       issue date ※ 05 November 2019  
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WEP036 The PolariX-TDS Project: Bead-Pull Measurements and High-Power Test on the Prototype 396
 
  • P. Craievich, M. Bopp, H.-H. Braun, A. Citterio, R. Ganter, T. Kleeb, F. Marcellini, M. Pedrozzi, E. Prat, S. Reiche
    PSI, Villigen PSI, Switzerland
  • R.W. Aßmann, F. Christie, R.T.P. D’Arcy, U. Dorda, M. Foese, P. Gonzalez Caminal, M. Hoffmann, M. Hüning, R. Jonas, O. Krebs, S. Lederer, V. Libov, B. Marchetti, D. Marx, J. Osterhoff, M. Reukauff, H. Schlarb, S. Schreiber, G. Tews, M. Vogt, A. Wagner
    DESY, Hamburg, Germany
  • N. Catalán Lasheras, A. Grudiev, G. McMonagle, W.L. Millar, S. Pitman, K.T. Szypula, W. Wuensch, V. del Pozo Romano
    CERN, Meyrin, Switzerland
  • W.L. Millar
    Cockcroft Institute, Warrington, Cheshire, United Kingdom
 
  A collaboration between DESY, PSI and CERN has been established to develop and build an advanced modular X- band transverse deflection structure (TDS) system with the new feature of providing variable polarization of the deflecting force. The prototype of the novel X-band TDS, the Polarizable X-band (PolariX) TDS, was fabricated at PSI following the high-precision tuning-free production process developed for the C-band Linac of the SwissFEL project. Bead-pull RF measurements were also performed at PSI to verify, in particular, that the polarization of the dipole fields does not have any rotation along the structure. The high-power test was performed at CERN and now the TDS is at DESY and has been installed in FLASHForward, where the first streaking experience with beam will be accomplished. We summarize in this paper the status of the project, the results of the bead-pull measurements and the high power test.  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-FEL2019-WEP036  
About • paper received ※ 21 August 2019       paper accepted ※ 26 August 2019       issue date ※ 05 November 2019  
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WEP037 RF Jitter and Electron Beam Stability in the SwissFEL Linac 400
 
  • Z.G. Geng, J. Alex, V.R. Arsov, P. Craievichpresenter, C.H. Gough, R. Kalt, T. Lippuner, F. Löhl, M. Pedrozzi, E. Prat, S. Reiche
    PSI, Villigen PSI, Switzerland
 
  The X-ray FEL machine SwissFEL at the Paul Scherrer Institut in Switzerland is commissioned and transiting to user operation smoothly. FEL operation requires stringent requirements for the beam stability at the linac output, such as the electron bunch arrival time, peak current and energy. Among other things, a highly stable RF system is required to guarantee the beam stability. The SwissFEL RF system is designed based on the state-of-the-art technologies that have allowed achieving excellent RF stability. The propagation of RF amplitude and phase jitter to the electron beam are analyzed theoretically and compared with the measurements performed at SwissFEL.  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-FEL2019-WEP037  
About • paper received ※ 20 August 2019       paper accepted ※ 27 August 2019       issue date ※ 05 November 2019  
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WEP038 Commissioning and Stability Studies of the SwissFEL Bunch-Separation System 404
 
  • M. Paraliev, S. Dordevic, R. Ganter, C.H. Gough, N. Hiller, R.A. Krempaská, D. Voulot
    PSI, Villigen PSI, Switzerland
 
  SwissFEL is a linear electron accelerator based, X-ray Free Electron Laser at the Paul Scherrer Institute, Switzerland. It is a user oriented facility capable of producing short, high brightness X-ray pulses covering the spectral range from 1 to 50 Å. SwissFEL is designed to run in two electron bunch mode in order to serve simultaneously two experimental beamline stations (hard and soft X-ray one) at its full repetition rate. Two closely spaced (28 ns) electron bunches are accelerated in one RF macro pulse up to 3 GeV. A high stability resonant kicker system and a Lambertson septum magnet are used to separate the bunches and to send them to their respective beamlines. With the advancement of the construction of the second beamline (Athos) the bunch-separation system was successfully commissioned. In order to confirm that the beam separation process is fully transparent a stability study of the electron beam and the free electron laser in the main beamline (Aramis) was done.  
poster icon Poster WEP038 [0.945 MB]  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-FEL2019-WEP038  
About • paper received ※ 19 August 2019       paper accepted ※ 25 August 2019       issue date ※ 05 November 2019  
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WEP041 Feasibility of Single-Shot Microbunching Diagnostics for a Pre-Bunched Beam at 266 nm 408
 
  • A.H. Lumpkin
    AAI/ANL, Lemont, Illinois, USA
  • D.W. Rule
    Private Address, Silver Spring, USA
 
  Funding: Work supported by U.S. Department of Energy, Office of Science, under Contract No. DE-AC02-06CH11357.
Co-propagating a relativistic electron beam and a high-power laser pulse through a short undulator (modulator) provides an energy modulation which can be converted to a periodic longitudinal density modulation (or microbunching) via the R56 term of a chicane. Such pre-bunching of a beam at the resonant wavelength and the harmonics of a subsequent free-electron laser (FEL) amplifier seeds the process and results in improved gain. We describe potential characterizations of the resulting microbunched electron beams using coherent optical transition radiation (COTR) imaging techniques for transverse size (50 micron), divergence (sub-mrad), trajectory angle (0.1 mrad), spectrum (few nm), and pulse length (sub-ps). The transverse spatial alignment is provided with near-field imaging and the angular alignment is done with far-field imaging and two-foil COTR interferometry (COTRI). Analytical model results for a 266-nm wavelength COTRI case with a 10% microbunching fraction will be presented. COTR gains of 7 million were calculated for an initial charge of 300 pC which enables splitting the optical signal for single-shot measurements of all the cited parameters.
 
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-FEL2019-WEP041  
About • paper received ※ 20 August 2019       paper accepted ※ 29 August 2019       issue date ※ 05 November 2019  
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WEP042 Observations of Short-Range Wakefield Effects in TESLA-Type Superconducting RF Cavities 412
 
  • A.H. Lumpkin, D.R. Edstrom, J. Ruan, R.M. Thurman-Keup
    Fermilab, Batavia, Illinois, USA
 
  Funding: This manuscript has been authored by Fermi Research Alliance, LLC under Contract No. DE-AC02-07CH11359 with the U.S. Department of Energy, Office of Science, Office of High Energy Physics.
The accelerators for high power X-ray free-electron laser (FEL) facilities such as the European XFEL and planned LCLS-II X-ray FEL are employing TESLA-type SCRF cavities. Beam propagation off axis in these cavities can result in both short-range and long-range transverse wakefields which can lead to emittance dilution within the micropulses and macropulses, respectively. The Fermilab Accelerator Science and Technology (FAST) facility has a unique configuration of a photocathode RF gun beam injecting two TESLA-type single cavities (CC1 and CC2) in series prior to the cryomodule. To investigate short-range wakefield effects, we used a vertical corrector between these two cavities to steer the beam off axis at an angle into CC2. A Hamamatsu synchroscan streak camera viewing a downstream OTR screen provided an image of y-t effects within the micropulses with resolutions of ~10-micron spatial and 2-ps temporal. At 500 pC/b, 50 b, and 4 mrad off-axis steering, we observed an ~100-micron head-tail centroid shift in the streak camera image. This centroid shift is consistent with a calculated short-range wakefield effect. Additional results for kick-angle compensation will be presented.
 
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-FEL2019-WEP042  
About • paper received ※ 20 August 2019       paper accepted ※ 28 August 2019       issue date ※ 05 November 2019  
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WEP043 Multi-Energy Operation Analysis in a Superconducting Linac Based on off-Frequency Detune Method 416
 
  • Z. Zhang, C. Adolphsen, Y. Dingpresenter, T.O. Raubenheimer
    SLAC, Menlo Park, California, USA
 
  The free-electron laser facilities driven by a superconducting radio-frequency (SRF) linac provide high-repetition-rate electron beam, which makes it feasible to feed multiple undulator lines at the same time. In this paper, we study a method of controlling the beam energy of multiple electron bunches by off-frequency detuning of the SRF linac. Based on the theoretical analysis, we present the optimal solutions of the method and the strategy to allocate linac energy for each possible off-frequency detune. The initial acceleration phases before detuning of the SRF linac can be optimized to reduce the necessary SRF linac energy overhead. We adopt the LCLS-II-HE configuration as an example to discuss possible schemes for two undulator lines.  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-FEL2019-WEP043  
About • paper received ※ 20 August 2019       paper accepted ※ 27 August 2019       issue date ※ 05 November 2019  
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WEP045 Status of the Klystrons for the European XFEL after Commissioning and First User Operation Phase 420
 
  • V. Vogel (Fogel), M. Bousonville, A. Cherepenko, S. Choroba, H.-J. Eckoldt, T. Grevsmühl, V.V. Katalev, K. Machau, P. Morozov, B. Yildirim
    DESY, Hamburg, Germany
 
  At present 26 RF stations for the European XFEL are in operation. Each of the RF stations consists of a HV modulator located on the DESY campus, up to 1600 m long 10 kV HV cables that connect the modulators and the HV pulse transformers located in the underground tunnel, the horizontal multi-beam klystron (MBK), and an air filled waveguide distribution system (WG) between the klystron and the cavities input couplers. The klystrons can produce RF power up to 10 MW, 1.5 ms RF pulse length and 10 Hz repetition rate. Two RF stations of the injector have already achieved about 30,000 hours of operation, RF stations of the XFEL bunch compressor area have operated up to 20,000 hours and the klystrons in the XFEL main linac already have about 18,000 hours of operation. To increase the lifetime of the klystrons we are using a fast protection system (KLM) that is in routine operation since 2018 in addition to the common interlock system. In this article we will give a summary of the present klystrons operation status including the number of HV and RF arcs in the klystrons and in the WG system and operation statistics for the high power RF part of machine.  
poster icon Poster WEP045 [0.757 MB]  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-FEL2019-WEP045  
About • paper received ※ 20 August 2019       paper accepted ※ 12 September 2019       issue date ※ 05 November 2019  
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WEP046 The European XFEL Photocathode Laser 423
 
  • L. Winkelmann, A. Choudhuripresenter, U. Grosse-Wortmann, I. Hartl, C. Li, C. Mohr, J. Müller, F. Peters, S. Pfeiffer, S.H. Salman
    DESY, Hamburg, Germany
 
  We present the Yb:fiber, Nd:YVO4 laser used to generate electrons from the RF photocathode gun at the European XFEL. The laser provides deep UV output pulses in 600 µs bursts with variable internal repetition rate (564 kHz to 4.5 MHz). Due to its robust architecture (mode-locked and synchronized fiber oscillator, Yb:fiber amplifiers and Nd:YVO4 gain blocks), the laser has operated with >99% uptime since January 2017. Using this laser, the XFEL reported energies of 17.5 GeV in July 2018, and simultaneous multi-mJ lasing in its three SASE beamlines. The laser offers two parallel outputs (1064 nm) with single pulse energies of >100 µJ and 11 ps width (FWHM). One output is converted to deep UV with efficiencies > 25%, and the second is used as a laser heater to reduce microbunching instabilities to increase SASE efficiency. Several state-of-art laser controls were implemented, including feed-forward algorithm to flatten electron charge along the bunch, active beam stabilization with < ±10 µm jitter at the photocathode, state machines for hands-off end-user operation, and temporal pulse synchronization and drift compensation to the timing jigger of the electron bunches to less than 45 fs.  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-FEL2019-WEP046  
About • paper received ※ 23 August 2019       paper accepted ※ 29 August 2019       issue date ※ 05 November 2019  
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WEP047 Update on the Photocathode Lifetime at FLASH and European XFEL 427
 
  • S. Lederer, F. Brinker, S. Schreiber
    DESY, Hamburg, Germany
  • L. Monaco, D. Sertore
    INFN/LASA, Segrate (MI), Italy
 
  The photoinjectors of FLASH and the European XFEL at DESY (Hamburg, Germany) are operated by laser driven RF-guns. In both facilities Cs2Te photocathodes are successfully used. In this paper we give an update on the lifetime, quantum efficiency (QE) and dark current of the photocathodes used over the last years. At FLASH cathode #73.3 was operated for a record lifetime of 1413 days and was replaced December 2018 by cathode #105.2. At the European XFEL cathode #680.1 is in operation since December 2015, for 1356 days up to now.  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-FEL2019-WEP047  
About • paper received ※ 20 August 2019       paper accepted ※ 28 August 2019       issue date ※ 05 November 2019  
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WEP048 FLASH Photoinjector Laser Systems 430
 
  • S. Schreiber, C. Grün, K. Klose, J. Rönsch-Schulenburg, B. Steffen
    DESY, Hamburg, Germany
 
  The free-electron laser facility FLASH at DESY (Hamburg, Germany) operates two undulator beamlines simultaneously for FEL operation and a third for plasma acceleration experiments (FLASHForward). The L-band superconducting technology allows accelerating fields of up to 0.8 ms in length at a repetition rate of 10 Hz (burst mode). A fast kicker-septum system picks one part of the 1 MHz electron bunch train and kicks it to the second beamline such that two beamlines are operated simultaneously with the full repetition rate of 10 Hz. The photoinjector operates three laser systems. They have different pulse durations and transverse shapes and are chosen to serve best for the given user experiment in terms of electron bunch charge, bunch compression, and bunch pattern. It is also possible to operate the laser systems on the same beamline to provide specific double pulses for certain type of experiments.  
poster icon Poster WEP048 [2.642 MB]  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-FEL2019-WEP048  
About • paper received ※ 26 August 2019       paper accepted ※ 27 August 2019       issue date ※ 05 November 2019  
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WEP049 RF Power Waveguide Distribution for the RF Gun of the European XFEL at DESY 434
 
  • B. Yildirim, S. Choroba, V.V. Katalev, P. Morozov, Y. Nachtigal
    DESY, Hamburg, Germany
  • E.M. Apostolov
    Technical University of Sofia, Sofia, Bulgaria
 
  The first section of the European XFEL provides the 43 m long injector. The injector consists of a 1.3 GHz RF gun, a 1.3 GHz cryomodule, a 3.9 GHz cryomodule and an extensive diagnostic section. The RF gun operates with a maximum RF peak power up to 6.5 MW, 10 Hz repetition rate and up to 650 µs pulse length. The starting point in the 1.5 cell normal conducting L-Band cavity of the RF gun is a Cs2Te photocathode, which produces electron bunches, which are injected into the superconducting accelerating section of the European XFEL. The RF power is generated by a 10 MW multi beam klystron and distributed to the RF gun through a RF power waveguide distribution system. In order to enhance the reliability of the distribution system, the peak power is minimized in every section of the system by splitting the power in different branches. The RF power reaches its maximum just in front of the RF gun after combination of all branches. An additional air pressure system decreases the break down level in the waveguides of the distribution. We present the layout of the waveguide distribution system for the XFEL RF gun at DESY and report on first operation experience.  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-FEL2019-WEP049  
About • paper received ※ 19 August 2019       paper accepted ※ 27 August 2019       issue date ※ 05 November 2019  
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WEP050 Status of Chirped Pulse Laser Shaping for the PITZ Photoinjector 437
 
  • C. Koschitzki, Y. Chen, J.D. Good, M. Groß, M. Krasilnikov, G. Loisch, R. Niemczyk, F. Stephan
    DESY Zeuthen, Zeuthen, Germany
  • E. Khazanov, S. Mironov
    IAP/RAS, Nizhny Novgorod, Russia
  • T. Lang, L. Winkelmann
    DESY, Hamburg, Germany
 
  The beam emittance at FEL facilities like European XFEL and FLASH is dominated by the emittance sources in the electron injector. Shaping of the laser pulses that are employed to release electrons from the cathode of a photo injector, was shown in theory to allow improved beam emittance starting from the electron emission process. At the photo injector test facility at DESY in Zeuthen (PITZ) a laser system capable of controlling the temporal and spatial profile of laser pulses is being set up to demonstrate the predicted emittance reduction experimentally. The presentation will show its current capabilities to provide temporally and spatially shaped laser pulses from a pulse shaper operating at infrared (IR) wavelengths. Furthermore, results from a shape preserving conversion into fourth harmonic ultra-violet (UV), as needed for the photo emission process, will be presented.  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-FEL2019-WEP050  
About • paper received ※ 21 August 2019       paper accepted ※ 17 September 2019       issue date ※ 05 November 2019  
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WEP051 PITZ Experimental Optimization for the Aimed Cathode Gradient of a Superconducting CW RF Gun 440
 
  • M. Krasilnikov, P. Boonpornprasert, Y. Chen, G.Z. Georgiev, J.D. Good, M. Groß, P.W. Huang, I.I. Isaev, C. Koschitzki, S. Lal, X. Li, O. Lishilin, G. Loisch, D. Melkumyan, R. Niemczyk, A. Oppelt, H.J. Qian, H. Shaker, G. Shu, F. Stephan, G. Vashchenko
    DESY Zeuthen, Zeuthen, Germany
  • M. Dohlus, E. Vogel
    DESY, Hamburg, Germany
 
  A continuous wave (CW) mode operation of the European X-ray Free-Electron Laser (XFEL) is under considerations for a future upgrade. Therefore, a superconducting radio frequency (SRF) CW gun is under experimental development at DESY in Hamburg. Beam dynamics simulations for this setup have been done assuming 100 pC bunch charge and a maximum electric field at the photocathode of 40 MV/m. Experimental studies for these parameters using a normal conducting RF photogun have been performed at the Photo Injector Test facility at DESY in Zeuthen (PITZ). The beam transverse emittance was minimized by optimizing the main photo injector parameters in order to demonstrate the feasibility of generating electron beams with a beam quality required for successful CW operation of the European XFEL for conditions similar to the SRF gun setup.  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-FEL2019-WEP051  
About • paper received ※ 20 August 2019       paper accepted ※ 27 August 2019       issue date ※ 05 November 2019  
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WEP052 Simulation Studies on the Saturated Emission at PITZ 444
 
  • X. Li, P. Boonpornprasert, Y. Chen, J.D. Good, M. Groß, I.I. Isaev, C. Koschitzki, M. Krasilnikov, S. Lal, O. Lishilin, G. Loisch, D. Melkumyan, R. Niemczyk, A. Oppelt, H.J. Qian, H. Shaker, G. Shu, F. Stephan, G. Vashchenko
    DESY Zeuthen, Zeuthen, Germany
 
  In this paper we report our consideration and simulation on the space charge dominated emission in the L-band photocathode RF gun at the Photo Injector Test facility at DESY in Zeuthen (PITZ). It has been found that the emission curve, which relates the extracted and accelerated bunch charge after the gun to the laser energy, doesn’t agree very well with Astra simulations when the emission is nearly or fully saturated. Previous studies with a core-halo model for a better fit of the experimentally measured laser transverse profile as well as with an improved transient emission model have resulted in a better agreement between experimental data and simulation. A 3D FFT space charge solver including mirror charge and binned energy/momentum has been built, which also allows more emission mechanisms to be included in the future. In this paper, the energy spread during emission was preliminarily analyzed. Experimentally measured emission curves were compared with simulation, showing the effect of the inhomogeneity of the laser on the emission and beam parameters.  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-FEL2019-WEP052  
About • paper received ※ 20 August 2019       paper accepted ※ 27 August 2019       issue date ※ 05 November 2019  
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WEP053 Development of a Multialkali Antimonide Photocathode at INFN LASA 448
 
  • S.K. Mohanty
    DESY Zeuthen, Zeuthen, Germany
  • G. Guerini Rocco, C. Pagani
    Università degli Studi di Milano & INFN, Segrate, Italy
  • P. Michelato, L. Monaco, D. Sertore
    INFN/LASA, Segrate (MI), Italy
 
  Owing to their excellent properties including high quantum efficiency (QE), low emittance, good lifetime and fast response, alkali antimonides photocathodes has been considered as one of the eminent candidates for the electron source of energy recovery linacs (ERL) and free electron lasers (FEL). Nevertheless, their sensitivity to vacuum condition requires specific R&D before they can operate in a RF Gun. For this reason, we have started to develop specifically K-Cs-Sb based multialkali photocathodes at INFN LASA. The primary goal is to develop a stable and reproducible alkali antimonide films on INFN plugs and test them in the photoinjector test facility PITZ at DESY Zeuthen. In this report, we present and discuss about the results so far obtained on KCsSb material and the status of the new preparation system specifically designed for these sensitive materials.  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-FEL2019-WEP053  
About • paper received ※ 08 August 2019       paper accepted ※ 27 August 2019       issue date ※ 05 November 2019  
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WEP054 Beam Dynamics Optimization of a Normal-Conducting Gun Based CW Injector for the European XFEL 452
 
  • H. Shaker, S. Lal, H.J. Qian, G. Shu, F. Stephan
    DESY Zeuthen, Zeuthen, Germany
 
  The European XFEL is operating up to 17.5 GeV electron energy with maximum 0.65% duty cycle. There is a prospect for continuous wave and long pulse mode (CW/LP) operation of the European XFEL, which enables more flexible bunch pattern time structure for experiments, higher average brightness and better stability. Due to engineering limitations, the maximum electron beam energy in the CW/LP mode is about 8.6/12.8 GeV, which puts more pressure on the injector beam quality for lasing at the shortest wavelength. This paper optimizes the beam dynamics of an injector based on a normal-conducting VHF gun.  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-FEL2019-WEP054  
About • paper received ※ 20 August 2019       paper accepted ※ 26 August 2019       issue date ※ 05 November 2019  
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WEP055 Multiphysics Analysis of a CW VHF Gun for European XFEL 456
 
  • G. Shu, Y. Chen, S. Lal, H.J. Qian, H. Shaker, F. Stephan
    DESY Zeuthen, Zeuthen, Germany
 
  R&D for a possible future CW mode operation of European XFEL started after the successful commissioning of the pulse mode operation. For the CW electron source upgrade, a fully superconducting CW gun is under experimental development at DESY in Hamburg, and a normal conducting (NC) CW gun is under physics design at the Photo Injector Test facility at DESY in Zeuthen (PITZ) as a backup option. Based on the experience of the LBNL on a 187 MHz gun, the DESY 217 MHz gun increased the cathode gradient and RF power to 28 MV/m and 100 kW, respectively, to further improve the beam brightness. In this paper, the multiphysics analysis investigating the RF, thermal and mechanical properties of the 217 MHz NC CW gun are presented.  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-FEL2019-WEP055  
About • paper received ※ 20 August 2019       paper accepted ※ 28 August 2019       issue date ※ 05 November 2019  
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WEP056 Engineering Design of Low-Emittance DC-SRF Photocathode Injector 460
 
  • Y.Q. Liu, M. Chen, S. Huang, L. Lin, K.X. Liu, S.W. Quan, F. Wang, S. Zhao
    PKU, Beijing, People’s Republic of China
 
  An upgraded version of DC-SRF photocathode injector (DC-SRF-II) is under development at Peking University. The goal is to achieve an emittance below 0.5 mm-mrad at the bunch charge of 100 pC and repetition rate of 1 MHz. The engineering design of the DC-SRF-II photoinjector was accomplished in this May and the fabrication is ongoing now. This paper presents some details of the engineering design.  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-FEL2019-WEP056  
About • paper received ※ 19 August 2019       paper accepted ※ 26 August 2019       issue date ※ 05 November 2019  
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WEP057 Performance Optimization of Low-Emittance DC-SRF Injector Using Cs2Te Photocathode 463
 
  • S. Zhao
    Peking University, Beijing, People’s Republic of China
  • S. Huang, K.X. Liu, Y.Q. Liu, D.M. Ouyang
    PKU, Beijing, People’s Republic of China
 
  A low-emittance DC-SRF injector (DC-SRF-II) is under construction at Peking University, in the earlier design of which K2CsSb photocathode was chosen. Recently we changed the cathode to Cs2Te, which is more widely used nowadays, and carried out a detailed performance optimization. In this paper, we present our latest simulation results, which show that an emittance under 0.5 mm-mrad can be achieved at the bunch charge of 100 pC.  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-FEL2019-WEP057  
About • paper received ※ 14 August 2019       paper accepted ※ 27 August 2019       issue date ※ 05 November 2019  
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WEP058 Drive Laser Temporal Shaping Techniques for Shanghai Soft X-Ray Free Electron Laser 466
 
  • X.T. Wang, T. Lan, M. Zhang, W.Y. Zhang
    SINAP, Shanghai, People’s Republic of China
  • L. Feng, B. Liu
    SARI-CAS, Pudong, Shanghai, People’s Republic of China
  • C.L. Lipresenter
    Shanghai Advanced Research Institute, Pudong, Shanghai, People’s Republic of China
 
  The design of Shanghai soft X-ray free electron laser (SXFEL) is based on laser driven photocathode, which can provide emittance <2.0 mm’mrad with 500 pC charge. The temporal shape of drive laser has significant influence on the electron beam emittance and brightness. This paper presents the transport line of drive laser system and the temporal shaping techniques for SXFEL. This drive laser produces 8 picosecond 266nm ultraviolet pulses with repetition rate 10Hz. A transverse deflecting cavity was used for indirectly characterizing the laser pulse temporal structure. Here we present the drive laser system with its temporal shaping method, and measurement results.  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-FEL2019-WEP058  
About • paper received ※ 20 August 2019       paper accepted ※ 28 August 2019       issue date ※ 05 November 2019  
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WEP059 Characterizing a Coherent Electron Source Extracted From a Cold Atom Trap 469
 
  • H. Luo, P.X. Chu, J. Guo, T. Liu, Y.X. Xu, X. Zhao
    SWUST, Mianyang City, Sichuan Province, People’s Republic of China
  • X.H. Li, Q.H. Zhou
    Southwest University of Science and Technology, Mianyang, Sichuan, People’s Republic of China
  • K. Wang
    USTC, Hefei, Anhui, People’s Republic of China
 
  Funding: The National Natural Science Foundation of China under Grant No. 11875227.
In order to generate a fully coherent free electron laser (FEL) within a compact system, one approach is to interact a coherent electron bunch with a high power laser operating in the quantum FEL regime. The coherent electron source is obtained by ionizing the Rydberg atoms in a magneto-optical trap (MOT). The qualities of the electron source will have direct effects on the brightness, coherence, and line width of the free electron laser. A high quality ultra-cold electron source is obtained by carefully optimizing the extraction electrode structure, the acceleration and focusing system as well as the MOT. Through parameter optimization, a coherent electron source with a temperature lower than 10 K is obtained. Details of the optimization and the characteristics of the coherent electron source are reported in this paper.
 
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-FEL2019-WEP059  
About • paper received ※ 24 August 2019       paper accepted ※ 10 September 2019       issue date ※ 05 November 2019  
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WEP062 Test of Cs2Te Thickness on Cathode Performance at PITZ 473
 
  • P.W. Huang
    TUB, Beijing, People’s Republic of China
  • Y. Chen, M. Groß, I.I. Isaev, P. Kitisri, C. Koschitzki, M. Krasilnikov, S. Lal, X. Li, O. Lishilin, D. Melkumyan, R. Niemczyk, A. Oppelt, H.J. Qian, H. Shaker, G. Shu, F. Stephan, G. Vashchenko, T. Weilbach
    DESY Zeuthen, Zeuthen, Germany
  • A. Grigoryan
    CANDLE, Yerevan, Armenia
  • S. Lederer
    DESY, Hamburg, Germany
  • P. Michelato, L. Monaco, D. Sertore
    INFN/LASA, Segrate (MI), Italy
 
  Cesium telluride is a widely used cathode in photo injectors, and its performance is one of the keys for not only emittance but also reliable operation. Over the years lots of experiences with Cs2Te photocathodes produced with the same recipe and thickness were gained at the DESY photo injectors, but cathode performance dependence on the cathode layer thickness were not investigated. In this paper, we test fresh Cs2Te cathodes with different thickness at the Photo Injector Test Facility at DESY in Zeuthen (PITZ). The QE and thermal emittance of these cathodes inside the high gradient RF gun will be compared. Besides, the injector emittance under the operation conditions of the XFEL will also be measured with these cathodes.  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-FEL2019-WEP062  
About • paper received ※ 20 August 2019       paper accepted ※ 27 August 2019       issue date ※ 05 November 2019  
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WEP063 The Preliminary Study of a Pre-Bunched Terahertz Free Electron Laser by a Velocity Bunching Scheme 477
 
  • R. Huang, Q.K. Jia, H.T. Li, Z. Zhao
    USTC/NSRL, Hefei, Anhui, People’s Republic of China
 
  Funding: Work supported by the National Natural Science Foundation of China Grant Number 11805200
Terahertz (THz) radiation has broad applications in biological sciences, materials imaging and radar communications and so on. High-power, frequency-adjustable THz radiation sources are desired. An electron beam, generated in a photoinjector and bunched at terahertz (THz) frequency, will excite a coherent THz radiation when entering an undulator. The radiation power mainly depends on the particle number and the bunching factor of the electron beam, which is limited by the space charge effect among the microbunches and the total rf phase width the macrobunch occupied. Previously we have designed a pre-bunched THz free electron laser (FEL) with the radiation frequency covering 0.5-5 THz. While the radiation intensity for the lower frequency (below 1~THz) is not very high because of the large energy spread and the low bunching factor. We will report a THz FEL by a velocity bunching scheme, which could realize more highly bunched beam especially in the low THz frequency region. The physical design of the electron source is described in detail.
 
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-FEL2019-WEP063  
About • paper received ※ 19 August 2019       paper accepted ※ 28 August 2019       issue date ※ 05 November 2019  
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WEP064 Performance of S-Band Photocathode RF Gun With Coaxial Coupler 481
 
  • J.H. Hong, J.H. Han, C.-K. Min
    PAL, Pohang, Kyungbuk, Republic of Korea
 
  To improve the characteristics of electron beams, new S-band photocathode RF gun with a coaxial coupler has been developed and fabricated at the Pohang Accelerator Laboratory (PAL). This new RF gun is improved the field symmetry inside the cavity cell by applying the coaxial coupler, and the cooling performance by improving the cooling lines. The RF gun is installed in the injector test facility (ITF) for high power RF test. This paper reports the recent results on the RF conditioning process and the beam tests of the RF gun with high power RF at ITF. We present and discuss the measurement results of the basic beam parameters.  
poster icon Poster WEP064 [0.784 MB]  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-FEL2019-WEP064  
About • paper received ※ 24 August 2019       paper accepted ※ 26 August 2019       issue date ※ 05 November 2019  
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WEP067 Development and Commissioning of a Flip Coil System for Measuring Field Integrals 484
 
  • J.E. Baader
    UNICAMP, Campinas, São Paulo, Brazil
 
  Funding: CAPES grant numbers 88881.134183/2016-01; DOE contract DE-AC02-76SF00515 in support of the LCLS-II project; and FAEPEX-UNICAMP grant number 519.292/94550-19.
Many techniques for measuring magnetic fields are available for accelerator magnets. In general, methods based upon moving wires are suitable for characterizing field harmonics, and first and second field integrals. The flip coil moving wire technique stands out due to simplicity, speed, precision, and accuracy. We aimed to develop a reliable, fast and precise flip coil system capable of characterizing field integrals in the two transverse axes. The coil was a single turn loop made of insulated beryllium copper wire. The width of the loop was 5 mm. The approach of measuring second field integrals by changing the coil’s width at one of the ends was analyzed and included in the system. High-performance motorized stages performed angular and transverse positioning of the coil, while manual stages were used to stretch the wire, execute fine adjustments in its transverse position, and change coil’s geometry. Initial tests with the Earth’s field and also with a reference magnet of 126 Gauss-centimeter (G.cm) demonstrated that the system achieves repeatability of 0.2 G.cm for a 60-cm long coil. This work was carried out for the LCLS-II project at SLAC.
 
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-FEL2019-WEP067  
About • paper received ※ 08 August 2019       paper accepted ※ 26 August 2019       issue date ※ 05 November 2019  
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WEP070 Influence of Radiation Exposure on the FEL Performance at FLASH 488
 
  • B. Faatz, M. Tischer, P. Vaginpresenter
    DESY, Hamburg, Germany
 
  FLASH has been operated as user facility for about 14 years. In this time, the total charge accelerated and transported through the FLASH1 undulator is around 35 Coulomb. Based on detailed monitoring of the radiation loss and reference measurements on degradation of the magnetic field of the undulator, we have performed simulations to study the change in FEL performance and first comparison of the simulations with the changes we observe during operation.  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-FEL2019-WEP070  
About • paper received ※ 07 August 2019       paper accepted ※ 27 August 2019       issue date ※ 05 November 2019  
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WEP072 Expected Radiation Properties of the Harmonic Afterburner at FLASH2 492
 
  • M. Mehrjoo, B. Faatz, G. Paraskaki, M. Tischer, P. Vagin
    DESY, Hamburg, Germany
 
  We discuss the afterburner option to upgrade the FLASH2 undulator line, at the FLASH facility in the Hamburg area, for delivering short wavelengths down to approximately 1.5 nm with variable polarization. This relatively straightforward upgrade enables us the study of the scientific cases in L- absorption edges of rare earth metals. The proposed afterburner setting with an energy upgrade to 1.35 GeV would potentially cover many of the community’s requests for the short wavelengths radiation and circular polarization. We also study the influence of reverse tapering on the radiation output. This contribution presents a series of simulations for the afterburner scheme and some of the technical choices made for implementation.  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-FEL2019-WEP072  
About • paper received ※ 19 August 2019       paper accepted ※ 28 October 2019       issue date ※ 05 November 2019  
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WEP073 Experience With MCP-Based Photon Detector at FLASH2 495
 
  • S. Grunewald, E. Muller, E. Schneidmiller, K.I. Tiedtke, M.V. Yurkovpresenter
    DESY, Hamburg, Germany
  • O.I. Brovko, A.Yu. Grebentsov, E. Syresin
    JINR, Dubna, Moscow Region, Russia
 
  In this report we describe MCP-based radiation detector at FLASH2. Micro-channel plate (MCP) detects scattered radiation from a target (mesh). Use of different targets and geometrical positioning of the MCP plates provides control of photon flux on the detector. MCP detector covers the whole wavelength range of FLASH2 (from 2.x nm to 100 nm). Dynamic range spans from sub-nJ to mJ level (from spontaneous to saturation level). Relative accuracy of single-shot radiation pulse energy measurements in the exponential gain regime is about 1%. DAQ based software is under development which allows to perform cross-correlation of the SASE FEL performance with electron beam jitters. As a result, it is possible: (i) to organize efficient feedback for cancellation of machine jitters, and (ii) to use statistical techniques for characterization of SASE FEL radiation deriving such important quantities as gain curve (gain of the radiation pulse energy and its fluctuations along the undulator), radiation pulse duration, coherence time, and degree of transverse coherence. Relevant experimental results are presented in the paper.  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-FEL2019-WEP073  
About • paper received ※ 19 August 2019       paper accepted ※ 26 August 2019       issue date ※ 05 November 2019  
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WEP076 A Superconducting Undulator With Variable Polarization Direction for the European FEL 499
 
  • Y. Li
    EuXFEL, Hamburg, Germany
  • R. Rossmanith
    DESY, Hamburg, Germany
 
  In the SASE3 beam line at the European XFEL a planar undulator produces linearly polarized radiation. In order to obtain a circularly polarized radiation an afterburner will be installed to produce coherent radiation with variable polarization. Recently Argonne National Lab developed a super conductive undulator (called SCAPE) for a storage ring which allows to change polarization direction and field strength without moving mechanically the undulator parts. In this paper it is investigated if a similar device could be useful for an FEL. Such device is also a possible choice for the future undulator beam lines where circular and variable polarization are required.  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-FEL2019-WEP076  
About • paper received ※ 19 August 2019       paper accepted ※ 17 September 2019       issue date ※ 05 November 2019  
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WEP079 Effect of Heat Load on Cryo-Cooled Monochromators at the European X-Ray Free-Electron Laser: Simulations and First Experimental Observations 502
 
  • I. Petrov, U. Boesenberg, M. Dommach, J. Eidam, J. Hallmann, K. Kazarian, C. Kim, W. Lu, A. Madsen, J. Möller, M. Reiser, L. Samoylova, R. Shayduk, H. Sinn, V. Sleziona, A. Zozulya
    EuXFEL, Schenefeld, Germany
  • J.W.J. Anton, S.P. Kearney, D. Shu
    ANL, Lemont, Illinois, USA
  • X. Dong
    SINAP, Shanghai, People’s Republic of China
  • X. Dong
    SARI-CAS, Pudong, Shanghai, People’s Republic of China
 
  European XFEL (EuXFEL) generates high-intensity ultra-short pulses at MHz repetition rate. At hard X-ray instruments, cryo-cooled silicon monochromators are used to reduce pulse bandwidth. Here, first experimental observations during commissioning of a cryo-cooled monochromator at Materials Imaging and Dynamics (MID) instrument are presented and compared with heat flow simulations. A thermal relaxation time is estimated and compared with arrival time interval between pulses. This provides the repetition rate tolerable for stable operation of monochromator.  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-FEL2019-WEP079  
About • paper received ※ 19 August 2019       paper accepted ※ 25 August 2019       issue date ※ 05 November 2019  
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WEP080 ROSA: Reconstruction of Spectrogram Autocorrelation for Self-Amplified Spontaneous Emission Free-Electron Lasers 506
 
  • S. Serkez, G. Geloni, N. Gerasimova
    EuXFEL, Schenefeld, Germany
  • O. Gorobtsov
    Cornell University, Ithaca, New York, USA
  • B. Sobko
    LNU, Lviv, Ukraine
 
  X-ray Free Electron Lasers (FELs) have opened new avenues in photon science, providing coherent X-ray radiation pulses orders of magnitude brighter and shorter than previously possible. The emerging concept of "beam by design" in FEL accelerator physics aims for accurate manipulation of the electron beam to tailor spectral and temporal properties of radiation for specific experimental purposes, such as X-ray pump/X-ray probe and multiple wavelength experiments. A cost-efficient method to extract information on longitudinal Wigner distribution function of emitted FEL pulses is proposed. It requires only an ensemble of measured FEL spectra.  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-FEL2019-WEP080  
About • paper received ※ 20 August 2019       paper accepted ※ 26 August 2019       issue date ※ 05 November 2019  
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WEP081 Design and Development of High-Speed Data Acquisition System and Online Data Processing with a Heterogeneous FPGA/GPU Architecture 510
 
  • M. Bawatna, J.-C. Deinert, O. Knodel, S. Kovalev
    HZDR, Dresden, Germany
  • R.G. Spallek
    Technische Universität Dresden, Dresden, Germany
 
  The superradiant THz sources at TELBE facility is based on the new class of accelerator-driven terahertz (THz) radiation sources that provide high repetition rates up to 13 MHz, and flexibility of tuning the THz pulse form. The THz pulses are used for the excitation of materials of interest, about two orders of magnitude higher than state-of-the-art tabletop sources. Time-resolved experiments can be performed with a time resolution down to 30 femtoseconds (fs) using the novel pulse-resolved Data Acquisition (DAQ) system. However, the increasing demands in improving the flexibility, data throughput, and speed of the DAQ systems motivate the integration of reconfigurable processing units close to the new detectors to accelerate the processing of tens of GigaBytes of data per second. In this paper, we introduce our online ultrafast DAQ system that uses a GPU platform for real-time image processing, and a custom high-performance FPGA board for interfacing the image sensors and provide a continuous data transfer.  
poster icon Poster WEP081 [0.830 MB]  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-FEL2019-WEP081  
About • paper received ※ 18 August 2019       paper accepted ※ 25 August 2019       issue date ※ 05 November 2019  
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WEP085 Field Integral Measurements of DAVV Undulators and Future Measurement Plan 513
 
  • M. Gehlot, S.M. Khan, R. Khullar, G. Mishra
    Devi Ahilya University, Indore, India
  • J. Hussain
    Department of Applied Physics, UIT, Bhopal, India
  • F. Trillaud
    UNAM, México, D.F., Mexico
 
  Funding: This work is supported by SERB-DST grant EMR/2014/00120 and financial support from UGC [F.15-1/2014-15/PDFWM-2014-15-GE-MAD-26801(SA-II)], Delhi and DGAPA of UNAM, fund PAPIIT TA100617
The Insertion device development and Application (IddA) laboratory of Devi Ahilya University, Indore, India has ongoing activities on undulator design and development. In this paper, we analyze the field integral properties of the two DAVV undulator. The first is the IddA U20 prototype NdFeB-cobalt steel hybrid in house designed device of 20 mm period length with twenty five periods. The uniform gap variable hybrid undulator provides magnetic flux density (in rms) from 2400 G to 500 G in the 10 mm to 20 mm gap range. The second is the NdFeB based U50II undulator of 50 mm period length with 20 number of periods. Hall probe results are described. A short description of the measurement plan of the undulator on the pulsed wire bench and stretched wire bench is described.
 
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-FEL2019-WEP085  
About • paper received ※ 20 August 2019       paper accepted ※ 26 August 2019       issue date ※ 05 November 2019  
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WEP086 Capabilities of Terahertz Super-Radiance from Electron Bunches Moving in Micro-Undulators 517
 
  • N. Balal, V.L. Bratman, A. Friedman, Yu. Lurie
    Ariel University, Ariel, Israel
  • V.L. Bratman
    IAP/RAS, Nizhny Novgorod, Russia
 
  Funding: This work was supported by the Israeli Ministry of Science, Technology and Space and by the Russian Foundation for Basic Research, grant No. 16-02-00794.
An available frequency range of coherent radiation from ps bunches with high charge and moderate particle energy significantly enhances if one uses a micro-undulator with a high transverse field. Such an undulator can be implemented by redistributing a strong uniform magnetic field by a helical ferromagnetic or copper insertion. According to simulations and experiments with prototypes, a steel helix with a period of (8-10) mm and an inner diameter of (1.5-2) mm inserted in the 3T-field of solenoid can provide an undulator field with an amplitude of 0.6 T. Using a hybrid system with a permanently magnetized structure can increase this value up to 1.1 T. The necessary steel helices can be manufactured on the machine, assembled from steel wires, formed from powder, or 3D - printed. Simulations based on the WB3D code demonstrate that using such undulators with the length of (30-40) cm enable single-mode super-radiance from bunches with energy of 6 MeV, charge of 1 nC and duration of 2 ps moving in an over-sized waveguide in frequency range of 3-5 THz. The calculated efficiency of such process is (2-4)% that many times exceeds efficiency for short bunches of the same initial density.
 
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-FEL2019-WEP086  
About • paper received ※ 14 August 2019       paper accepted ※ 28 August 2019       issue date ※ 05 November 2019  
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WEP089 Pulse Energy Measurement at the SXFEL 521
 
  • Z.P. Liu, H.X. Deng, C. Feng, B. Liu, D. Wang, L.Y. Yu
    SINAP, Shanghai, People’s Republic of China
 
  The test facility is going to generate 8.8 nm FEL radiation using an 840 MeV electron linac passing through the two-stage cascaded HGHG-HGHG or EEHG-HGHG (high-gain harmonic generation, echo-enabled harmonic generation) scheme. Several methods have been developed to measure the power of pulse. The responsivity of silicon photodiode having no loss in the entrance window. Silicon photodiode reach saturates at the SXFEL. In this work, we simulated the attenuator transmittance for different thicknesses. We also show the preparations of the experiment results at the SXFEL .  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-FEL2019-WEP089  
About • paper received ※ 20 August 2019       paper accepted ※ 28 August 2019       issue date ※ 05 November 2019  
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WEP092 Spare Undulator Production for PAL-XFEL HX1 Beamline 524
 
  • J.H. Han, Y.G. Jung, D.E. Kim, S.J. Lee
    PAL, Pohang, Kyungbuk, Republic of Korea
 
  In the PAL-XFEL hard X-ray beamline, 20 undulator segments with a 26 mm period and a 5 m length are installed and operated for XFEL user service. One spare undulator was manufactured in December 2018. The magnetic measurements and tuning was carried out recently. We report the measurement and tuning results.  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-FEL2019-WEP092  
About • paper received ※ 20 August 2019       paper accepted ※ 25 August 2019       issue date ※ 05 November 2019  
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WEP093 Radiation Damage Monitoring at PAL-XFEL 528
 
  • S.J. Lee, J.H. Hanpresenter, Y.G. Jung, D.E. Kim, G. Mun
    PAL, Pohang, Kyungbuk, Republic of Korea
 
  Pohang Accelerator Laboratory X-ray Free Electron Laser (PAL-XFEL) has two undulator beamlines, one hard and one soft X-ray beamlines. These two undulator beamlines are in operation since 2017. To maintain the FEL radiation property, the B-field properties of PAL-XFEL undulators need to be kept at certain level. Under the 10 GeV beam operation condition, the accumulated radiation can affect the permanent magnet properties of the undulators. However, the radiation damage of permanent magnet can be different by the operation environment and the geometry of the undulator. Accumulated radiation sensors and a miniature undulator with a few periods are installed in the PAL-XFEL hard X-ray undulator line to monitor the undulator radiation damage. In this proceeding, the radiation monitoring activities and the recent measurement results will be introduced.  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-FEL2019-WEP093  
About • paper received ※ 19 August 2019       paper accepted ※ 25 August 2019       issue date ※ 05 November 2019  
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WEP094 Variable-Period Variable-Pole Number Hybrid Undulator Design for Novosibirsk THz FEL 531
 
  • I.V. Davidyuk, O.A. Shevchenko, V.G. Tcheskidov, N.A. Vinokurov
    BINP SB RAS, Novosibirsk, Russia
 
  The undulator developed for the first FEL of Novosibirsk FEL facility employs variable-period structure based on the hybrid undulator scheme with poles splinted into halves. The design was adapted to deliver optimal performance, estimations were made based on results of three-dimensional field simulations. According to the modeling results, the undulator will not only widen significantly the first FEL tuning range moving the long-wavelength border of the first harmonic from 200 µm to 450 µm but also provide wider aperture and increase efficiency at shorter wavelengths.  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-FEL2019-WEP094  
About • paper received ※ 18 August 2019       paper accepted ※ 29 August 2019       issue date ※ 05 November 2019  
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WEP095 The Athos Soft X-Ray Beamlines at SwissFEL 535
 
  • R. Follath, U. Flechsig, L. Patthey, U.H. Wagner
    PSI, Villigen PSI, Switzerland
 
  After the successful start of the hard X-ray FEL at SwissFEL in 2016, the soft X-ray FEL ATHOS at SwissFEL is expected to deliver the first beam by end of 2019. This contribution describes the beamlines attached to the FEL and reports on the status and plans for this soft X-ray facility. The ATHOS facility will operate three end stations. Two stations are already defined and are currently in the design and construction phase whereas the third station will be defined in the future. The first station (AMO) is dedicated to Atomic and Molecular physics as well as nonlinear spectroscopy. It is expected to get light in mid 2020. The second station (Furka) is for condensed matter physics. The beamline consists of a grating monochromator and distributes the beam downstream of the grating chamber by means of horizontal deflecting mirrors. Pink and monochromatic beam operation is foreseen at all branches. The monochromator uses variable line-spacing gratings on spherical substrates with a variable included angle and operates without an entrance slit. Its mechanics is based on the SX-700 design, but with the grating facing up and the mirror facing down. The installation of the beamline will start in August 2019.  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-FEL2019-WEP095  
About • paper received ※ 19 August 2019       paper accepted ※ 29 August 2019       issue date ※ 05 November 2019  
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WEP097 Operational Model of the Athos Undulator Beamline 538
 
  • C. Kittel, M. Calvi, X. Liang, T. Schmidt
    PSI, Villigen PSI, Switzerland
  • N.J. Sammut
    University of Malta, Information and Communication Technology, Msida, Malta
 
  Athos, the new Soft X-ray beamline of SwissFEL, operates 16 Apple X undulators and 15 compact chicanes to implement novel lasing schemes. With the data available after the end of the magnetic measurement campaign (middle 2020), a self-consistent set of equations will be used to summarise all the relevant properties of those devices to start their commissioning. The analytical approach planned will be discussed in great detail and tested with the preliminary experimental data available. Finally, the accuracy of this approach will be evaluated and critically compared to the requirements of the new FEL beamline.  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-FEL2019-WEP097  
About • paper received ※ 27 August 2019       paper accepted ※ 28 August 2019       issue date ※ 05 November 2019  
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WEP098 Advanced Operational Models of the Apple X Undulator 541
 
  • X. Liang, M. Calvi, C. Kittel, T. Schmidt
    PSI, Villigen PSI, Switzerland
  • N.J. Sammut
    University of Malta, Information and Communication Technology, Msida, Malta
 
  Athos is a new soft X-ray beamline at SwissFEL, where the Apple X type undulators will be equipped. These devices are flexible to produce light in different polarization modes. An adequate magnetic field model is required for the operation of undulator. The undulator deflection parameter K and its gradient are calculated starting from the Fourier series of the magnetic field. In the classical parallel and anti-parallel operational modes - respectively elliptical and linear modes, the variation of the magnetic field as well as its parameters are evaluated by computer modeling. The results are compared to the magnetic measurements of the first Apple X prototype.  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-FEL2019-WEP098  
About • paper received ※ 27 August 2019       paper accepted ※ 29 August 2019       issue date ※ 05 November 2019  
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WEP100 Conceptual Design of a Permanent Magnet Undulator for Fast Pulse-to-Pulse Polarization Switching in an FEL 545
 
  • T.Y. Chung, C.-S. Hwang
    NSRRC, Hsinchu, Taiwan
 
  In this paper, we propose the design of an undulator to alter polarization at a fast frequency and the energy spectrum pulse-to-pulse in free-electron lasers (FELs). A fast time varying magnetic field generated in an undulator can alter characteristic light features. An electromagnetic (EM) and permanent magnet (PM) type undulator provides typically a magnetic field switching frequency below 100 Hz. Inductance and heating issues from coils limit the performance for the EM type and favor small magnetic fields and longer periods and for the PM type, strong magnetic forces between magnet arrays create undesired relative motion. In this paper, we discuss these issues and propose an undulator made of Halbach cylinders with rotating magnet arrays to switch the magnetic fields. Concept, magnet structure and performance are discussed in this note.  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-FEL2019-WEP100  
About • paper received ※ 30 July 2019       paper accepted ※ 26 August 2019       issue date ※ 05 November 2019  
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WEP101 Linear Polarisation via a Delta Afterburner for the CompactLight Facility 549
 
  • H.M. Castañeda Cortés, D.J. Dunning, N. Thompson
    STFC/DL/ASTeC, Daresbury, Warrington, Cheshire, United Kingdom
 
  Funding: CompactLight is funded by the European Union’s Horizon 2020 research and innovation program under Grant Agreement No.777431.
We studied the degree of polarisation of the FEL radiation from the diverted-beam scheme [1,2] using the layout of the CompactLight facility, which is in the process of being designed. To satisfy the polarisation requirements defined by the users [3] without compromising the aim of the facility to be compact, we studied a configuration comprising a helical Super Conductive Undulator (SCU) followed by a Delta afterburner (configured to generate linearly polarised light). The trade-offs between the SCU length, afterburner length, degree of polarisation and output power are presented and discussed.
[1] E. A. Schneidmiller and M. V. Yurkov, Phys. Rev. ST Accel. Beams 16, 11702 (2013)
[2] A. Lutman et al., Nature Photonics 10, 468(2016)
[3] A. Mak et al., FREIA Report 2019/01, 2019
 
poster icon Poster WEP101 [1.083 MB]  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-FEL2019-WEP101  
About • paper received ※ 16 August 2019       paper accepted ※ 25 August 2019       issue date ※ 05 November 2019  
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WEP103 A Plasma Attenuator for Soft X-Rays in LCLS-II 553
 
  • A.S. Fisher, A.L. Benwell, Y. Feng, B.T. Jacobson
    SLAC, Menlo Park, California, USA
 
  Attenuation of X-ray FEL beams is often required to avoid damaging optics and detectors during alignment, and to study fluence-dependent effects. Soft X-rays are commonly attenuated by photoabsorption in a gas such as argon. However, absorbing a mJ pulse along a meter creates a pressure wave that drives gas away from the X-ray propagation axis, until equilibrium recovers in ~1 ms. This timescale matched the 120-Hz pulse spacing of LCLS, but at the high repetition rate (up to 1 MHz) and power (up to 200 W) of LCLS-II, the attenuation of subsequent pulses is reduced. Simulations demonstrate hysteresis and erratic attenuation from gas-density depletion. Instead, we propose to replace the gas column with an argon plasma in a TM010 RF cavity. The density profile then is largely set by the RF mode. X-ray absorption becomes a perturbation compared to the energy in the plasma. An LCLS-II solid-state RF amplifier, generating up to 4 kW at 1.3 GHz, can provide the drive, and the FPGA-based low-level RF controller can be programmed to track tuning with plasma density. Several diagnostics are planned to monitor plasma properties over a fill-pressure range of 10 to 1000 Pa.  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-FEL2019-WEP103  
About • paper received ※ 16 August 2019       paper accepted ※ 28 August 2019       issue date ※ 05 November 2019  
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WEP104 A High-Power, High-Repetition Rate THz Source for LCLS-II Pump-Probe Experiments 556
 
  • Z. Zhang, A.S. Fisher, M.C. Hoffmann, Z. Huangpresenter, B.T. Jacobson, P.S. Kirchmann, W.S. Lee, A. Lindenberg, E.A. Nanni, R.W. Schoenlein
    SLAC, Menlo Park, California, USA
  • S. Sasaki, J.Z. Xu
    ANL, Lemont, Illinois, USA
 
  Experiments using a THz pump and an x-ray probe at an x-ray free-electron laser (XFEL) facility like LCLS-II require frequency-tunable (3 to 20 THz), narrow bandwidth ( ∼ 10\%), carrier-envelope-phase-stable THz pulses that produce high fields (>1MV/cm) at the repetition rate of the x rays and well synchronized with them. In this paper, we study a two-bunch scheme to generate THz radiation at LCLS-II: the first bunch produces THz radiation in a permanent-magnet or electromagnet wiggler immediately following the LCLS-II undulator that produces X-rays from the second bunch. The initial time delay between the two bunches is optimized to compensate for the path difference in transport. We describe the two-bunch beam dynamics, the THz wiggler and radiation, as well as the transport system bringing the THz pulses from the wiggler to the experimental hall.  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-FEL2019-WEP104  
About • paper received ※ 23 August 2019       paper accepted ※ 17 September 2019       issue date ※ 05 November 2019  
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WEP107 Polarizing Afterburner for the LCLS-II Undulator Line 560
 
  • H.-D. Nuhn
    SLAC, Menlo Park, California, USA
 
  Funding: This work was supported by U.S. Department of Energy, Office of Basic Energy Sciences, under Contract DE-AC02-76SF00515.
A fixed-gap polarizing undulator (Delta) has been successfully operated in afterburner mode in the LCLS FEL beamline at the SLAC National Accelerator Laboratory (SLAC) from August 2014 to the end of operations of the LCLS facility in December 2018. The LCLS undulator line is currently being replaced by two new undulator lines (as part of the LCLS-II project) to operate in the hard and soft X-ray wavelength ranges. Polarizing afterburners are planned for the end of the soft X-ray (SXR) line. A new polarizing undulator (Delta-II) is being developed for two reasons: (1) increased maximum K value to be resonant over the entire operational range of the SXR beamline (2) variable gap for K value control. It has been shown that using row phase control to reduce the K value while operating in circular polarizing mode severely degrades the performance of a polarizing undulator in afterburner mode. The device is currently scheduled for installation 2020-2021. The paper will explain the need for the variable gap design backed up by beam based measurements done with the LCLS Delta undulator.
 
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-FEL2019-WEP107  
About • paper received ※ 27 August 2019       paper accepted ※ 29 August 2019       issue date ※ 05 November 2019  
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