5. Longitudinal diagnostic and synchronization
Paper Title Page
Femtosecond Synchronization of PAL-XFEL  
  • C. Kim, H.-S. Kang, I.S. Ko, C.-K. Min
    PAL, Pohang, Kyungbuk, Republic of Korea
  The PAL-XFEL achieved a 20 fs jitter in the bunch arrival time at the end of undulators and its pump-probe system, which is extremely useful for maintaining a high stability of machine and time-resolved experiments with high time resolution. A low phase noise timing system and high stability high power RF system enable this low jitter. The measurement result shows 10 fs jitter of bunch arrival time at the injector and it increased ~ 20 fs due to the bunch energy variation. The possibility of improving the final jitter is described based on the optimization of bunch compressors and a longitudinal feedback.  
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WEOA02 Optical Investigation to Minimize the Electron Bunch Arrival-time Jitter Between Femtosecond Laser Pulses and Electron Bunches for Laser-Driven Plasma Wakefield Accelerators 332
  • S. Mattiello, A. Penirschke
    THM, Friedberg, Germany
  • H. Schlarb
    DESY, Hamburg, Germany
  Funding: The work of S. Mattiello is supported by the German Federal Ministry of Education and Research (BMBF) within the Project ' MAKE-PWA.
In a laser driven plasma based particle accelerators a stable synchronization of the electron bunch and of the plasma wakefield in the range of less than 2 fs is necessary in order to optimize the acceleration. For this purpose we are developing a new shot to shot feedback system with a time resolution of less than 1 fs. As a first step, stable THz pulses are generated by optical rectification of a fraction of the plasma generating high energy laser pulses in a nonlinear lithium niobate crystal. It is planed that the generated THz pulses will energy modulate the electron bunches shot to shot before the plasma to achieve the time resolution of 1 fs. In this contribution we systematically investigate the influence of the optical properties as well as the theoretical description of the THz generation on the conversion efficiency of the generation of short THz pulses in undepleted approximation. We compare different approximations for the modeling of the generation dynamics and of the dielectric function in order to investigate the importance of a detailed description of the optical properties. First results by considering intensity decreasing of the laser pump will be presented.
*The feedback system will be tested at the Accelerator R&D facility SINBAD (Short Innovative Bunches and Accelerators at DESY).
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DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IBIC2018-WEOA02  
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WEOA03 First Electro-Optical Bunch Length Measurements from the European XFEL 338
  • B. Steffen, M.K. Czwalinna, C. Gerth, P. Peier
    DESY, Hamburg, Germany
  Three electro-optical bunch length detection systems based on spectral decoding have been installed and are being commissioned at the European XFEL. The systems are capable of recording individual longitudinal bunch profiles with sub-picosecond resolution at a bunch repetition rate 1.13 MHz. 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 this paper, we present first measurement results for the electro-optical detection system located after the second bunch compressor. A preliminary comparison with data from the bunch arrival-time monitor shows good agreement.  
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DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IBIC2018-WEOA03  
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WEOA04 The Application of Beam Arrival Time Measurement at SXFEL 342
  • S.S. Cao, J. Chen, Y.B. Leng, R.X. Yuan
    SINAP, Shanghai, People's Republic of China
  Shanghai soft X-ray free electron laser (SXFEL) is able to generate high brightness and ultra-short light pulses. The generation of the light sources relies on the synchronization between seeded laser and electron bunch. Beam arrival time play an important role to keep the synchronization. For the SXFEL, a beam arrival time resolution under 100 fs is required. In this paper, the application of beam arrival time measurement scheme on SXFEL has been presented. The whole BAM system consists of four parts: beam arrival time monitor, electronic front-end, signal acquisition system, and high-level signal processing and presentation. Currently, four sets of beam arrival time monitors (BAMs) have been installed in the SXFEL and distributed in four different locations. The relevant beam arrival time experiment and beam flight time experiment based on the dual-cavities mixing method have also been performed so as to evaluate and analyze the beam status.  
slides icon Slides WEOA04 [4.588 MB]  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IBIC2018-WEOA04  
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WEPA01 A MicroTCA.4 Timing Receiver for the Sirius Timing System 375
  • J.L. Brito Neto, G.B.M. Bruno, S.R. Marques, L.M. Russo, D.O. Tavares
    LNLS, Campinas, Brazil
  The AMC FMC carrier (AFC) is a MicroTCA.4 AMC board which has a very flexible clock circuit that enables any clock source to be connected to any clock input, including telecom clock, FMC clocks, programmable VCXO oscillator and FPGA. This paper presents the use of the AFC board as an event receiver connected to the Sirius timing system to provide low jitter synchronized clocks and triggers for Sirius BPM electronics and other devices.  
poster icon Poster WEPA01 [3.299 MB]  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IBIC2018-WEPA01  
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WEPA02 Recent Progress of Bunch Resolved Beam Diagnostics for BESSY VSR 379
  • J.G. Hwang, T. Atkinson, P. Goslawski, A. Jankowiak, M. Koopmans, M. Ries, A. Schälicke, G. Schiwietz
    HZB, Berlin, Germany
  • T. Mertens
    Helmholtz-Zentrum Berlin für Materialien und Energie GmbH (HZB), Berlin, Germany
  BESSY VSR is an upgrade project of the existing storage ring BESSY II to create long and short photon pulses simultaneously for all beam lines by installing additional superconducting cavities with harmonic frequencies of 1.5 GHz and 1.75 GHz. The storage-ring operation will be influenced by a transient beam-loading effect of all cavities and by the complex filling pattern due to the disparity in the current of long and short bunches. This, in turn, could introduce a variation of beam trajectory, transverse profile, and length for the different bunches. This stimulates the development of bunch-resolved monitors for bunch length, beam size, filling pattern and beam trajectory displacement. In this paper, we show new developments of crucial beam diagnostics including measurements of the bunch-resolved temporal profile with a resolution of less than 1 ps FWHM and bunch-resolved profile with a resolution of less than 10 um rms. The upgrade of the booster beam-diagnostics will be discussed as well.  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IBIC2018-WEPA02  
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WEPA06 Thermal Coefficient of Delay Measurement of the New Phase Stable Optical Fiber * 383
  • L. Liu, X. Ma, G. Pei
    IHEP, Beijing, People's Republic of China
  The Thermal Coefficient of Delay (TCD) is an essen-tial parameter of optical fiber which determines a fiber's phase transfer stability due to temperature variation. The TCD of a new phase stable single mode optical fiber (YPSOC) from Yangtze Optical Fibre and Cable Compa-ny (YOFC) is measured. The radio frequency (RF) signal is modulated to optical wave by a laser module which is transmitted through the 400-meter long YPSOC to be measured. The returned optical wave is demodulated to RF signal by the photodetector. A phase detector and a data acquisition module (DAQ) are used to acquire the phase difference between the forward and returned sig-nals. Two temperature-stabilized cabinets are designed to maintain and control the ambient temperature of the measurement system. The TCD of less than 10ps/km/K at room temperature is obtained. YPSOC and the meas-urement platform can be applied on signal transmission or measurement system that need to compensate the temperature drift.  
poster icon Poster WEPA06 [0.653 MB]  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IBIC2018-WEPA06  
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WEPA07 Beam Phase Measurement System in CSNS Linac 386
  • P. Li
    IHEP CSNS, Dongguan, People's Republic of China
  • F. Li, T.G. Xu
    IHEP, Beijing, People's Republic of China
  • M. Meng
    DNSC, Dongguan, People's Republic of China
  • J. Peng
    CSNS, Guangdong Province, People's Republic of China
  • W. Peng
    CETC, Shushan, People's Republic of China
  We developed beam phase measurement system ourselves in CSNS (China Spallation Neutron Source). The resolution of the system is less than 0.1° and the accuracy is less than 1°. It played a key role in CSNS Linac commissioning especially in RFQ and DTL commissioning. Further we measured the beam energy by TOF (Time of Flight) method base on this system. The energy accuracy is less than 0.1 MeV.  
poster icon Poster WEPA07 [1.070 MB]  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IBIC2018-WEPA07  
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WEPA09 Long Term Beam Phase Monitoring Based on HOM Signals in SC Cavities at FLASH 388
  • J.H. Wei
    USTC/NSRL, Hefei, Anhui, People's Republic of China
  • N. Baboi
    DESY, Hamburg, Germany
  • L. Shi
    PSI, Villigen PSI, Switzerland
  The accelerating RF fields in superconducting cavities must be controlled precisely in FEL (Free Electron Laser) facilities to avoid beam energy spread and arrival time jitter. Otherwise the beam quality is degraded. The LLRF (Low Level Radio Frequency) system controls the RF field and provides a highly stable RF reference. A new type of beam phase determination technique based on beam-excited HOMs (Higher Order Modes) in cavities has been implemented. The two special couplers installed at both ends of each cavity, pick up the signals containing both the leakage of the accelerating field and the HOM signals. Therefore the signals can be used to calculate the beam phase directly with respect to the RF phase. We analysed the factors which may affect the result of the beam phase on a long-term based on an experimental platform at FLASH. Some phase drifts between the HOM-BPhM (Beam Phase Monitor) and the LLRF system phase measurement were observed and the reason will be further studied.  
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WEPA12 Differential Evolution Genetic Algorithm for Beam Bunch Temporal Reconstruction 392
  • D. Wu, T.H. He, C.L. Lao, P. Li, J. Liu, X. Luo, Q. Pan, L.J. Shan, X. Shen, J. Wang, D.X. Xiao, L.G. Yan, P. Zhang, K. Zhou
    CAEP/IAE, Mianyang, Sichuan, People's Republic of China
  • Y. Liu
    CAEP/IFP, Mainyang, Sichuan, People's Republic of China
  Funding: Work supported by China National Natural Science Foundation of China with grant (11475159, 11505173, 11505174, 11575264, 11605190 and 11105019)
Coherent radiation, such as coherent transition radiation, coherent diffraction radiation, coherent synchrotron radiation, etc, can be used to measure the longitudinal distribution of the electron beam bunch of any length, as long as the coherent radiation spectrum can be measured. In many cases, the Kramers-Krönig relationship is used to reconstruct the temporal distribution of the beam from the coherent radiation spectrum. However, the extrapolation of the low frequency will introduce the uncertainty of the reconstruction. In this paper, an algorithm of differential evolution (DE) for temporal reconstruction is discussed. The DE reconstruction works well for the complex and ultrashort distribution. It will be an effectIve tool to accurately measure the femtosecond bunch temporal structure.
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IBIC2018-WEPA12  
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WEPA13 Electro-Optic Modulator Based Beam Arrival Time Monitor for SXFEL* 396
  • X.Q. Liu, L.F. Hua, L.W. Lai, Y.B. Leng, R.X. Yuan
    SINAP, Shanghai, People's Republic of China
  • N. Zhang
    SSRF, Shanghai, People's Republic of China
  Beam arrival time monitor (BAM) is an important tool to investigate the temporal characteristic of elec-tron bunch in free electron laser (FEL) like Shanghai soft X-ray Free Electron Laser (SXFEL). Since the timing jitter of electron bunch will affect the FEL's stability and the resolution of time-resolved experi-ment at FELs, it is necessary to precisely measure the electron bunch arrival time so as to reduce the timing jitter of the electron bunch with beam based feedback. The beam arrival time monitor based on electro-optic modulator (EOM) is already planned and will be de-veloped and tested at SXFEL in the next three years. Here the design and preliminary results of the EOM based beam arrival time monitor will be introduced in this paper.  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IBIC2018-WEPA13  
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WEPA15 Development of BAM Electronics in PAL-XFEL 400
  • D.C. Shin, J.H. Hong, H.-S. Kang, C. Kim, G. Kim, C.-K. Min
    PAL, Pohang, Republic of Korea
  We describe an electronics for electron bunch arrival time monitor (BAM) with a less than 10 femtosecond resolution, which was developed in 2017 and is currently in use at PAL-XFEL. When electron bunches go through an S-band monopole cavity, about 1 us long RF signal can be obtained to compare with a low phase noise RF reference. The differential phase jitter corresponds to the arrival time jitter of electron bunches. RF front-end (F/E) which converts the S-band pickup signal to intermediate frequency (IF) signal, is the essential part of a good time resolution. The digitizer and the signal processor of the BAM electronics are installed in an MTCA platform. This paper presents the design scheme, test results of the BAM electronics and future improvement plans.  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IBIC2018-WEPA15  
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WEPA16 Micro-Bunching Instability Monitor for X-ray Free Electron Laser 404
  • C. Kim, H.-S. Kang, G. Kim, I.S. Ko
    PAL, Pohang, Kyungbuk, Republic of Korea
  • J.H. Ko
    POSTECH, Pohang, Kyungbuk, Republic of Korea
  A direct method was developed to measure the micro-bunching instability in the X-ray Free Electron Laser (XFEL). The micro-bunching instability comes from the interaction between the electron beam and the coherent synchrotron radiation (CSR), and the FEL intensity can be affected significantly by the micro-bunching instability. However, no effective method had been introduced to monitor the micro-bunching instability, so that we installed a CCD camera to measure the micro-bunching instability after the bunch compressor. The CCD camera showed the micro-bunching instability successfully, and more interesting features of the micro-bunching instability were revealed from it.  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IBIC2018-WEPA16  
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WEPA17 Development, Fabrication and Laboratory Tests of Bunch Shape Monitors for ESS Linac 407
  • S.A. Gavrilov, D.A. Chermoshentsev, A. Feschenko
    RAS/INR, Moscow, Russia
  Two Bunch Shape Monitors have been developed and fabricated in INR RAS for European Spallation Source linac. To fulfil the requirements of a 4 ps phase resolution the symmetric λ-type RF-deflector based on the parallel wire line with capacitive plates has been selected. Additional steering magnet to correct incline of the focused electron beam is also used. Limitations due to space charge of the analysed beam and due to external magnetic fields are discussed. The results of the laboratory tests of the monitors are presented.  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IBIC2018-WEPA17  
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WEPA18 Development of Longitudinal Beam Profile Diagnostics for Beam-beam Effects Study at VEPP-2000 410
  • M.V. Timoshenko, V.M. Borin, O.I. Meshkov, Yu. A. Rogovsky, D.B. Shwartz, Yu.M. Zharinov
    BINP SB RAS, Novosibirsk, Russia
  • V.L. Dorokhov
    BINP, Novosibirsk, Russia
  The comprehensive development of beam longitudinal profile measurement systems based on stroboscopic optical dissector has started at VEPP-2000 electron-positron collider complex. The dissector was setted and commissioned at booster ring BEP that was deeply upgraded (2013-2015) to achieve top energy of 1 GeV. Bunch lengthening with current was studied at BEP with its new RF-cavity. In addition the method of synchrotron frequency measurement by dissector was applied. After dissector checkouts at BEP the similar studies were carried out with a single beam at VEPP-2000 storage ring in parallel with streak-camera measurements. Good agreement of results was observed. Series of single-turn longitudinal and vertical bunch profiles snapshots was made by streak-camera with respect to delay after counter beam injection. The unexpected longitudinal beam dynamics was observed for intensities above the beam-beam threshold. These studies together with beam-beam coherent oscillations spectra seen by pickups are of a great interest for understanding of flip-flop phenomenon which establish a fundamental luminosity limit at VEPP-2000 operating with round beams.  
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WEPA19 Results from the CERN LINAC4 Longitudinal Bunch Shape Monitor 415
  • J. Tan, G. Bellodi
    CERN, Geneva, Switzerland
  • A. Feschenko, S.A. Gavrilov
    RAS/INR, Moscow, Russia
  The CERN Linac4 has been successfully commissioned to its nominal energy and will provide 160 MeV H ions for charge-exchange injection into the Proton Synchrotron Booster (PSB) from 2020. A complete set of beam diagnostic devices has been installed along the accelerating structures and the transfer line for safe and efficient operation. This includes two longitudinal Bunch Shape Monitors (BSM) developed by the Institute for Nuclear Research (INR, Moscow). Setting-up the RF cavities of Linac4 involves beam loading observations, time-of-flight measurements and reconstruction of the longitudinal emittance from phase profile measurements. In this paper the BSM is presented along with some results obtained during accelerator commissioning, including a comparison with phase measurements performed using the Beam Position Monitor system.  
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WEPA20 First Results From the Bunch Arrival-Time Monitors at SwissFEL 420
  • V.R. Arsov, P. Chevtsov, S. Hunziker, M.G. Kaiser, D. Llorente Sancho, A. Romann, V. Schlott, M. Stadler, D.M. Treyer
    PSI, Villigen PSI, Switzerland
  • M. Dach
    Dach Consulting GmbH, Brugg, Switzerland
  Two Bunch Arrival-Time Monitors (BAM), based on fiber optical Mach-Zehnder intensity modulators, which encode the arrival-time information in the amplitude of the laser pulses delivered through a highly stable pulsed optical reference distribution system, have been commissioned and are operational at SwissFEL. The first BAM is at the RF-Gun, the second one is downstream the first bunch compressor. Both BAMs operate simultaneously and measure the arrival-time drift and jitter with less than 5 fs resolution. For the first time we have experimentally verified the excellent SwissFEL bunch stability. We have developed concepts and tested hardware, which enhance the commissioning and user operation. In particular we have successfully tested a tool for fast timing overlap between the electron bunch and the reference laser pulse, which allows fast system set-up and characterization. We have verified the capability for 2-bunch and 100 Hz operation. In comparison to the prototype detectors, which were operational at the SwissFEL test injector, we have achieved an improved BAM resolution in the range 10 pC - 200 pC.  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IBIC2018-WEPA20  
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Temporal Diagnostics of Femtosecond Electron Bunches via X-ray Intensity Interferometry  
  • I. Inoue, T. Hara, Y. Inubushi, H. Tanaka, M. Yabashi
    RIKEN SPring-8 Center, Sayo-cho, Sayo-gun, Hyogo, Japan
  Optical pulses and particle beams with ultrashort temporal duration have been powerful probes for capturing ultrafast processes. An X-ray free-electron laser (XFEL) based on the self-amplified spontaneous emission scheme is a newly developed ultrafast light source with femtosecond duration. The ultrafast XFEL pulses are generated from the electron bunches (e-bunches) that are accelerated to a relativistic speed with strong compression to a femtosecond regime. Evaluation of the temporal profile of the e-bunch is therefore essential for optimizing accelerator parameters for achieving XFEL amplification, as well as for characterizing the XFEL pulse duration. As a new temporal diagnostic scheme for e-bunches, we recently propose an X-ray intensity interferometry using spontaneous X-ray beam generated by the e-bunch [1]. In this presentation, I will talk about the concept of the X-ray intensity interferometry for determination of ultrashort e-bunch duration. Also, I will report on the temporal diagnostics of 8.1-GeV e-bunch at SPring-8 Angstrom compact free-electron LAser (SACLA) using the X-ray intensity interferometry.
[1] I. Inoue, T. Hara, Y. Inubushi, K. Tono, T. Inagaki, T. Katayama, Y. Amemiya, H. Tanaka, and M. Yabashi, Phys. Rev. Acc. Beams, in press.
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