Longitudinal diagnostics and synchronisation
Paper Title Page
Terahertz-Based Sub-femtosecond Metrology of Relativistic Electron Beams  
  • R.K. Li
    TUB, Beijing, People’s Republic of China
  High brightness, ultrashort electron beams are driving various advanced scientific instruments. As we push the limits of electron beams in the time domain, the challenges include not only generating the shortest possible pulse durations, but also precisely controlling or characterizing the timing of electron beams relative to optical pulses. The optical pulses can be for example the pump laser in ultrafast electron diffraction, or the drive laser in external-injection laser plasma accelerators, etc. It is not feasible to characterize the timing between electron and laser pulses to fs level using an rf-based approach, due to the phase jitter of rf sources relative to lasers. With a laser-generated THz streaking field, the timing of electron beams can be determined at sub-fs level and the pulse duration at single fs level on a shot-by-shot basis. Showing that THz compression can significantly reduce the pulse duration and intrinsically stabilize the timing jitter of electron beams. We believe that time-domain manipulation of relativistic electron beams using laser-generated THz can significantly boost the performance of electron beam-based instruments for ultrafast science.  
slides icon Slides TUCO01 [19.114 MB]  
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TUCO02 Experimental Observation of Submillimeter Coherent Cherenkov Radiation at CLARA Facility 256
  • K.V. Fedorov, P. Karataev, A.N. Oleinik
    JAI, Egham, Surrey, United Kingdom
  • K.V. Fedorov, A. Potylitsyn, A. Potylitsyn
    TPU, Tomsk, Russia
  • P. Karataev
    Royal Holloway, University of London, Surrey, United Kingdom
  • A.N. Oleinik
    BelSU, Belgorod, Russia
  • T.H. Pacey, Y.M. Saveliev
    STFC/DL/ASTeC, Daresbury, Warrington, Cheshire, United Kingdom
  • T.H. Pacey
    UMAN, Manchester, United Kingdom
  • Y.M. Saveliev
    Cockcroft Institute, Warrington, Cheshire, United Kingdom
  Nowadays, the method of longitudinal beam profile diagnostic based on transition radiation (TR) spectrum is well studied [1] and is constantly being applied, while using of coherent Cherenkov radiation (CCR) is a modern task that opens up new possibilities in this area [2]. In current work we conducted experiments on CCR generation, observation and it further spectral analysis at 0.1-30 THz spectral range. All experimental work was at CLARA (beam area 1) facility (~50 MeV beam energy at up to 10 Hz pulse repetition rate with sub-ps bunch length). Inside of vacuum chamber we developed movable platform where both VCR and TR target were placed, which is allows us to observe both effects during one accelerator run. For spectral analysis we used Martin-Pupplet interferometer as it provides higher signal to noise ratio and allows us to perform instabilities normalisation. As a result we will demonstrate a selection of interferograms and spectrums (as well as reconstructed longitudinal beam profiles) for different machine setups and distances between charged particle beam and Cherenkov target. By using mathematical analysis it has been shown that CLARA bunch length was about 1.2 ps.  
slides icon Slides TUCO02 [22.952 MB]  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IBIC2019-TUCO02  
About • paper received ※ 03 September 2019       paper accepted ※ 10 September 2019       issue date ※ 10 November 2019  
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Upgraded Bunch Arrival-Time Monitors for the European XFEL Reaching Below 3fs Time Resolution  
  • M.K. Czwalinna, C. Gerth, H. Schlarb, B. Steffen
    DESY, Hamburg, Germany
  Free electron laser facilities, such as the European XFEL and FLASH, have increasingly high demands on the temporal stability of the electron bunches, as pump-probe experiments meanwhile aim for timing stabilities of few femtoseconds residual jitter only. For a beam-based feedback control of the linear accelerator, bunch arrival-time monitors are required that are capable of reaching measurement resolutions better than the stated timing stability goals. We report on our electro-optical bunch arrival-time monitors now achieving a time resolution better than 3 fs. This new level of precision is a first step towards the ultimate goal of reaching sub-femtosecond timing stability. The system has also been upgraded to allow for multi-beam line operation with large variations of the bunch arrival times for the different pulse trains. The characteristics of the bunch arrival-time monitor system and limitations of the state-of-the-art design will be discussed.  
slides icon Slides TUCO03 [2.481 MB]  
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TUCO04 Longitudinal Phase Space Reconstruction for the Heavy Ion Accelerator HELIAC 261
  • S. Lauber, K. Aulenbacher, W.A. Barth, C. Burandt, F.D. Dziuba, V. Gettmann, T. Kürzeder, J. List, M. Miski-Oglu
    HIM, Mainz, Germany
  • K. Aulenbacher, W.A. Barth, C. Burandt, F.D. Dziuba, P. Forck, V. Gettmann, M. Heilmann, T. Kürzeder, S. Lauber, J. List, M. Miski-Oglu, A. Rubin, T. Sieber, S. Yaramyshev
    GSI, Darmstadt, Germany
  • K. Aulenbacher
    KPH, Mainz, Germany
  • F.D. Dziuba, S. Lauber, J. List
    IKP, Mainz, Germany
  • H. Podlech, M. Schwarz
    IAP, Frankfurt am Main, Germany
  At the GSI Helmholtzzentrum für Schwerionenforschung in Darmstadt, Germany, a prototype cryomodule (Advanced Demonstrator) for the superconducting (SC) continuous wave (CW) Helmholtz Linear Accelerator (HELIAC) is under construction. A transport line, comprising quadrupole lenses, rebuncher cavities, beam correctors and sufficient beam instrumentation has been built to deliver the beam from the GSI 1.4 MeV/u High Charge Injector (HLI) to the Advanced Demonstrator, which offers a test environment for SC CW multigap cavities. In order to achieve proper phase space matching, the beam from the HLI must be characterized in detail. In a dedicated machine experiment the bunch shape has been measured with a non destructive bunch shape monitor (BSM). The BSM offers a sufficient spatial resolution to use it for reconstruction of the energy spread. Therefore, different bunch projections were obtained by altering the voltage of two rebunchers. These measurements were combined with dedicated beam dynamics simulations using the particle tracking code Dynamion. The longitudinal bunch shape and density distribution at the beginning of the matching line could be fully characterized.  
slides icon Slides TUCO04 [1.810 MB]  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IBIC2019-TUCO04  
About • paper received ※ 30 August 2019       paper accepted ※ 08 September 2019       issue date ※ 10 November 2019  
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Measurement of Electron Pulse Length at 35 MeV Using a Terahertz Split Ring Resonator  
  • X.Y. Liu
    USTC/NSRL, Hefei, Anhui, People’s Republic of China
  • M.M. Dehler, V. Guzenko, R. Ischebeck, X.Y. Liu, C. Lombosi, V. Schlott
    PSI, Villigen PSI, Switzerland
  • T. Feurer, M. Hayati, Z. Ollmann
    Universität Bern, Institute of Applied Physics, Bern, Switzerland
  • V. Georgiadis, D.M. Graham, M.T. Hibberd
    The University of Manchester, The Photon Science Institute, Manchester, United Kingdom
  • A.L. Healy, S.P. Jamison
    Cockcroft Institute, Lancaster University, Lancaster, United Kingdom
  • D. Lake
    University of Manchester, Manchester, United Kingdom
  • T.H. Pacey
    STFC/DL/ASTeC, Daresbury, Warrington, Cheshire, United Kingdom
  • D. Rohrbach
    University of Bern, Bern, Switzerland
  Funding: This work was supported by the European Union’s Horizon 2020 Research and Innovation Programme (730871). X.Y. Liu was supported by China Scholarship Council for a 2-year study at PSI (201706340057).
The resolution of a streak camera system strongly depends on the slew rate of the deflecting element, which is the product of the amplitude and frequency of the device. An attractive approach towards femtosecond and sub-femtosecond range consists in using terahertz-driven devices, which offer a good combination of high frequency and high gradient-gradients of GV/m have been demonstrated in split ring resonator using pulse created by rectifying ultrashort laser pulses. We present results obtained from a beam experiment at the VELA facility at Daresbury laboratory. We tested a planar resonator derived from the geometry of a split ring resonator with an aperture for the beam of 20 um.
Email address: xiaoyu.liu@psi.ch
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WEPP018 THz Generation by Optical Rectification for a Novel Shot to Shot Synchronization System Between Electron Bunches and Femtosecond Laser Pulses in a Plasma Wakefield Accelerator 548
  • 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.
We investigate the influence of the optical properties and of the theoretical description of the THz generation on the conversion efficiency of the generation of short THz pulses. The application is a feedback-system for SINBAD with a time resolution of less than 1 fs for the synchronization of the electron bunch and of the plasma wake field in a laser driven plasma particle accelerator*. Here 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. Then the generated THz pulses will energy modulate the electron bunches shot to shot before the plasma to achieve the required time resolution. In this contribution we compare different approximations for the modeling of the generation dynamics using second order or first order equations as well as considering pump depletion effects. Additionally, the dependence of the efficiency of the THz generation on the choice of the dielectric function has been investigated.
*The feedback system will be tested at the Accelerator R&D facility SINBAD (Short Innovative Bunches and Accelerators at DESY).
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IBIC2019-WEPP018  
About • paper received ※ 04 September 2019       paper accepted ※ 09 September 2019       issue date ※ 10 November 2019  
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WEPP019 Concept of a Novel High-Bandwidth Arrival Time Monitor for Very Low Charges as a Part of the All-Optical Synchronization System at ELBE 553
  • A. Penirschke
    THM, Friedberg, Germany
  • W. Ackermann
    TEMF, TU Darmstadt, Darmstadt, Germany
  • M.K. Czwalinna, H. Schlarb
    DESY, Hamburg, Germany
  • M. Kuntzsch
    HZDR, Dresden, 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 a few fs only. The CW operated electron accelerator ELBE at the Helmholtzzentrum Dresden Rossendorf uses a all-optical synchronization system to ensure a timing stability on the few 10 fs scale. ELBE requires a minimum beam pipe diameter of 43mm that limits the achievable output voltage of the pickup structure to drive the attached electro-optical modulator. This contribution presents a concept for a novel high-bandwidth arrival time monitor with sufficient output signal for the attached EOMs for very low charges as a part of the all-optical synchronization system at ELBE.
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IBIC2019-WEPP019  
About • paper received ※ 04 September 2019       paper accepted ※ 10 September 2019       issue date ※ 10 November 2019  
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WEPP020 First results on Femtosecond Level Photocathode Laser Synchronization at the SINBAD Facility 557
  • M. Titberidze, M. Felber, T. Kozak, T. Lamb, J. Müller, H. Schlarb, S. Schulz, C. Sydlo, F. Zummack
    DESY, Hamburg, Germany
  SINBAD, the "short-innovative bunches and accelerators at DESY" is an accelerator research and development facility which will host various experiments. SINBAD-ARES linac is a conventional S-band linear accelerator which will be capable of producing ultra-short electron bunches with duration of few femtoseconds and energy of up to 100 MeV. In order to fully utilize the potential of ultra-short electron bunches while probing the novel acceleration techniques (e.g. external injection in LWFA), it is crucial to achieve femtosecond level synchronization between photocathode laser and RF source driving the RF gun of the ARES linac. In this paper we present the first results on the synchronization of the near-infrared photocathode laser to the RF source with the residual timing jitter performance of ~10 fs rms. These results were obtained using a conventional laser-to-RF synchronization setup employing heterodyne detection of an RF signal generated by impinging the laser pulses to a fast photodetector. In addition, we describe an advanced laser-to-RF phase detection scheme as a future upgrade; promising even lower timing jitter and most importantly the long-term timing drift stability.  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IBIC2019-WEPP020  
About • paper received ※ 04 September 2019       paper accepted ※ 10 September 2019       issue date ※ 10 November 2019  
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WEPP021 Machine Learning Image Processing Technology Application in Bunch Longitudinal Phase Data Information Extraction 561
  • X.Y. Xu, Y.M. Zhou
    SINAP, Shanghai, People’s Republic of China
  • Y.B. Leng, Y.M. Zhou
    SSRF, Shanghai, People’s Republic of China
  • X.Y. Xu
    University of Chinese Academy of Sciences, Beijing, People’s Republic of China
  To achieve the bunch-by-bunch longitudinal phase measurement, Shanghai Synchrotron Radiation Facility (SSRF) has developed a high resolution measurement system. We used this measurement system to study the injection transient process, and obtained the longitudinal phase of the refilled bunch and the longitudinal phase of the original stored bunch. A large number of parameters of the synchronous damping oscillation are included in this large amount of longitudinal phase data, which are important for the evaluation of machine state and bunch stability. The multi-turn phase data of a multi-bunch is a large two-dimensional array that can be converted into an image. The convolutional neural network (CNN) is a machine learning model with strong capabilities in image processing. We hope to use the convolutional neural network to process the longitudinal phase two-dimensional array data, and extract important parameters such as the oscillation amplitude and the synchrotron damping time.  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IBIC2019-WEPP021  
About • paper received ※ 23 August 2019       paper accepted ※ 10 September 2019       issue date ※ 10 November 2019  
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WEPP022 A Method of Correcting the Beam Transverse Offset for the Cavity Bunch Length Monitor 565
  • Q. Wang, Q. Luo, B.G. Sun
    USTC/NSRL, Hefei, Anhui, People’s Republic of China
  Funding: Supported by National Key R&D Program of China (Grant No. 2016YFA0401900 and No. 2016YFA0401903) and The National Natural Science Foundation of China (Grant No. U1832169 and No. 11575181)
Cavity bunch length monitor uses monopole modes excited by bunches within the cavities to measure the bunch longitudinal root mean square (rms) length. It can provide a very high accuracy and high resolution. However, when the bunch passes through the cavities with transverse offset (that is, the bunch moves off the cavity axis), the amplitude of the monopole modes will change and cannot reflect the bunch length precisely. In this paper, a method of correcting the beam transverse offset is proposed. Simulation results show that the method can reduce the error of the bunch length measurement significantly.
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IBIC2019-WEPP022  
About • paper received ※ 03 September 2019       paper accepted ※ 10 September 2019       issue date ※ 10 November 2019  
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WEPP025 A Transverse Deflecting Cavity Prototype for the MAX IV LINAC 568
  • D. Olsson, A. Bjermo, L. Christiansson, J. Lundh, D. Lundström, E. Mansten, M. Nilsson, E. Paju, L.K. Roslund, K. Åhnberg
    MAX IV Laboratory, Lund University, Lund, Sweden
  The MAX IV LINAC operates both as a full-energy injector for two electron storage rings, and as a driver for a Short Pulse Facility (SPF). There are also plans to build Soft X-ray Laser (SXL) beamlines at the end of the existing LINAC. For SPF and SXL operation, it is important to characterize beam parameters such as bunch profile, slice energy spread and slice emittance. For these measurements, two 3 m long transverse deflecting RF structures are being developed. The structures are operating at S-band, and it is possible to adjust the polarization of the deflecting fields. In order to verify the RF concept, a short 9-cell prototype was constructed. The measurements results of the prototype are presented in this paper.  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IBIC2019-WEPP025  
About • paper received ※ 03 September 2019       paper accepted ※ 09 September 2019       issue date ※ 10 November 2019  
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WEPP026 Electron Bunch Compression Monitors for Short Bunches - Commissioning Results from SwissFEL 571
  • F. Frei, R. Ischebeck
    PSI, Villigen PSI, Switzerland
  In SwissFEL, by using three magnetic chicanes, 3ps long electron bunches can by compressed by a factor of more than 100 down to a few fs in order to generate ultra short X-ray pulses. In order to meet the envisaged beam performance, noninvasive longitudinal diagnostic after each compression stage is essential. These bunch compression monitors measure relative bunch length changes on a shot-to-shot basis by detecting coherent edge, synchrotron or diffraction radiation emitted by the electron bunches. While after the first two magnetic chicanes, a wide spectral part is integrated on a single broadband detector, an infrared spectrometer installed after the third magnetic chicane is providing more detailed information. Here, we will mainly report on commissioning results of the third bunch compression monitor for electron bunches of a few fs.  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IBIC2019-WEPP026  
About • paper received ※ 03 September 2019       paper accepted ※ 10 September 2019       issue date ※ 10 November 2019  
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THBO01 Machine Learning-Based Longitudinal Phase Space Prediction of Two-Bunch Operation at FACET-II 678
  • C. Emma, A.L. Edelen, M.J. Hogan, B.D. O’Shea, V. Yakimenko
    SLAC, Menlo Park, California, USA
  • A. Hanuka
    Technion, Haifa, Israel
  Funding: This work was supported by the U.S. Department of Energy under Contract No. DEAC02-76SF00515
We report on the application of machine learning (ML) methods for predicting the longitudinal phase space (LPS) distribution of particle accelerators. Our approach consists of training a ML-based virtual diagnostic to predict the LPS using only nondestructive linac and e-beam measurements as inputs. We validate this approach with a simulation study for the FACET-II linac and with an experimental demonstration conducted at LCLS. At LCLS, the e-beam LPS images are obtained with a transverse deflecting cavity and used as training data for our ML model. In both the FACET-II and LCLS cases we find good agreement between the predicted and simulated/measured LPS profiles, an important step towards showing the feasibility of implementing such a virtual diagnostic on particle accelerators in the future.
* C. Emma, A. Edelen, M. J. Hogan, B. O’Shea, G. White, and V. Yakimenko., PRAB 21, 112802 (2018)
** A. Scheinker, A. Edelen, D. Bohler, C. Emma, A. Lutman., PRL 121, 044801 (2018)
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IBIC2019-THBO01  
About • paper received ※ 04 September 2019       paper accepted ※ 10 September 2019       issue date ※ 10 November 2019  
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