Electron Diagnostics, Timing, Controls
Paper Title Page
Characterization of High-Brightness Electron Beams at the Frontiers of Temporal and Spatial Resolution  
  • R. Tarkeshian, T. Feurer, M. Hayati, Z. Ollmann
    Universität Bern, Institute of Applied Physics, Bern, Switzerland
  • T. Garvey, R. Ischebeck, E. Prat, S. Reiche, V. Schlott
    PSI, Villigen PSI, Switzerland
  • P. Krejcik
    SLAC, Menlo Park, California, USA
  • W. Leemans, R. Lehé, S. Steinke
    LBNL, Berkeley, California, USA
  We present two novel diagnostics to characterize high-brightness electron beams. The first technique, based on the tunnel ionization of a neutral gas by the intense (GV/m) self-field of the electron beam, can be used to measure the volumetric charge density of the beam, for example to reconstruct pulse durations shorter than few femtoseconds or to measure transverse beam sizes below the micron level. Experiments with sub-femtosecond unipolar self-field of electron beam, that approach the through-the-barrier tunneling times, could further deepen our understanding of quantum tunneling process. The second method can be used to streak electron beams with single cycle THz radiation concentrated in a micrometer gap of a resonant antenna, creating an enhanced electric near-field distribution. With this diagnostic one can measure with sub-femtosecond resolution the longitudinal duration, the slice emittance and energy spread of beams with energies up to tens of MeV. We show the validity of both methods with analytical calculations and particle-in-cell code simulations. We finally present practical implementation of both diagnostics at LCLS, in the XLEAP* experiment, and BELLA.
* X-Ray Laser Enhanced Altosecond Pulse Generation (XLEAP) For LCLS.
Characterization of Electron Bunches in Ultrafast Electron Diffraction Beamlines at KAERI  
  • H.W. Kim, I.H. Baek, K.H. Jang, Y.U. Jeong, K. Lee, J.H. Nam, N.A. Vinokurov
    University of Science and Technology of Korea (UST), Daejeon, Republic of Korea
  • I.H. Baek, B.A. Gudkov, B. Han, K.H. Jang, Y.U. Jeong, H.W. Kim, Y.-C. Kim, K. Lee, S.V. Miginsky, J.H. Nam, S. Park, S. Setiniyaz
    KAERI, Daejon, Republic of Korea
  • R. Fabian, H. Ihee, J. Kim, K.Y. Oang, H. Yang
    KAIST, Daejeon, Republic of Korea
  • K.W. Kim
    Chung Buk National University, Cheongju, Republic of Korea
  • S.V. Miginsky, N.A. Vinokurov
    BINP SB RAS, Novosibirsk, Russia
  Ultrashort electron bunches from ultrafast electron diffraction (UED) beamlines at the Korea Atomic Energy Research Institute (KAERI) has been characterized for sub-100-femtosecond-accuracy time-resolved diffraction experiments. The UED beamlines are designed to deliver electron bunches of 30 fs (rms) duration and 10 fs (rms) timing fluctuation with pumping laser pulses. We have two UED beamlines for solid and gas-phase samples. The energy of the electron beam is ~3 MeV and the bunch charge is more than 1 pC. We measured single-shot and multi-shot electron diffraction patterns of single-crystalline-silicon and poly-crystalline-gold films to confirm the electron beam quality. The temporal characteristics of the electron bunches are investigated by using laser-induced ponderomotive deflecting and spectral decoding of coherent transition radiation from the electron bunch by pumping IR pulse.  
WEB03 R&D at SLAC on Nanosecond-Range Multi-MW Systems for Advanced FEL Facilities 1
  • A.K. Krasnykh, A.L. Benwell, T.G. Beukers, D.F. Ratner
    SLAC, Menlo Park, California, USA
  Funding: Work supported by US Department of Energy contract DE-AC02-76SF00515
A nanosecond-range, multi-MW system containing TEM mode electrodynamic structures fed by controllable pulsers are needed for (1) fast injection systems in multi-bend achromat upgraded (MBA-U) storage rings and for (2) arrays of FEL beamlines powered by a superconducting linear accelerators operating with MHz-bunch repetition rate. The R&D effort covers both type (1) and (2) layouts. This report discuss the experimental results of several concepts for a generation of the nanosecond range multi MW pulsers. Compression of the initially formed electromagnetic (EM) power is employed for a generation of the nanosecond pulses in all concepts discussed here. A solid-state nonlinear media assists the EM compression. Features of the materials and components used in the design will be presented. The results will be included in the design of the kicker systems for advanced FEL facilities. For example, in the LCLS-II, the nanosecond range pulse allows for distributing closely spaced bunches to multiple undulators allowing experimenters to take advantage of combining different colored x-rays.
slides icon Slides WEB03 [1.864 MB]  
WEB04 Laser-to-RF Synchronization with Femtosecond Precision 1
  • T. Lamb, Ł. Butkowski, E.P. Felber, M. Felber, M. Fenner, S. Jabłoński, T. Kozak, J.M. Müller, P. Prędki, H. Schlarb, C. Sydlo, M. Titberidze, F. Zummack
    DESY, Hamburg, Germany
  Optical synchronization systems are already in regular operation in many FELs, or they will eventually be implemented in the future. In FLASH and the European XFEL, phase-stable optical reference signals are provided by a pulsed optical synchronization system in order to achieve low timing jitter FEL performance. The generation of phase-stable RF signals from a pulsed optical synchronization system is still a field of active research. The optical reference module (REFM-OPT), designed at DESY for operation in both FELs, employs a laser-to-RF phase detector, based on an integrated Mach-Zehnder interferometer. The phase drift of the 1.3 GHz RF reference signals with respect to the optical pulses is measured and actively corrected within the REFM-OPT at multiple locations in the accelerator. Therefore the REFM-OPT provides phase stable 1.3 GHz RF reference signals at these locations. The short-term and long-term performance in the accelerator tunnel of the European XFEL is presented and carefully reviewed.  
slides icon Slides WEB04 [5.679 MB]  
ICS Diagnostic of FEL's Electron Beam Based on 6D Wigner Function Approach  
  • A. Malyzhenkov, N.A. Yampolsky
    LANL, Los Alamos, New Mexico, USA
  We report on the design of the Inverse Compton Scattering (ICS) based diagnostic system for the electron beam in the free electron laser. Novel 6D Wigner function ICS theory analytically relates the phase space of emitted radiation to the phase space of the electron beam at the interaction point. Based on this theory, we find signatures of the electron beam phase space features in the emitted ICS radiation. Then, we analyze which of these signatures can be measured in the existing experimental setups and compare reconstructed electron beam phase space features to simulation results from the beam tracking codes. Finally, we inverse the 6D Wigner function ICS theory to find the electron phase space distribution dependence on characteristics of emitted radiation and propose the design of the new diagnostic system to reconstruct desirable 2D projections of the 6D electron phase space.  
WEP027 Numerical Study of Cherenkov Radiation From Thin Silica Aerogel 1
  • H. Hama, K. Nanbu, H. Saito, Y. Saito
    Tohoku University, Research Center for Electron Photon Science, Sendai, Japan
  Funding: This work was supported by JSPS KAKENHI Grant Numbers JP15K13394 and JP17H01070.
Cherenkov radiation (CR) emitted from low-refractive index material such as silica-aerogel is a useful tool for electron beam diagnostics because the opening angle (Cherenkov angle) is small and the CR can be transported onto a detector located far from the radiator. We have prepared a thin (1-mm thick) hydrophobic silica-aerogel with a refractive index of 1.05 that has been developed at Chiba University.* Since the intensity of CR is much stronger than that of optical transition radiation, the CR is a better light source for low-intensity beam diagnostics. In order to apply the CR to measurements of a bunch length of electron beams, we have investigated sources of finite time resolution by a numerical simulation study using the Liénard-Wiechert potentials. We will report results of simulations such as pulse duration of CR and discuss what deteriorates the time resolution.
* M. Tabata et al., Nucl. Instr. and Meth. A 668 (2012) 64.
WEP029 Recent Experimental Results on High-Peak-Current Electron Bunch and Bunch Trains Interacting With a THz Undulator 1
  • X.L. Su, Y. C. Du, W. Gai, W.-H. Huang, Y.F. Liang, C.-X. Tang, D. Wang, L.X. Yan
    TUB, Beijing, People's Republic of China
  Funding: supported by the National Natural Science Foundation of China (NSFC Grants No. 11475097) and National Key Scientific Instrument and Equipment Development Project of China (Grants No. 2013YQ12034504).
In this paper, experimental results based on THz undulator with widely tunable gap installed at Tsinghua Thomson scattering X-ray (TTX) beamline are introduced. This is a planar permanent magnetic device with 8 regular periods, each 10 cm long. The undulator parameter varies from 9.24-1.39 by changing the magnetic gap from 23mm to 75mm. The coherent undulator radiation can be used as a narrow-band THz source with central frequency ranging from 0.4 THz to 10 THz. The bunch length was figured out from the radiation intensity at different undulator gap, which agreed well with simulations. Furthermore, slice energy modulation was directly observed when high-peak-current bunch trains based on nonlinear longitudinal space charge oscillation passed through the undulator. The demonstrated experiment in THz regime provides a significant scaled tool for FEL mechanism exploration owing to the simplicity of bunch modulation and diagnostics in this range.
* Corresponding author: yanlx@mail.tsinghua.edu.cn
WEP030 Large-Scale Turnkey Timing Distribution System for New Generation Photon Science Facilities 1
  • K. Shafak
    CFEL, Hamburg, Germany
  • A. Berg, F.X. Kärtner, A. Kalaydzhyan, J. Meier, D. Schimpf, T. Tilp
    Deutsches Elektronen Synchrotron (DESY) and Center for Free Electron Science (CFEL), Hamburg, Germany
  • A. Berlin, E. Cano, H.P.H. Cheng, A. Dai, J. Derksen, D. Forouher, W. Nasimzada, M. Neuhaus, P. Schiepel, E. Seibel
    Cycle GmbH, Hamburg, Germany
  We report a large-scale turnkey timing distribution system able to satisfy the most stringent synchronization requirements demanded by new generation light sources such as X-ray free-electron lasers and attoscience centers. Based on the pulsed-optical timing synchronization scheme, the system can serve 15 remote optical and microwave sources in parallel via timing stabilized fiber links. Relative timing jitter between two link outputs is less than 1 fs RMS integrated over an extended measurement time from 1 μs to 2.5 days. The current system is also able to generate stabilized microwaves at the link outputs with 25-fs RMS precision over 8 h, which can be easily improved to few-femtosecond regime with higher quality VCOs.  
Using A Neural Network Control Policy For Rapid Switching Between Beam Parameters in an FEL  
  • A.L. Edelen, S. Biedron, S.V. Milton
    CSU, Fort Collins, Colorado, USA
  • P.J.M. van der Slot
    Mesa+, Enschede, The Netherlands
  FEL user facilities often must accommodate requests for a variety of beam parameters. This usually requires skilled operators to tune the machine, reducing the amount of available time for users. In principle, a neural network control policy that is trained on a broad range of operating states could be used to quickly switch between these requests without substantial need for human intervention. We present preliminary results from an ongoing study in which a neural network control policy is investigated for rapid switching between beam parameters in a compact THz FEL.  
MicroTCA.4 -Based Control for the Optical Synchronization System at the European XFEL  
  • M. Felber, E.P. Felber, M. Fenner, C. Gerth, M. Heuer, T. Kozak, T. Lamb, J.M. Müller, K.P. Przygoda, H. Schlarb, C. Sydlo, F. Zummack
    DESY, Hamburg, Germany
  The optical synchronization system at the European XFEL will serve as femtosecond-stable reference throughout the 3.5 km long facility. Its operation and performance is essential for the success of pump-probe experiments, first by enabling the LLRF system to stabilize the electron bunch arrival time and thereby the FEL X-ray pulse timing, and second by synchronizing the experimental laser with fs precision. The electronic hardware is realized in various MicroTCA.4 modules. Most of them are specially designed for this application but yet commercially available on the market due to licensing agreements between DESY and industry partners. In this paper we present the applied modules, the topology of the new systems and review the first operational experience.  
WEP034 Diagnostics Upgrades for Investigations of HOM Effects in TESLA-type SCRF Cavities 1
  • A.H. Lumpkin, N. Eddy, D.R. Edstrom, P.S. Prieto, J. Ruan, Y.-M. Shin, R.M. Thurman-Keup
    Fermilab, Batavia, Illinois, USA
  • B.E. Carlsten
    LANL, Los Alamos, New Mexico, USA
  Funding: Work at FNAL supported by Fermi Research Alliance, LLC under Contract No. DE-AC02-07CH11359 with the U.S. DoE. Work at LANL supported by U.S. DoE through the LANL/LDRD Program.
We describe the upgrades to diagnostic capabilities on the Fermilab Accelerator Science and Technology (FAST) electron linear accelerator that will allow investigations of the effects of high-order modes (HOMs) in SCRF cavities on macropulse-average beam quality. We focus here on the dipole modes in the first pass-band generally observed in the 1.6-1.9 GHz regime in TESLA-type SCRF cavities due to uniform transverse beam offsets of the electron beam. Such cavities are the basis of the accelerator for the European XFEL and the proposed MaRIE XFEL facility. Initial HOM data indicate that the mode intensities oscillate for about 10 microseconds after the micropulse enters the cavity, resulting in centroid shifts throughout the train. This results in a blurring of the averaged beam image size. The upgrades will include optimizing the HOM detectors' bandpass filters and adding a 1.3-GHz notch filter, converting the BPM electronics to bunch-by-bunch processing, and using the C5680 streak camera in a framing mode for bunch-by-bunch spatial information at the <20-micron level. The preliminary HOM detector data, prototype BPM test data, and first framing camera OTR data will be presented.
Adaptive Feedback for Automatic Phase-Space Tuning of Electron Beams in Advanced XFELs  
  • A. Scheinker
    LANL, Los Alamos, New Mexico, USA
  • D.K. Bohler
    SLAC, Menlo Park, California, USA
  Particle accelerators are extremely complex having thousands of coupled, nonlinear components which include magnets, laser sources, and radio frequency (RF) accelerating cavities. Many of these components are time-varying. One example is the RF systems which experience unpredictable temperature-based perturbations resulting in frequency and phase shifts. In order to provide users with their desired beam and thereby light properties, LCLS sometimes requires up to 6 hours of manual, experience-based hand tuning of parameters by operators and beam physicists, during a total of 12 hours of beam time provided for the user. Even standard operational changes can require hours to switch between user setups. The main goal of this work is to study model-independent feedback control approaches which can work together with physics-based controls to make overall machine performance more robust, enable faster tuning (seconds to minutes instead of hours), and optimize performance in real time in response to un-modeled time variation and disturbances.  
Sub-Micrometer Resolution, Nanotechnology Based Wire Scanners for Beam Profile Measurements at SwissFEL  
  • S. Borrelli, M. Bednarzik, Ch. David, E. Ferrari, A. Gobbo, V. Guzenko, N. Hiller, R. Ischebeck, G.L. Orlandi, C. Ozkan Loch, B. Rippstein, V. Schlott
    PSI, Villigen PSI, Switzerland
  SwissFEL Wire scanners (WSCs) measure electron beam transverse profile and emittance with high-resolution in a minimally-invasive way. They consist of a wire fork equipped with two 5 micrometer W wires, for high-resolution measurements, and two 12.5 micrometer Al(99):Si(1) wires, to measure the beam profile during FEL operation. Although the SwissFEL WSCs resolution is sufficient for many purposes, for some machine operations and experimental applications it is necessary to improve it under micrometer scale. The WSC spatial resolution is limited by the wire width which is constrained to few micrometers by the conventional manufacturing technique of stretching a metallic wire onto a wire-fork. In this work, we propose to overcome this limitation using the nanofabrication of sub-micrometer metallic stripes on a membrane by means of e-beam lithography. This presentation focuses in the design, construction and characterization of a high-resolution WSC prototype consisting of a silicon nitride membrane onto which two gold or nickel wires, widths ranging from 2 micrometers to 0.4 micrometers, are electroplated. We will also present the preliminary electron beam tests of our prototype.  
Saturation of Scintillators in Profile Monitors  
  • R. Ischebeck, E. Ferrari, F. Frei, N. Hiller, G.L. Orlandi, C. Ozkan Loch, V. Schlott
    PSI, Villigen PSI, Switzerland
  SwissFEL uses scintillating screens to measure the transverse profile of the electron beam. These screens, in combination with quadrupole magnets and a transverse deflecting RF structure, are used to measure projected and slice emittance, as well as bunch length. Scintillating screens have been chosen over optical transition radiators because of the coherent transition radiation emitted by the compressed bunches. It is therefore instrumental to characterize the linearity of these monitors in order to ensure reliable measurements. We are presenting here a measurement of saturation effects due to the high charge density in SwissFEL, and describe the results with a numerical model of the process.  
WEP040 Sub-Femtosecond Time-Resolved Measurements Based on a Variable Polarization X-Band Transverse Deflecting Structures for SwissFEL 1
  • P. Craievich, M. Bopp, H.-H. Braun, R. Ganter, M. Pedrozzi, E. Prat, S. Reiche, R. Zennaro
    PSI, Villigen PSI, Switzerland
  • R.W. Aßmann, F. Christie, R.T.P. D'Arcy, B. Marchetti, D. Marx
    DESY, Hamburg, Germany
  • N. Catalán Lasheras, A. Grudiev, G. McMonagle, W. Wuensch
    CERN, Geneva, Switzerland
  The SwissFEL project, under commissioning at the Paul Scherrer Institut (PSI), will produce FEL radiation for soft and hard X-rays with pulse durations ranging from a few to several tens of femtoseconds. A collaboration between DESY, PSI and CERN has been established with the aim of developing and building an advanced X-Band transverse deflector structure (TDS) with the new feature of providing variable polarization of the deflecting force. As this innovative CERN design requires very high manufacturing precision to guarantee highest azimuthal symmetry of the structure to avoid the deterioration of the polarization of the streaking field, the high-precision tuning-free assembly procedures developed at PSI for the SwissFEL C-band accelerating structures will be used for the manufacturing. Such a TDS will be installed downstream of the undulators of the soft X-ray beamline of SwissFEL and thanks to the variable polarization of the TDS, it will be possible to perform a complete characterization of the 6D phase-space. We summarize in this work the status of the project and its main technical parameters.  
WEP041 HLS to Measure Changes in Real Time in the Ground and Building Floor of PAL-XFEL, Large-Scale Scientific Equipment 1
  • H. J. Choi, J.H. Han, H.-S. Kang, S.H. Kim, H.-G. Lee, S.B. Lee
    PAL, Pohang, Kyungbuk, Republic of Korea
  A variety of parts that comprise large-scale scientific equipment should be installed and operated at accurate three-dimensional location coordinates (X, Y, Z) through survey and alignment in order to ensure optimal performance. However, uplift or subsidence of the ground occurs over time, and consequently causes the deformation of building floors. The deformation of the ground and buildings cause changes in the location of installed parts, eventually leading to alignment errors (ΔX, ΔY, ΔZ) of components. As a result, the parameters of the system change and the performance of large-scale scientific equipment is degraded. Alignment errors that result from changes in building floor height can be predicted by real-time measurement of changes in building floors. This produces the advantage of reducing survey and alignment time by selecting the region where great changes in building floor height are shown and re-aligning components in the region in a short time. To do so, HLS (hydrostatic leveling sensor) with a resolution of 0.2 micrometers and a waterpipe of 1 km are installed at the PAL-XFEL building. This paper introduces the installation and operation status of HLS.  
poster icon Poster WEP041 [0.827 MB]  
WEP043 Tune-Up Simulations for LCLS-II 1
  • M.W. Guetg, P. Emma
    SLAC, Menlo Park, California, USA
  The planned superconducting LCLS-II linac poses new operational constraints with respect to the existing copper linac currently operated for LCLS. We present the results of exhaustive accelerator simulations, including realistic machine errors and exploring beam tune-up strategies. The results are used to pin-point the required beam diagnostics and the key correction elements. Specifically, these simulations concentrate on longitudinal and transverse beam matching as well as orbit and dispersion control through the new linac and up to the hard x-ray FEL. Dispersion control is achieved by a novel method presented within this paper.  
WEP044 Beam Loss Monitor for Undulators in PAL-XFEL 1
  • H. Yang, D.C. Shin
    PAL, Pohang, Kyungbuk, Republic of Korea
  Funding: This work is supported by MSIP, Korea.
PAL-XFEL consists of the hard x-ray line with a 4-10 GeV electron beam and the soft x-ray line with a 3-3.5 GeV electron beam. The HX line consists of 20 undulators and the SX line consists of 7 undulators. The permanent magnets in an undulator should be protected from the radiation-induced demagnetization. We develop a beam loss monitor (BLM) for undulators of PAL-XFEL. It consists of a detector part (head) and an ADC part. The BLM head consists of two fused quartz rods, two photo-multiplier tube (PMT) modules, and an LED bulb. It is based on the Cherenkov radiator: two fused quartz rods are used for radiators. 2 sets of the radiator and PMT module are installed up and down the beam tube. An LED bulb is between the radiators for the heartbeat signal. The ADC part digitizes the output signal of the PMT module. It measures and calculates the beam loss, background, and heartbeat. One ADC processes the signal from 6-8 heads. The BLM system generates interlock to the machine interlock system for over-threshold beam loss. The 28 BLM heads are installed downstream of each undulator. Those are calibrated by the heartbeat signal and operated in the electron beam transmission with 150 pC.
poster icon Poster WEP044 [1.770 MB]  
Transition Radiation Beam Profile Diagnostics at EUV Wavelengths  
  • A.Y. Murokh, M. Ruelas, H.L. To
    RadiaBeam, Santa Monica, California, USA
  We propose a method of measuring transverse profile of high quality photo-injector generated electron beams, using a backscattered transition radiation from multilayer mirrors at the extreme ultraviolet (EUV) spectral region. The motivation for such a short wavelength is twofold: to mitigate coherent effects (COTR) detrimental to beam profile measurements at longer wavelengths; and to achieve sub-micron resolution for high precision applications such as those requiring electron beam matching into photonic structures. The specific wavelength of 13.5 nm was selected to take advantage of high quality optics availability. We discuss anticipated EUV TR signal amplitude and detection methods, analyze strengths and challenges of the proposed system in comparison with more conventional diagnostic methods, and provide a status report on the prototype system development and planned installation and testing at LCLS.