FEL2017 - Classification: Electron Diagnostics, Timing, Controls

Paper	Title	Page
WEB01	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.
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WEB02	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.
	Slides WEB02 [13.820 MB]
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WEB03	R&D at SLAC on Nanosecond-Range Multi-MW Systems for Advanced FEL Facilities	404
	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 WEB03 [6.521 MB]
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-FEL2017-WEB03
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WEB04	Laser-to-RF Synchronization with Femtosecond Precision	407
	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 WEB04 [5.683 MB]
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-FEL2017-WEB04
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WEB05	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.
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WEP027	Numerical Study of Cherenkov Radiation From Thin Silica Aerogel	479
	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.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-FEL2017-WEP027
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WEP029	Recent Experimental Results on High-Peak-Current Electron Bunch and Bunch Trains Interacting With a THz Undulator	482
	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
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-FEL2017-WEP029
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WEP030	Large-Scale Turnkey Timing Distribution System for New Generation Photon Science Facilities	485
	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.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-FEL2017-WEP030
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WEP031	Using A Neural Network Control Policy For Rapid Switching Between Beam Parameters in an FEL	488
	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.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-FEL2017-WEP031
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WEP034	Diagnostics Upgrades for Investigations of HOM Effects in TESLA-type SCRF Cavities	492
	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.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-FEL2017-WEP034
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WEP036	Adaptive Feedback for Automatic Phase-Space Tuning of Electron Beams in Advanced XFELs	496
	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.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-FEL2017-WEP036
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WEP040	Sub-Femtosecond Time-Resolved Measurements Based on a Variable Polarization X-Band Transverse Deflecting Structures for SwissFEL	499
	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.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-FEL2017-WEP040
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WEP041	HLS to Measure Changes in Real Time in the Ground and Building Floor of PAL-XFEL, Large-Scale Scientific Equipment	503
	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 WEP041 [0.832 MB]
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-FEL2017-WEP041
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WEP043	Tune-Up Simulations for LCLS-II	507
	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.
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WEP044	Beam Loss Monitor for Undulators in PAL-XFEL	511
	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 WEP044 [1.775 MB]
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-FEL2017-WEP044
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Paper

Title

Page

WEB01

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.

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WEB02

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.

Slides WEB02 [13.820 MB]

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WEB03

R&D at SLAC on Nanosecond-Range Multi-MW Systems for Advanced FEL Facilities

404

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 WEB03 [6.521 MB]

DOI •

reference for this paper ※ https://doi.org/10.18429/JACoW-FEL2017-WEB03

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WEB04

Laser-to-RF Synchronization with Femtosecond Precision

407

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 WEB04 [5.683 MB]

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reference for this paper ※ https://doi.org/10.18429/JACoW-FEL2017-WEB04

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WEB05

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.

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WEP027

Numerical Study of Cherenkov Radiation From Thin Silica Aerogel

479

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.

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WEP029

Recent Experimental Results on High-Peak-Current Electron Bunch and Bunch Trains Interacting With a THz Undulator

482

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

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WEP030

Large-Scale Turnkey Timing Distribution System for New Generation Photon Science Facilities

485

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.

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WEP031

Using A Neural Network Control Policy For Rapid Switching Between Beam Parameters in an FEL

488

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.

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WEP034

Diagnostics Upgrades for Investigations of HOM Effects in TESLA-type SCRF Cavities

492

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.

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WEP036

Adaptive Feedback for Automatic Phase-Space Tuning of Electron Beams in Advanced XFELs

496

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.

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WEP040

Sub-Femtosecond Time-Resolved Measurements Based on a Variable Polarization X-Band Transverse Deflecting Structures for SwissFEL

499

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.

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WEP041

HLS to Measure Changes in Real Time in the Ground and Building Floor of PAL-XFEL, Large-Scale Scientific Equipment

503

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 WEP041 [0.832 MB]

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WEP043

Tune-Up Simulations for LCLS-II

507

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.

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WEP044

Beam Loss Monitor for Undulators in PAL-XFEL

511

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 WEP044 [1.775 MB]

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