WEP —  Poster III   (23-Aug-17   15:30—17:30)
Paper Title Page
The Photoinjector and Seed Laser Systems of DCLS  
  • G.R. Wu, D.X. Dai, G.L. Wang, X.M. Yang, W.Q. Zhang
    DICP, Dalian, People's Republic of China
  DCLS is free electron laser user facility based on HGHG concept. Two ultrafast laser systems are involved: the photoinjector laser system (PIL) and seed laser system (SL). Both laser systems have been installed and taken part in the commissioning of DCLS since September, 2016. Both laser systems are based on an all-CW-diode-pumped Ti:Sapphire amplifier system. PIL includes a delay-line type third harmonic generation scheme, a direct 3D shaping setup, and an imaging-relay transportation system. SL has two operation modes: 1 ps and 100 fs. It can be switched between these two modes. For the 100 fs mode, a delay-line based THG box is installed which delivers either 400 or 267 nm laser pulse as the seed. As for the 1 ps mode, a ps-OPA is used to deliver seed laser pulse with a wavelength between 240 and 360 nm. In this paper, we report the detailed design and the current status of these two laser systems.  
Double Pulse FEL Operation at FLASH  
  • S. Schreiber, K. Klose
    DESY, Hamburg, Germany
  The free-electron laser facility FLASH at DESY (Hamburg, Germany) has been a user facility since 2005 providing high-brilliance XUV and soft X-ray pulses. The facility runs 10-Hz bursts of hundreds of electron bunches, where the bunch distance in the burst is 1 microsecond or more. Some experiments ask for operation modes, with bunches as close as a few ps, ns or hundreds of ns. We report on operation of FLASH with these kind of double pulses for experiments using double soft X-rays and/or THz radiation pulses.  
poster icon Poster WEP002 [0.330 MB]  
WEP003 Update on the Lifetime of Cs2Te Photocathodes Operated at FLASH 1
  • S. Schreiber, S. Lederer
    DESY, Hamburg, Germany
  • P. Michelato, L. Monaco, D. Sertore
    INFN/LASA, Segrate (MI), Italy
  The photoinjector of the free-electron laser facility FLASH at DESY (Hamburg, Germany) uses Cs2Te photocathodes. We report on an update of the lifetime and quantum efficiency of cathodes operated at FLASH during the last years.  
poster icon Poster WEP003 [0.281 MB]  
WEP004 Calculations for a THz SASE FEL Based on the Measured Electron Beam Parameters at PITZ 1
  • P. Boonpornprasert, M. Krasilnikovpresenter, F. Stephan
    DESY Zeuthen, Zeuthen, Germany
  The Photo Injector Test facility at DESY, Zeuthen site (PITZ), develops high brightness electron sources for modern linac-based Free Electron Lasers (FELs). The PITZ accelerator can also be considered as a suitable machine for the development of an IR/THz source prototype for pump-probe experiments at the European XFEL. Calculations of THz radiation by means of a SASE FEL based on the simulated and the measured beam profiles at PITZ for the radiation wavelength of 100 microns were performed by using the GENESIS1.3 code. The results of these simulations are presented and discussed in this paper.  
WEP005 Coaxial Coupler RF Kick in the PITZ RF Gun 1
  • Y. Chen, P. Boonpornprasert, J.D. Good, H. Huck, I.I. Isaev, M. Krasilnikovpresenter, A. Oppelt, H.J. Qian, Y. Renier, F. Stephan
    DESY Zeuthen, Zeuthen, Germany
  • W. Ackermann, H. De Gersem
    TEMF, TU Darmstadt, Darmstadt, Germany
  • M. Dohlus
    DESY, Hamburg, Germany
  • Q.T. Zhao
    IMP/CAS, Lanzhou, People's Republic of China
  We investigate a transverse RF kick induced by the transition between rectangular waveguide and coaxial line of the RF coupler in the 1.6-cell L-band normal conducting (NC) RF gun at the Photo Injector Test Facility at DESY, Zeuthen site (PITZ). A three-dimensional electromagnetic simulation shows the disturbed RF field distributions in the fundamental accelerating mode. Based on the 3D RF field map, an electron beam based characterization and quantification of the coaxial coupler RF kick in the PITZ gun is simulated. Preliminary results of the investigations are presented.  
poster icon Poster WEP005 [1.340 MB]  
WEP006 Preliminary On-Table and Photoelectron Results from the PITZ Quasi-Ellipsoidal Photocathode Laser System 1
  • J.D. Good, G. Asova, P. Boonpornprasert, Y. Chen, M. Groß, H. Huck, I.I. Isaev, D.K. Kalantaryan, M. Krasilnikov, X. Li, O. Lishilin, G. Loisch, D. Melkumyan, A. Oppelt, H.J. Qian, Y. Renier, T. Rublack, F. Stephan
    DESY Zeuthen, Zeuthen, Germany
  • A.V. Andrianov, E. Gacheva, E. Khazanov, S. Mironov, A. Poteomkin, V. Zelenogorsky
    IAP/RAS, Nizhny Novgorod, Russia
  • I. Hartl, S. Schreiber
    DESY, Hamburg, Germany
  • E. Syresin
    JINR, Dubna, Moscow Region, Russia
  The optimization of photoinjectors is crucial for the successful operation of linac-based free electron lasers, and beam dynamics simulations have shown that ellipsoidal photocathode laser pulses result in significantly lower electron beam emittance than that of conventional cylindrical pulses. Therefore, in collaboration with the Institute of Applied Physics (Nizhny Novgorod, Russia) and the Joint Institute of Nuclear Research (Dubna, Russia), a laser system capable of generating quasi-ellipsoidal laser pulses has been developed and installed at the Photo Injector Test facility at DESY, Zeuthen site (PITZ). The pulse shaping has been realized using the spatial light modulator technique, characterized by cross-correlation and spectrographic measurements, and is demonstrated with electron beam measurements. In this contribution the overall setup, operating principles, and results of first regular electron beam measurements will be presented together with corresponding beam dynamics simulations. Furthermore, the numerous improvements of the simplified re-design currently under construction shall be detailed.  
poster icon Poster WEP006 [1.761 MB]  
WEP007 Electron Beam Asymmetry Compensation with Gun Quadrupoles at PITZ 1
  • M. Krasilnikov, P. Boonpornprasert, Y. Chen, J.D. Good, M. Groß, H. Huck, I.I. Isaev, D.K. Kalantaryan, X. Li, O. Lishilin, G. Loisch, D. Melkumyan, A. Oppelt, H.J. Qian, Y. Renier, F. Stephan, Q.T. Zhao
    DESY Zeuthen, Zeuthen, Germany
  • G.A. Amatuni, B. Grigoryan
    CANDLE SRI, Yerevan, Armenia
  • G. Asova
    INRNE, Sofia, Bulgaria
  • Q.T. Zhao
    IMP/CAS, Lanzhou, People's Republic of China
  The electron beam asymmetry observed at the Photo Injector Test Facility at DESY in Zeuthen (PITZ) was traced back to multipole kicks in the gun section, namely around the location of the coaxial power coupler and the main solenoid. Several dedicated studies have been performed to quantify the kick location and strength. Based on these studies, two designs of correction quadrupole coils were proposed. The coils were fabricated and tested with an electron beam. The second updated design implies a two quadrupole setup on a frame installed around the gun coaxial coupler close to the main solenoid centre location. Skew and normal quadrupole magnets are powered independently, enabling flexibility in electron beam manipulations. By means of this setup, a more symmetric beam was obtained at several screens. This led also to more equal measured horizontal and vertical phase spaces and to even smaller overall emittance values. Some details of the gun quadrupole designs, magnetic measurements, and results of electron beam measurements including emittance optimization will be reported.  
poster icon Poster WEP007 [1.992 MB]  
WEP008 Beam Brightness Improvement by Ellipsoidal Laser Shaping for CW Photoinjectors 1
  • H.J. Qian, M. Krasilnikov, F. Stephanpresenter
    DESY Zeuthen, Zeuthen, Germany
  High-brightness photoinjectors operating in a continuous wave (CW) mode are required for many advanced applications, such as CW X-ray FEL, ERL light source, electron coolers for hadron beams and electron-ion colliders and so on. Now, three types of CW electron guns are available: DC gun, SRF gun and normal conducting RF gun, which are under intense development in different institutes based on local expertise and application demands. Compared to pulsed guns, both beam energy and brightness from CW guns are compromised due to a lower acceleration gradient. Flattop laser shaping has been applied in both pulsed and CW guns to improve beam emittance. In this paper, ellipsoidal laser shaping is applied in CW photoinjectors to improve beam brightness, and preliminary ASTRA simulations are presented.  
WEP009 A Cryocooled Normal-Conducting and Superconducting Hybrid CW Photoinjector 1
  • H.J. Qian, M. Krasilnikov, F. Stephanpresenter
    DESY Zeuthen, Zeuthen, Germany
  Continuous wave (CW) photoinjectors have seen great progress in the last decades, such as DC gun, SRF gun and normal conducting VHF-band RF gun. New developments of CW guns are aiming higher acceleration gradient and beam energy for higher-beam brightness. One of the technical challenges for CW SRF guns is the compatibility of normal-conducting high QE cathodes and superconducting cavity. In this paper, a high gradient cryocooled CW normal-conducting gun is proposed to house the high QE cathode, and a SRF cavity nearby gives further energy acceleration. Preliminary ASTRA simulations of such a hybrid photoinjector are presented.  
WEP010 Beam Asymmetry Studies with Quadrupole Field Errors in the PITZ Gun Section 1
  • Q.T. Zhao, G. Asova, P. Boonpornprasert, Y. Chen, J.D. Good, M. Groß, H. Huck, I.I. Isaev, D.K. Kalantaryan, M. Krasilnikovpresenter, X. Li, O. Lishilin, G. Loisch, D. Melkumyan, A. Oppelt, H.J. Qian, Y. Renier, T. Rublack, C. Saisa-ard, F. Stephan
    DESY Zeuthen, Zeuthen, Germany
  • G. Asova
    INRNE, Sofia, Bulgaria
  • C. Saisa-ard
    Chiang Mai University, Chiang Mai, Thailand
  • Q.T. Zhao
    IMP/CAS, Lanzhou, People's Republic of China
  The Photo Injector Test Facility at DESY in Zeuthen (PITZ) was built to test and optimize high-brightness electron sources for free electron lasers (FELs) like FLASH and European XFEL. Although the beam emittance has been optimized and experimentally demonstrated to meet the requirements of FLASH and XFEL, transverse beam asymmetries, such as wing structures and beam tilts, were observed during many years of operation with different generations of guns. These cannot be explained by simulations with the rotationally symmetric gun cavities and symmetric solenoid fields. Based on previous RF coupler kick, solenoid field imperfection studies and coupling beam dynamics, the beam asymmetries most probably stem from rotated quadrupole field error in the gun section. A thin-lens static quadrupole model is applied in the RF gun section simulations to fit the position and intensity of quadrupole field errors by comparing the beam asymmetry directions in experiments and ASTRA simulations. Furthermore, by measuring the laser position movement at the photo cathode and the corresponding beam movement at downstream screens, the integrated quadrupole field strength can also be extracted.  
poster icon Poster WEP010 [1.852 MB]  
WEP012 A 2.45 GHz Photoinjector Gun for an FEL Driven by Laser Wakefield Accelerated Beam 1
  • S.V. Kuzikov, S.A. Bogdanov, E. Gacheva, E.V. Ilyakov, D.S. Makarov, S. Mironov, A. Poteomkin, A. Shkaev, A.A. Vikharev
    IAP/RAS, Nizhny Novgorod, Russia
  Funding: This work was supported by the Russian Scientific Foundation (grant #16-19-10448).
The photoinjector of short electron bunches is a key element of investigations aimed on particle acceleration by pulses of the subpetawatt laser PEARL (10 J, 50-70 fs). The projected parameters of the photoinjector are an electron energy level of 5 MeV, a charge > 0.1 nC, a bunch length of about 3 mm, a transversal emittance no worse than 1 mm*mrad, and an energy spread no more than ~0.1%. The photoinjector is based on klystron KIU-111 at frequency 2.45 GHz, produced by company Toriy (output power ~ 5 MW, pulse length ~ 7 mcs, efficiency ~ 44%, power gain ~ 50 dB). It is proposed to use this klystron in order to feed the accelerating resonator of the classical design consisted of 1.5 cells in which the photocathode is inserted. On a base of third harmonics of a Ti:Sa laser, we plan to produce picosecond pulses of no less than 100 mcJ in energy. The photocathode is planned to be made of CVD diamond film which is not critical to vacuum degree and surface contamination, has high QE, a long lifetime, and is capable of being used with cheap, long wavelength optical lasers.
poster icon Poster WEP012 [1.190 MB]  
Photocathode RF Gun Development at KAERI for Time-Resolving Pump/Prove System  
  • K.H. Jang, Y.U. Jeong, H.W. Kim
    KAERI, Daejon, Republic of Korea
  • J.H. Han
    PAL, Pohang, Kyungbuk, Republic of Korea
  • N.A. Vinokurov
    BINP SB RAS, Novosibirsk, Russia
  A photocathode RF gun-based pump/prove system has been developed at KAERI. The facility is mainly composed of a 1.6 cell S-band RF gun, a travelling wave-type linac and 90 degree achromatic magnetic-bends. Actually, it has four beam lines. The front two beam lines of the facility are designed for time-resolving UV & THz pump/electron beam prove experiments, and the last two beam lines are for THz pump/X-ray prove experiments. The photocathode RF gun installed in the system was designed to have a coaxial cylindrical coupler to be able to operate at high repetition rate by emitting the heat quickly with symmetrically water-cooling channels surrounding the RF cavity, and also to position gun solenoid at an optimum location. In the conference, we will present not only the design and fabrication of the gun itself but also the electron emission test results.  
WEP014 Pulse Duration Measurement of Pico-second DUV Photocathode Driving Laser by Autocorrelation Technique Using Two-Photon Absorption in Bulk Material 1
  • H. Zen, T. Kii, K. Masuda, T. Nakajima, H. Ohgaki
    Kyoto University, Kyoto, Japan
  A multi-bunch, pico-second DUV photocathode drive laser system has been developed for photocathode operation of mid-infrared free electron laser facility, KU-FEL.* By using the laser, KU-FEL has already succeeded in first lasing under the photocathode operation.** The pulse duration of the photocathode driving laser is a quite important parameter because it determines the initial electron pulse duration on the cathode surface. However, the pulse duration of the photocathode driving laser had not been characterized. A very convenient pulse duration measurement method utilizing two-photon absorption in bulk material, which can be used for DUV laser pulses, has been proposed and demonstrated so far.*** In this study, a DUV nonlinear autocorrelator based on the proposed method was developed to measure the pulse duration of the DUV photocathode driving laser. As the result of measurement, the pulse duration was evaluated as 5.8±0.2 ps (FWHM). The principle of this method, experimental setup and measured results will be presented.
* H. Zen et al., Proc. of FEL2014, pp.828-831 (2015).
** H. Zen et al., Proc. of IPAC2016, pp.754-756 (2016).
*** C. Homann et al., Applied Physics B 104, 783 (2011).
WEP015 Current Experimental Work with Diamond Field-Emitter Array Cathodes 1
  • H.L. Andrews, R.L. Fleming, J.W. Lewellen, K.E. Nichols, D.Y. Shchegolkov, E.I. Simakov
    LANL, Los Alamos, New Mexico, USA
  • B.K. Choi
    Vanderbilt University, Nashville, USA
  Funding: We gratefully acknowledge the support of the U.S. Department of Energy through the LANL/LDRD Program for this work.
Diamond Field-Emitter Array (DFEA) cathodes are arrays of micron-scale diamond pyramids with nanometer-scale tips, thereby providing high emission currents with small emittance and energy spread. To date they have been demonstrated in a close-diode configuration, spaced only a few hundred microns from a solid anode, and have shown very promising results in terms of emittance, energy spread, and per-tip emission currents. We present recent results investigating DFEA performance in a large-gap configuration, such that the cathodes are a few millimeters from a solid anode, and show that performance is the same or better as the close-diode geometry previously studied. However, array performance is still limited by anode damage. We are redesigning our cathode test stand to overcome the inherent limitations of a solid anode, allow for transport of the emitted beam, and further explore real-world DFEA performance.
WEP016 Modeling of Diamond Field-Emitter Arrays for High-Brightness Photocathode Applications 1
  • C. Huang, H.L. Andrews, B.K. Choi, R.L. Fleming, T.J. Kwan, J.W. Lewellen, D.C. Nguyen, K.E. Nichols, V.N. Pavlenko, A. Piryatinski, D.Y. Shchegolkov, E.I. Simakov
    LANL, Los Alamos, New Mexico, USA
  Funding: Work performed under the auspices of the U.S. DOE by the LANS, LLC, Los Alamos National Laboratory (LANL) under Contract No. DE-AC52-06NA25396. Work supported by the LDRD program at LANL.
Dielectric Laser Accelerator (DLA) is capable of generating high output power for an X-ray free-electron laser (FEL), while having a size 1-2 orders of magnitude smaller than existing Radio-Frequency (RF) accelerators. Single Diamond Field-Emitter (DFE) or array of such emitters (DFEA) can be employed as high-current ultra-low-emittance photocathodes for compact DLAs. We are developing a first principle semi-classical Monte-Carlo (MC) emission model for DFEAs that includes the effects of carriers' photoexcitation, their transport to the emitter surface, and the tunnelling through the surface. The electronic structure size quantization affecting the transport and tunnelling processes within the sharp diamond tips is also accounted for. These aspects of our model and their implementation and validation, as well as macroscopic electromagnetic beam simulation of DFE are discussed.
The Multiphysics Photocathode Growth and Characterization System at LANL  
  • M.A. Hoffbauer, J.W. Lewellen, N.A. Moody, V.N. Pavlenkopresenter
    LANL, Los Alamos, New Mexico, USA
  Funding: We gratefully acknowledge the support of the U.S. Department of Energy through the LANL/LDRD Program for this work.
A versatile multiphysics photocathode growth and characterization system is being commissioned by the Applied Cathode Enhancement and Robustness Technology (ACERT) team at LANL. The multiphysics system brings together state-of-the-art surface-science capabilities and leverages unique LANL capabilities to provide an integrated system consisting of (i) bi-alkali antimonide and nitride semiconductor thin-film growth, (ii) advanced surface-science characterization tools, and (iii) incorporation of photocathodes into an operational electron-gun cathode assembly for quantitative beam emittance measurements. Our goal is to provide a modular integrated UHV platform for advancing photocathode performance to the levels needed for the next generation of advanced FELs and accelerators.
WEP018 Electron Beam Heating with the European XFEL Laser Heater 1
  • M. Hamberg
    Uppsala University, Uppsala, Sweden
  • F. Brinker, I. Hartl, S. Koehler, B. Manschwetus, M. Scholz, L. Winkelmann
    DESY, Hamburg, Germany
  Funding: Work supported by Swedish Research council, Sweden, Olle Engkvist foundation and DESY, Hamburg, Germany.
The commissioning of the European XFEL is ongoing. To reduce unwanted longitudinal micro-bunching effects, a laser heater is implemented. Here we present the first heating steps and commissioning of the laser heater at the injector section.
High Stable Pulse Modulator for PAL-XFEL*  
  • S.S. Park, H.-S. Kang, S.H. Kim, H.-S. Lee
    PAL, Pohang, Kyungbuk, Republic of Korea
  Funding: Work supported by Ministry of Science, ICT(Information/Communication Technology) and Future Planning.
The XFEL of Pohang Accelerator Laboratory (PAL) commissioned the 10 GeV PAL-XFEL project in 2015. The PAL-XFEL needs a highly-stable electron beam. The very stable beam voltage of a klystron-modulator is essential to provide the stable acceleration field for an electron beam. Thus, the modulator system for the XFEL requires less than 50 ppm PFN voltage stability. To get this high stability on the modulator system, the HVPS of inverter type is an important component. The modulator also needs lower noise and more smart. In this paper, we will discuss the design and the test results of the high-stability pulse modulator system.
Longitudinal Shaping of the Max IV Photocathode Gun Laser Pulses  
  • M. Kotur, J. Andersson, F. Curbis, F. Lindau, S. Thorin, S. Werin
    MAX IV Laboratory, Lund University, Lund, Sweden
  The longitudinal shape of the driver laser pulse plays an important role in producing a low-emittance beam in a photocathode electron gun. Here we present a Fourier-domain pulse shaping setup, which is being developed with the goal of being able to achieve arbitrary shapes of the UV laser pulse. Comparisons of the preliminary results with the standard pulse stacking scheme are discussed.  
Preliminary Results of the Dark Current Modelling for the Polfel Superconducting Lead Photocathode  
  • K. Szymczyk, J.A. Lorkiewiczpresenter, R. Nietubyć
    NCBJ, Świerk/Otwock, Poland
  • J.K. Sekutowicz
    DESY, Hamburg, Germany
  Preparation for the construction of Polish Free Electron Laser (POLFEL) will begin shortly at National Centre for Nuclear Research (NCBJ) in Warsaw. POLFEL is planned as a fourth-generation light source driven by a superconducting (sc) electron accelerator. The concept includes an all-superconducting injector with a thin-film lead sc photocathode, dedicated to continuous wave or long-pulse linac operation. One of the issues which emerges in connection with operation of high-gradient electron guns furnished with dismountable photocathode plugs is the dark current emitted from the cathode surface inhomogeneities. The dark current usually degrades accelerator performance. The purpose of this paper is to present preliminary investigation results of the dark current generation in the electron gun with a thin lead layer deposited on a niobium plug. Specific features of geometric configuration like rounded plug edges, a gap between the plug and the back gun wall as well as cathode surface roughness have been taken into account for the electron field emission and RF field calculations.  
Commissioning of the SwissFEL Linac  
  • F. Löhl
    PSI, Villigen PSI, Switzerland
  Since summer 2016, the C-band linear accelerator of SwissFEL has been progressively commissioned. This paper will summarize the first commissioning experience of the first C-band modules and will give an outlook for the planned activities for the remainder of this year.  
WEP024 Design and Research of a Micro-Pulse Electron Gun 1
  • D.Y. Yang, B.T. Li, X.Y. Lu, W.W. Tan, L. Xiao, Y. Yang, Z.Q. Yang, J. Zhao
    PKU, Beijing, People's Republic of China
  • K. Zhou
    CAEP/IAE, Mianyang, Sichuan, People's Republic of China
  Micro-pulse electron gun (MPG) is a novel electron source which can produce narrow-pulse, high-repetition rate electron current. Theoretical and experiment work have been done to study physical properties and steady operating conditions of MPG. Proof-of-principle work has been finished and the next work is to research the parameters of the MPG electron beam and master the MPG work property deeply. Thus, a high voltage accelerating platform which can supply 100 kV direct voltage was designed. Furthermore, electromagnetic and mechanism designs were operated to adapt the high voltage platform and measure beam parameters.  
Emittance Measurements from SRF Gun in CeC Accelerator  
  • K. Mihara
    Stony Brook University, Stony Brook, USA
  • Y.C. Jing, V. Litvinenko, I. Pinayev, G. Wang
    BNL, Upton, Long Island, New York, USA
  • I. Petrushina
    SUNY SB, Stony Brook, New York, USA
  Funding: DoE NP office, grant DE-FOA-0000632 and NSF grant PHY-1415252
In this paper we report on extremely good performance of 113 MHz SRF CW gun. This gun is a part of the system built to test coherent electron cooling concept and was aimed to generate trains of 78 kHz pulses with large 1 nC to 5 nC charge per bunch. While it was not built for attaining record low emittances, the machine can achieve very low normalized emittances ~ 0.3 mm mrad with 0.5 nC charge per bunch using CsK2Sb photocathode. In addition to excellent performance, this gun provides for very long lifetime of these high QE photocathodes, with a typical using time of 2 months.
WEP026 Inducing Microbunching in the CLARA FEL Test Facility 1
  • A.D. Brynes
    STFC/DL/ASTeC, Daresbury, Warrington, Cheshire, United Kingdom
  We present simulation studies of the laser heater interaction in the CLARA FEL test facility using a non-uniform laser pulse. The microbunching instability, which manifests itself as correlated energy or density modulations in an electron bunch, can degrade the performance of an FEL. Most x-ray free electron lasers (FELs) utilise a so-called laser heater system to impose a small increase in the uncorrelated energy spread of the bunch at low energy to damp the instability – this technique involves imposing a laser pulse on the bunch while it is propagating through an undulator in a dispersive region. However, if the instability can be controlled, the electron bunch profile can be manipulated, yielding novel applications for the FEL, or for generation of THz radiation. Control of the microbunching instability can be achieved by modulating the intensity profile of the laser heater pulse to impose a non-uniform kick along the electron bunch. We have simulated this interaction for various laser intensity profiles and bunch compression factors.  
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. Yanpresenter
    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. Ischebeckpresenter, 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. Pratpresenter, 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. Kangpresenter, 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.  
WEP048 Coherent Undulator Radiation From a Kicked Electron Beam 1
  • J.P. MacArthur, Z. Huang, J. Krzywinski, A.A. Lutman
    SLAC, Menlo Park, California, USA
  The properties of off-axis radiation from an electron beam that has been kicked off axis are relevant to recent Delta undualtor experiments at LCLS. We calculate the coherent emission from a microbunched beam in the far-field, and compare with simulation. We also present a mechanism for microbunches to tilt toward a new direction of propagation.  
Stimulated Emission/Absorption of Radiation by a Single Electron Quantum Wavepacket  
  • A. Gover, Y. Panpresenter
    University of Tel-Aviv, Faculty of Engineering, Tel-Aviv, Israel
  Funding: Partial support by Deutsche-Israelische Projektkooperation (DIP) and US-Israel Binational Science Foundation (BSF).
We analyze the stimulated (emission/absorption) interaction of a single electron quantum wavepacket with coherent radiation, using perturbation theory and numerical solution. The analysis applies to a wide class of free electron radiative-interaction schemes, and is exemplified for Smith-Purcell radiation. Contrary to spontaneous emission, stimulated radiative interaction depends on the wavepacket characteristics in a certain quantum range. If the electron drifts beyond a critical length, then dimension-dependent acceleration of the wavepacket is fundamentally impossible because of the wavepacket spread. Below this range, such acceleration is possible, approaching the limit of classical 'point particle' linear acceleration, at the conditions of small wavepacket dimensions relative to the radiation wavelength and multi-photon exchange. Our analysis emulates the FEL gain in the limit of negligible recoil, and the quantum momentum recoil sidebands characteristics of PINEM - when recoil effect is significant. We use the platform for discussing the fundamental physics question of measurability of the quantum wavepacket size and the limitation of the classical 'white' shot-noise model.
WEP051 Helical Undulators for Coherent Electron Cooling System 1
  • I. Pinayev, Y.C. Jing, R. Kellermann, V. Litvinenko, J. Skaritka, G. Wang
    BNL, Upton, Long Island, New York, USA
  • I.V. Ilyin, Y. Kolokolnikov, P. Vobly
    BINP SB RAS, Novosibirsk, Russia
  Funding: DoE NP office, grant DE-FOA-0000632
In this paper we present the description and results of the magnetic measurements and tuning of helical undulators for the Coherent electron Cooling system (CeC). The FEL section of the CeC comprises three 2.5-m long undulators separated by 40-cm drift sections, where BPMs and phase-adjusting 3-pole wigglers are located. We present design, tuning techniques and achieved parameters of this system.
Study of a Superconducting THz Undulator at the European XFEL  
  • T. Tanikawa, G. Geloni, S. Karabekyan
    XFEL. EU, Schenefeld, Germany
  • V. B. Asgekar, M. Gensch
    HZDR, Dresden, Germany
  • S. Casalbuoni
    KIT, Eggenstein-Leopoldshafen, Germany
  The European XFEL has successfully achieved a first lasing in May 2017. Meanwhile, a THz radiation for pump-probe experiments etc. is under consideration at the European XFEL using laser-based and/or accelerator-based techniques. A superconducting THz undulator as an afterburner is one option, but a challenge to this approach is the usage of very high electron-beam energy up to 17.5 GeV and the requirement of a high magnetic field. In this presentation, we will report the preliminary study of the THz undulator design and the radiation properties at the European XFEL.  
WEP054 The Magnetic Field Integral Hysteresis on the European XFEL Gap Movable Undulator Systems 1
  • F. Wolff-Fabris, Y. Li, J. Pflüger
    XFEL. EU, Schenefeld, Germany
  The European XFEL GmbH is a new X-ray FEL facility expected to be lasing to users at the end of 2017. Three gap-movable SASE Undulator Systems are designed to produce FELs with tunable wavelengths from 0.05 to 5.2nm.*,** A total of 91 5m long undulator segments and phase shifters were magnetically tuned respecting tight specifications. Magnetic field hysteresis effects due to the gap shift of the Undulator System while changing the FEL radiation wavelength may impact the machine's operational mode. We report on these effects by either opening or closing the gap while performing field integrals measurements with moving wire technique. The undulator segments show negligible magnetic hysteresis and are expected to be operated with no influence to the FEL and beam trajectories in either feed forward or feed backward mode. The phase shifters show first field integrals hysteretic behavior of few G.cm which is comparable in magnitude to the allowed total field integrals and can be associated to the magnetization of the yoke structure. Phase shifters are magnetically tuned for that the feed forward mode (opening gap) fully satisfies the XFEL. EU magnetic specifications for beam operation.
* M. Altarelli et al., Technical Design Rep. DESY 2006-097, July 2007.
** E. Schneidmiller et al., European XFEL Technical Rep. TR-2011-006, Sep. 2011.
WEP055 Tapered Flying Radiofrequency Undulator 1
  • S.V. Kuzikov, A.V. Savilov, A.A. Vikharev
    IAP/RAS, Nizhny Novgorod, Russia
  • S.P. Antipov, A. Liu
    Euclid TechLabs, LLC, Solon, Ohio, USA
  • A.V. Savilov
    UNN, Nizhny Novgorod, Russia
  Funding: This project is supported by DoE Small Business Innovative Research phase I grant #DE-SC0017145.
We propose an efficient XFEL consisting of sequential RF undulator sections using: 1) tapered flying RF undulators, 2) short pulse, high peak-power RF and 3) driving undulator sections by spent electron beam. In a flying RF undulator, an electron bunch propagates through a high-power, nanosecond, co-propagating RF pulse. Helical waveguide corrugation supports a space harmonic with a negative propagation constant, providing a large Doppler up-shift. The undulator tapering technique improves FEL efficiency by 1-2 orders of magnitude in comparison with other facilities by decreasing the undulator period so that particles are trapped in the combined field of the incident x-ray and undulator field. We develop a so-called non-resonant trapping regime not requiring phase locking for feeding RF sources. Simulations show that by decreasing the corrugation periodicity one can vary an equivalent undulator period by 15%. The spent electron beam can be used to produce wakefields that will drive the RF undulator sections for interaction with the following beam. We have already manufactured and tested the 30 GHz simplified version of the 50 cm long undulator section for cold measurements.
poster icon Poster WEP055 [1.561 MB]  
WEP056 Effect of Beam Transverse Angle Deflection in TGU on FEL Power 1
  • G. Zhou, J.Q. Wang
    IHEP, Beijing, People's Republic of China
  • J. Wu
    SLAC, Menlo Park, California, USA
  Funding: The work was supported by the US Department of Energy (DOE) under contract DE-AC02-76SF00515 and the US DOE Office of Science Early Career Research Program grant FWP-2013-SLAC-100164.
Recent study shows that electron beams with constant dispersion together with the transverse-gradient undulator (TGU) can reduce the sensitivity to energy spread for free-electron laser (FEL). By inducing dispersion function, electrons with different energy are placed at different positions corresponding to proper magnetic fields. Thus, FEL resonant condition can be kept for electrons with different energy. In this paper, we mainly studied: 1.The effects of electron beam angle deflection at the entrance of the TGU on the radiation power. 2. The utility of a kicker to introduce an angle deflection of electron beam to improve the FEL radiation power.
poster icon Poster WEP056 [0.633 MB]  
WEP057 Design of a Compact Hybrid Undulator for the THz Radiation Facility of Delhi Light Source (DLS) 1
  • S. Tripathi, R.K. Bhandari, S. Ghosh, D. Kanjilal
    IUAC, New Delhi, India
  • U. Lehnertpresenter
    HZDR, Dresden, Germany
  • M. Tischer
    DESY, Hamburg, Germany
  Funding: One author, Sumit Tripathi (PH/16-17/0029), would like to acknowledge University Grant Commission (UGC), New Delhi, India for financial support as D.S.Kothari Postdoctoral fellowship.
A compact Free Electron Laser (FEL) facility to produce coherent THz radiation is in the development stage at Inter-University Accelerator Centre (IUAC), New Delhi, India.*,** The name of this facility is Delhi Light Source (DLS) in which a low-emittance electron beam from a photocathode RF gun with a maximum energy of 8 MeV will be injected into a compact undulator magnet to generate THz radiation. To produce the THz radiation in the range of 0.15 to 3.0 THz, the electron beam energy and the undulator gap need to be varied from 4 to 8 MeV and 20 to 45 mm, respectively. The variable gap undulator of 1.5-m length will consist of NdFeB magnets with vanadium permendur poles. The magnet design and dimensions are optimised by using code 3D RADIA.*** The detailed design of the compact hybrid undulator will be presented in this paper.
* S.Ghosh et al., presented at this conference.
** S.Ghosh et al., NIMB-2017 (in press).
*** RADIA. Available at http://www.esrf.eu/Accelerators/ groups/
Insertion Devices/ Software/ Radia.
poster icon Poster WEP057 [1.112 MB]  
Development of a Hybrid Electromagnetic Planar Undulator Having Horizontal Focusing Force for a Compact THz FEL  
  • S. Bae, B.A. Gudkov, K.H. Jang, Y.U. Jeong, K. Lee, S.V. Miginsky, J. Mun, S. Park
    KAERI, Daejon, Republic of Korea
  • M.Y. Jeon
    Chungnam National University, Daejoen, Republic of Korea
  A THz table-top FEL is under development at KAERI for security applications. We developed a compact microtron to accelerate electrons up to 5 MeV with an energy spread of about 0.4%. A hybrid electromagnetic planar undulator was designed and fabricated to cover the FEL's lasing wavelength range of 400~600 μm. The magnetic field strength in the gap of the undulator is changeable from 0.76 to 1.14 T by varying the coil current of the undulator from 1.5 to 2.5 kA. The undulator provides a horizontal focusing force to keep the low energy electrons passing a specially-designed narrow waveguide. The undulator field error of 1st and 2nd integrals, which is 3.61 x 10-4 T·m and 5.75 x 10-5 T·m2, respectively, was minimized to reduce the deflection angle and trajectory offset of electron beam to pass through the waveguide having a width of 10 mm.  
Development of T-Ray-Pumped Ultrafast Electron Diffraction Beamline  
  • I.H. Baek, B. Han, K.H. Jang, Y.U. Jeong, H.W. Kim, M.H. Kim, Y.-C. Kim, K. Lee, J.H. Nam, S. Park
    KAERI, Daejon, Republic of Korea
  • N.A. Vinokurov
    NSU, Novosibirsk, Russia
  Ultrashort electron diffraction (UED) technique has triggered numerous fundamental studies and technological applications. For a resonant control of materials, the intense T-ray has been regarded as a crucial tool because its low photon energy can excite an extremely low energy level of atomic or molecular system selectively. In this work, we present the ultrafast T-ray-pump/electron-probe crystallography system for observing the structural dynamics of temperature-controlled materials. T-ray with energies of few microjoule is generated from the nonlinear optical crystal lithium niobate and utilized as a pumping source. Three-MeV electron bunches are produced by the RF-photogun with 2.856 GHz and utilized as a diffraction tool. The isochronous bending structure compresses an electron bunch length to ~30 femtoseconds. We believe that our system can guide the way to understand fundamental phenomena in nature.  
Characterizing Sub-Femtosecond X-ray Pulses from the Linac Coherent Light Source  
  • S. Li, R.N. Coffee, J. Cryan, K.H. Hegazy, Z. Huang, A. Marinelli, A. Natan, T. Osipov, D. Ray
    SLAC, Menlo Park, California, USA
  • G. Guo
    Stanford University, Stanford, California, USA
  The development of sub-femtosecond x-ray capabilities at the Linac Coherent Light Source requires the implementation of time-domain diagnostics with attosecond (as) time resolution. Photoelectrons created by attosecond duration x-ray pulses in the presence of a strong-laser field are known to suffer an energy spread which depends on the relative phase of the strong-laser field at the time of ionization. This phenomenon can be exploited to measure the duration of these ultrashort x-ray pulses. We present an implementation which employs a circularly polarized infrared laser pulse and novel velocity map imaging design which maps the phase dependent momentum of the photoelectron onto a 2-D detector. In this paper, we present the novel co-linear VMI design, simulation of the photoelectron momentum distribution, and the reconstruction algorithm.  
poster icon Poster WEP060 [1.256 MB]  
WEP061 Thermal Stress Analysis of a Thin Diamond Crystal Under Repeated Free Electron Laser Heat Load 1
  • J. Wu
    SLAC, Menlo Park, California, USA
  • B. Yang
    University of Texas at Arlington, Arlington, USA
  Funding: The work was supported by the US Department of Energy (DOE) under contract DE-AC02-76SF00515 and the US DOE Office of Science Early Career Research Program grant FWP-2013-SLAC-100164.
Thin crystals are used in many important optical elements, such as monochromator and spectrometer, in XFELs. To function properly, they must survive the ever-increasing heat load under repeated pulses. Here, we conduct a thermal stress analysis to examine the crystal lattice distortion due to the thermal load under various rep rates from 0.1 to 1 MHz. The thermal field is obtained by solving the transient heat transfer equations. The temperature-dependent material properties are used. It is shown that for pulse adsorption energy around tens of microjoule over a spot size of 10 micrometer, the thermal response of diamond is sensitive to rep rate. The thermal strain components are very different in the in- and out-of-plane directions, due to different constraint conditions. It suggests complicated strain effects in the Bragg and Laue diffraction cases.
WEP062 Optical Beam Quality Analysis of the Clara Test Facility Using Second Moment Analysis 1
  • H.M. Castaneda Cortes, D.J. Dunning, M.D. Roper, N. Thompson
    STFC/DL/ASTeC, Daresbury, Warrington, Cheshire, United Kingdom
  We studied and characterised the FEL optical radiation in simulations of the CLARA FEL test facility under development at Daresbury Laboratory in the UK. In particular, we determined the optical beam quality coefficient, waist position and other source properties corresponding to different potential FEL operating modes via wavefront propagation in free space using OPC (Optical Propagation Code) and Second Moment Analysis. We were able to find the operation mode and undulator design for which the optical beam has the optimum quality at highest brightness. Furthermore, we studied the way that different properties of the electron bunches (emittance, peak current, bunch length) affect the optical beam. We are now able to understand how the optical beam will propagate from the end of the undulator and through the photon transport system to the experimental stations. This knowledge is necessary for the correct design of the photon transport and diagnostic systems.  
poster icon Poster WEP062 [0.491 MB]  
WEP063 A Two-in-One Type Undulator 1
  • D. Wang, H.X. Deng, Z. Jiang
    SINAP, Shanghai, People's Republic of China
  Funding: This work is supported by the Ministry of Science and Technology of China.
The typical X-ray free electron lasers have long tunnels to accommodate high energy electron linear accelerator and long undulator line to produce intense coherent radiations at very short wavelengths. The number of undulator lines is limited by the available space in the tunnel. This is especially true for those facilities that adopt underground tunnels or utilize the existing tunnels originally built for other purpose. This work explored the possibility to better use the tunnel space for accommodating more FEL undulator lines by designing a new type of undulator structure.
WEP064 Tunable High-Gradient Quadrupoles for a Laser-Plasma Acceleration-Based FEL 1
  • A.M. Ghaith, F. Blache, M.-E. Couprie, C.A. Kitegi, F. Marteau, P. N'gotta, M. Valléau, J. Vétéran
    SOLEIL, Gif-sur-Yvette, France
  • C. Benabderrahmane
    ESRF, Grenoble, France
  • O. Cosson, F. Forest, P. Jivkov, J.L. Lancelot
    Sigmaphi, Vannes, France
  The magnetic design and characterization of tunable high gradient permanent magnet based quadrupole, are presented. To achieve a high gradient field with a compact structure, permanent magnets are chosen rather than usual electro-magnets due to their small aperture. The quadrupole structure consists of two quadrupoles superimposed capable of generating a gradient of 210 T/m. The first quadrupole is composed of permanent magnets following a Halbach configuration shaped as a ring attaining a constant gradient of 160T/m, and the second of four permanent magnet cylinders surrounding the ring and capable of rotating around their axis to achieve a gradient tunability of ±50 T/m. Each tuning magnet is connected to a motor and is controlled independently, enabling the gradient to be tuned with a rather good magnetic center stability (±20 μm) and without any field asymmetry. Seven quadrupoles have been built with different magnetic lengths in order to fulfil the integrated gradient required. A set of QUAPEVA triplet are now in use, to focus a high divergent electron beam with large energy spread generated by a laser plasma acceleration source for a free electron laser application.  
WEP065 Cryogenic Permanent Magnet Undulator for an FEL Application 1
  • A.M. Ghaith, T. André, I.A. Andriyash, P. Berteaud, F. Briquez, N. Béchu, M.-E. Couprie, C. Herbeaux, M. Labat, O. Marcouillé, F. Marteau, E. Roussel, M. Sebdaoui, K.T. Tavakoli, M. Tilmont, M. Valléau
    SOLEIL, Gif-sur-Yvette, France
  A Cryogenic Permanent Magnet Undulator (CMPU) is capable of achieving high brightness radiation at short wavelengths, by taking advantage of the permanent magnets' enhanced performance at low temperature. A CPMU of period 18 mm (U18) that has been built at Synchrotron SOLEIL is used for the COXINEL project to demonstrate Free Electron Laser (FEL) at 200 nm using a laser plasma acceleration source. Another undulator of period 15 mm (U15) is currently being built to replace U18 undulator for FEL demonstration at 40 nm. A new method is also introduced, using SRWE code, to compute the spectra of the large energy spread beam (few percent) taking into account the variation of the Twiss parameters for each energy slice. The construction of U18 undulator and the magnetic measurements needed for optimization, as well as the mechanical design of U15, are presented.  
Three-Dimensional, Time-Dependent Simulation of Free-Electron Lasers with Planar, Helical, and Elliptical Undulators  
  • H. Freund
    CSU, Fort Collins, Colorado, USA
  • P. Falgari
    Lime BV, Eindhoven, The Netherlands
  • D.L.A. Grimminck, I. Setya
    ASML, Veldhoven, The Netherlands
  • P.J.M. van der Slot
    Mesa+, Enschede, The Netherlands
  Free-electron lasers have been built ranging from long-wavelength oscillators through ultraviolet to hard x-ray that are either seeded or SASE. In addition, FELs that produce different polarizations ranging from linear through elliptic are currently under study. In this paper, we develop a 3D, time-dependent formulation that is capable of modeling this large variety of FEL configurations including different polarizations.* We employ a modal expansion for the optical field, i.e., a Gaussian expansion with variable polarization for free-space propagation. The formulation uses the Lorentz force equations to track particles. Arbitrary 3D representations for different undulators are implemented, including planar, helical, and elliptical. To model oscillators and allow propagation outside the undulator and interaction with optical elements, we link the FEL simulation with the optical propagation code OPC. We present detailed comparisons with experiments including (1) the LCLS, (2) the SPARC SASE FEL experiment at ENEA Frascati, (3) a seeded-tapered amplifier experiment at Brookhaven National Laboratory, and (4) the 10-kW Upgrade Oscillator experiment at Jefferson Laboratory.
* H.P. Freund, P.J.M. van der Slot, D.L.A.G. Grimminck, I.D. Setya, and P. Falgari, New J. Phys. 19, 023020 (2017).
Simulation of a Terawatt X-Ray Free-Electron Laser  
  • H. Freund
    CSU, Fort Collins, Colorado, USA
  The possibility of constructing terawatt x-ray free-electron lasers (FELs) has been discussed using novel superconducting helical undulators.* In this paper, we consider the conditions necessary for achieving powers in excess of 1 TW in a 1.5 Å FEL using the MINERVA simulation code.** Steady-state simulations have been conducted using a variety of undulator and focusing configurations. In particular, strong focusing using FODO lattices is compared with the natural, weak focusing inherent in helical undulators. It is found that the most important requirement to reach TW powers is extreme transverse compression of the electron beam in a strong FODO lattice.
* C. Emma, K. Fang, J. Wu, and C. Pellegrini, Phys. Rev. Accel. Beams, 19, 020705 (2016).
** H. Freund, P. van der Slot, D. Grimminck, I. Setya, and P. Falgari, New J. Phys. 19, 023020 (2017).
Distortion of the Spatial Properties of the Radiation from Seeded and SASE FEL Caused by Energy Chirp in the Electron Beam and Undulator Tapering  
  • E. Schneidmiller, M.V. Yurkovpresenter
    DESY, Hamburg, Germany
  Knowledge of the spatial properties of the radiation properties is a key issue for the users of x-ray FEL facilities. In this report, we present a detailed analysis of the spatial properties of the radiation from an FEL amplifier. Two configurations, seeded FEL amplifier, and SASE FEL, are under consideration. Dependence of the spatial distributions on the electron beam properties is studied, and their evolution along the undulator is traced. It is shown that spatial properties of the radiation may be significantly affected by the effect of energy chirp in the electron beam and undulator tapering.  
WEP073 Lie Map Formalism for FEL Simulation 1
  • K. Hwang, J. Qiang
    LBNL, Berkeley, California, USA
  Funding: U.S. Department of Energy under Contract No. DE-AC02-05CH11231
Undulator averaging and non-averaging are in compromisation between computational speed and reliability. It is hard to catch the advantages of the both methods simultaneously. In this report, we present a method that compromises the between the averaging and non-averaging methods through Lie map formalism.
WEP074 Simulations of the Dependence of Harmonic Radiation on Undulator Parameters 1
  • G. Penn
    LBNL, Berkeley, California, USA
  Funding: This work was supported by the Director, Office of Science, Office of Basic Energy Sciences, of the U.S. Department of Energy under Contract No. DE-AC02-05CH11231.
The flux and bandwidth of radiation produced at harmonics of the fundamental are very sensitive to the undulator parameter, and thus the beam energy or undulator period. We look at high-energy XFELs with parameters relevant to the MaRIE FEL design. Both SASE and seeded FELs are considered.
poster icon Poster WEP074 [0.410 MB]  
WEP078 Period-Averaged Symplectic Maps for the FEL Hamiltonian 1
  • S.D. Webb
    RadiaSoft LLC, Boulder, Colorado, USA
  Funding: This work was carried out with support for the United State Department of Energy, Office of Scientific Research, under SBIR contract number DE-SC0017161.
Conventional treatments of synchrotron radiation in electron beams treat the radiation as a non-Hamiltonian aspect to the beam dynamics. However, the radiation can be modeled with an electromagnetic Hamiltonian. We present a period-averaged treatment of the FEL problem which includes the Hamiltonian aspects of the coupled electron-radiation dynamics. This approach is then applied to two problems: a 3D split-operator symplectic integrator, and a 1D single-mode FEL treated using Hamiltonian perturbation theory.
High-Efficiency, Tapered FELs with a Pre-Bunched Electron Beam  
  • C. Emma, P. Musumeci, C. Pellegrini, N.S. Sudar, A. Urbanowicz
    UCLA, Los Angeles, USA
  • C. Pellegrini
    SLAC, Menlo Park, California, USA
  We study the 1-D physics of high gain, high efficiency tapered FELs in the post-saturation regime.*,** We derive a basic scaling formula for the FEL output power as a function of the beam current, the seed power and the trapping fraction assuming a constant resonant phase. We examine this analytic scaling using 1-D simulations for a seeded FEL starting from a large seed with a small energy spread electron beam (fresh bunch) with/without pre-bunching. We show that the efficiency improves substantially when the electron beam is suitably pre-bunched compared to the unbunched case. Finally, we study the sideband instability growth via 1-D time-dependent simulations. We confirm the inverse proportionality of the sideband power to the resonant phase as discussed in KMR. We also propose a method of sideband suppression via gain-modulation of the FEL using a modulated taper profile.***
* N. M. Kroll, P. L. Morton, and M. Rosenbluth. Quantum Electronics 17(8): 1436-1468, August 1981.
** R. Iaconescu, at this conference.
*** Marinelli et al., PRL 111: 134801 (2015).