Electron Guns, RF, Lasers, Cathodes
Paper Title Page
Photoemission from Diamond Field-Emitter Arrays  
  • V.N. Pavlenko, H.L. Andrews, R.L. Fleming, A. Piryatinski, D.Y. Shchegolkov, E.I. Simakov
    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.
We present experimental data on photoemission from diamond films, outlining future studies of diamond field emitter arrays (DFEAs) operation in photoemission mode. Nano-tipped field emitters are attractive types of electron sources for dielectric laser accelerators (DLAs),* whose ability to generate coherent electron bunches in laser-triggered mode has been successfully demonstrated.** To explore applicability of diamond field emitters to DLAs, we will measure spectral response (quantum efficiency vs photon energy) of DFEAs in the limit of low electric fields. We will compare the measurements on DFEAs with different densities and tip radii against bulk flat diamond photoemission. The results will be used to validate the a photoemission model that takes into account quantum confinement effects at the nano-tips of the pyramids.
* E. A. Peralta et al., Nature 503, 91 (2013)
** R. Ganter et al., Phys. Rev. Lett. 100, 064801 (2008); D. Ehberger et al., Phys. Rev. Lett. 114, 227601 (2015)
European XFEL Injector Commissioning Results  
  • B. Beutner
    DESY, Hamburg, Germany
  In the first commissioning phase of the European XFEL SASE FEL driver linac, we demonstrated the design goals for the injector section. These goals include reliable operation of sub-systems and feasible beam parameters like emittance and bunch length of the beam produced by the RF gun. Of particular interest is the operation of long bunch trains with up to 2700 bunches with a 4.5 MHz repetition rate. In this presentation we will provide an overview of our experiences from the injector commissioning run including beam dynamics studies, diagnostics, and system performance.  
slides icon Slides WEA01 [4.628 MB]  
WEA02 Model of Photocathode for CW Electron Gun 1
  • P.W. Huang, W.-H. Huang, C.-X. Tang
    TUB, Beijing, People's Republic of China
  Most of the proposed CW guns for free electron lasers use semiconductors as the photocathode due to their high quantum efficiency and potentially low thermal emittance. We manage to establish a model to explain the photoemission of semiconductors with incident photon energy above or below the theoretical threshold and derive the expression for quantum efficiency and thermal emittance. For the incident photon energy near or below the threshold of the cathode, things will be subtle and we should be careful to consider the details we used to neglect. The results of quantum efficiency and thermal emittance agree well with the published work. We also focus on the degradation of the semiconductors and propose a model to examine the development of the thermal emittance. We mainly consider the effect brought by the surface reactions with poisoning gases. The variation of quantum efficiency with time is well-consistent with experiment data. We also present the calculated results of thermal emittance, showing a decline with time. Similar results are presented with typical value of electric field in DC gun and RF gun.  
Simulation Optimization of DC-SRF Photoinjector for Low-Emittance Electron Beam Generation  
  • K.X. Liu, J.E. Chen, W. Cheng, L.W. Feng, J.K. Hao, S. Huang, L. Lin, W. Qin, S.W. Quan, F. Wang, H.M. Xie, F. Zhu
    PKU, Beijing, People's Republic of China
  A DC and superconducting rf (SRF) combined photoinjector, DC-SRF photoinjector, has been developed at Peking University to generate high repetition-rate electron bunches. At present stable operation of the DC-SRF photoinjector has been realized and the electron beam has been delivered to a SRF linac with two 9-cell TESLA-type cavities for further acceleration and experiments. Here we will present our latest progress on the DC-SRF photoinjector. We will also present our recent simulation work to decrease the emittance. The purpose is to build an upgraded DC-SRF photoinjector capable of driving CW X-ray free-electron lasers.  
WEA04 Novel Concepts of a High-Brightness Photoinjector RF Gun 1
  • S.V. Kuzikov, O.A. Ivanov, A.A. Vikharev, A.L. Vikharev
    IAP/RAS, Nizhny Novgorod, Russia
  • S.P. Antipov
    Euclid Beamlabs LLC, Bolingbrook, USA
  • S.P. Antipov
    Euclid TechLabs, LLC, Solon, Ohio, USA
  We propose here a program to design and manufacture a high performance, advanced source of electrons having high beam brightness (>1016 A/m2) and high bunch charge (~100 pC). Three innovations are being considered: 1) the use of a high peak cathode field, short-pulse RF gun; 2) the use of multi-layered diamond photocathode at low temperature; and 3) the utilization of THz ultrafast field emission gating. High peak cathode field is necessary to achieve a high brightness (low emittance) beam to be accelerated to relativistic energies before space-charge effects lengthen the bunch. The multilayered diamond photocathode is needed to obtain high QE with long wavelength laser in the first doped layer, beam cooling in the next layer, and negative electron affinity at the emission layer. High field single cycle THz pulses, produced by means of laser light rectification in a nonlinear crystal, allow to avoid a UV laser, provide high field emission charge (up to nC) and ~1 GV/m pre-acceleration of subpicosecond bunches.  
WEA05 Higher Fields and Beam Energies in Continuous-Wave Room-Temperature VHF RF Guns 1
  • F. Sannibale, J.M. Byrd, D. Filippetto, M.J. Johnson, D. Li, T.H. Luo, C.E. Mitchell, J.W. Staples, S.P. Virostek
    LBNL, Berkeley, California, USA
  Funding: Work supported by the Director of the Office of Science of the US Department of Energy under Contract no. DEAC02-05CH11231
The development in the last decade of MHz-class repetition rate free electron lasers (FELs), and ultrafast electron diffraction and microscopy (UED/UEM) applications, required new gun schemes capable of generating high-brightness beams at such high rates. The VHF-Gun, a 186 MHz room-temperature continuous-wave RF photogun developed at the Lawrence Berkeley Lab (LBNL) was an answer to that need. The VHF-Gun was constructed and tested in the APEX facility at LBNL successfully demonstrating all design parameters and the generation of FEL-quality electron beams. A close version of the APEX gun is in the final phase of fabrication at LBNL to operate as the electron source for the LCLS-II, the new SLAC X-ray FEL. The recently approved upgrade of the LCLS-II towards higher energies (LCLS-II HE) and the brightness-dependent UED and UEM applications would greatly benefit from an increased brightness of the electron source. Such performance upgrade can be obtained by increasing the electric field at the cathode and the beam energy at the gun exit. In this paper, we present and discuss possible upgrade options that would allow us to extend the VHF-Gun technology towards these new goals.
slides icon Slides WEA05 [4.320 MB]  
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. Krasilnikov, 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. Krasilnikov, 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. Stephan
    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. Stephan
    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. Krasilnikov, 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. Pavlenko
    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. Lorkiewicz, 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.