Keyword: cathode
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WEA01 Overview of CW RF Guns for Short Wavelength FELs gun, FEL, SRF, electron 290
 
  • H.J. Qian
    DESY Zeuthen, Zeuthen, Germany
  • E. Vogel
    DESY, Hamburg, Germany
 
  Hard X-ray FELs (XFELs) operating with pulsed RF provide unprecedented peak brilliance for scientific research. Operating the accelerators with CW RF improves the flexibility w.r.t. the available time structure for experiments and opens the next frontier of average brilliance. One of the challenges of CW XFELs is the electron source, which requires both CW operation and highest possible beam quality allowing lasing at shortest wavelengths. The CW mode technically constraints the gun acceleration gradient, which is one of the keys to electron source brightness, so R&D is devoted to CW gun improvements since decades. In this contribution, the worldwide development status of CW RF guns, both normal conducting and superconducting, is reviewed.  
slides icon Slides WEA01 [16.329 MB]  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-FEL2019-WEA01  
About • paper received ※ 25 August 2019       paper accepted ※ 07 November 2019       issue date ※ 05 November 2019  
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WEA04 Growing and Characterization of Cs2Te Photocatodes with Different Thicknesses at INFN LASA electron, gun, diagnostics, FEL 297
 
  • L. Monaco, P. Michelato, D. Sertore
    INFN/LASA, Segrate (MI), Italy
  • G. Guerini Rocco, C. Pagani
    Università degli Studi di Milano & INFN, Segrate, Italy
 
  The INFN LASA group has a long standing experience in the production of cesium telluride photocathodes for high brightness photoinjectors. The well-established recipe relies on the deposition of a typical amount of 10 nm of Te, followed by the Cs deposition until reaching the maximum QE. Nevertheless, for improving the understanding of photocathode properties, we are investigating the effect of Te thickness on the growing process, evaluating photocathode optical properties and quantum efficiency during the growing process and on the final film. These photocathodes will be then operated and analyzed in the real environment of the RF Gun at the PITZ facility in DESY Zeuthen, to estimate their impact on the electron beam properties.  
slides icon Slides WEA04 [15.703 MB]  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-FEL2019-WEA04  
About • paper received ※ 20 August 2019       paper accepted ※ 27 August 2019       issue date ※ 05 November 2019  
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WEP045 Status of the Klystrons for the European XFEL after Commissioning and First User Operation Phase FEL, klystron, operation, linac 420
 
  • V. Vogel (Fogel), M. Bousonville, A. Cherepenko, S. Choroba, H.-J. Eckoldt, T. Grevsmühl, V.V. Katalev, K. Machau, P. Morozov, B. Yildirim
    DESY, Hamburg, Germany
 
  At present 26 RF stations for the European XFEL are in operation. Each of the RF stations consists of a HV modulator located on the DESY campus, up to 1600 m long 10 kV HV cables that connect the modulators and the HV pulse transformers located in the underground tunnel, the horizontal multi-beam klystron (MBK), and an air filled waveguide distribution system (WG) between the klystron and the cavities input couplers. The klystrons can produce RF power up to 10 MW, 1.5 ms RF pulse length and 10 Hz repetition rate. Two RF stations of the injector have already achieved about 30,000 hours of operation, RF stations of the XFEL bunch compressor area have operated up to 20,000 hours and the klystrons in the XFEL main linac already have about 18,000 hours of operation. To increase the lifetime of the klystrons we are using a fast protection system (KLM) that is in routine operation since 2018 in addition to the common interlock system. In this article we will give a summary of the present klystrons operation status including the number of HV and RF arcs in the klystrons and in the WG system and operation statistics for the high power RF part of machine.  
poster icon Poster WEP045 [0.757 MB]  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-FEL2019-WEP045  
About • paper received ※ 20 August 2019       paper accepted ※ 12 September 2019       issue date ※ 05 November 2019  
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WEP046 The European XFEL Photocathode Laser laser, FEL, electron, controls 423
 
  • L. Winkelmann, A. Choudhuri, U. Grosse-Wortmann, I. Hartl, C. Li, C. Mohr, J. Müller, F. Peters, S. Pfeiffer, S.H. Salman
    DESY, Hamburg, Germany
 
  We present the Yb:fiber, Nd:YVO4 laser used to generate electrons from the RF photocathode gun at the European XFEL. The laser provides deep UV output pulses in 600 µs bursts with variable internal repetition rate (564 kHz to 4.5 MHz). Due to its robust architecture (mode-locked and synchronized fiber oscillator, Yb:fiber amplifiers and Nd:YVO4 gain blocks), the laser has operated with >99% uptime since January 2017. Using this laser, the XFEL reported energies of 17.5 GeV in July 2018, and simultaneous multi-mJ lasing in its three SASE beamlines. The laser offers two parallel outputs (1064 nm) with single pulse energies of >100 µJ and 11 ps width (FWHM). One output is converted to deep UV with efficiencies > 25%, and the second is used as a laser heater to reduce microbunching instabilities to increase SASE efficiency. Several state-of-art laser controls were implemented, including feed-forward algorithm to flatten electron charge along the bunch, active beam stabilization with < ±10 µm jitter at the photocathode, state machines for hands-off end-user operation, and temporal pulse synchronization and drift compensation to the timing jigger of the electron bunches to less than 45 fs.  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-FEL2019-WEP046  
About • paper received ※ 23 August 2019       paper accepted ※ 29 August 2019       issue date ※ 05 November 2019  
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WEP047 Update on the Photocathode Lifetime at FLASH and European XFEL FEL, laser, gun, operation 427
 
  • S. Lederer, F. Brinker, S. Schreiber
    DESY, Hamburg, Germany
  • L. Monaco, D. Sertore
    INFN/LASA, Segrate (MI), Italy
 
  The photoinjectors of FLASH and the European XFEL at DESY (Hamburg, Germany) are operated by laser driven RF-guns. In both facilities Cs2Te photocathodes are successfully used. In this paper we give an update on the lifetime, quantum efficiency (QE) and dark current of the photocathodes used over the last years. At FLASH cathode #73.3 was operated for a record lifetime of 1413 days and was replaced December 2018 by cathode #105.2. At the European XFEL cathode #680.1 is in operation since December 2015, for 1356 days up to now.  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-FEL2019-WEP047  
About • paper received ※ 20 August 2019       paper accepted ※ 28 August 2019       issue date ※ 05 November 2019  
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WEP048 FLASH Photoinjector Laser Systems laser, electron, operation, free-electron-laser 430
 
  • S. Schreiber, C. Grün, K. Klose, J. Rönsch-Schulenburg, B. Steffen
    DESY, Hamburg, Germany
 
  The free-electron laser facility FLASH at DESY (Hamburg, Germany) operates two undulator beamlines simultaneously for FEL operation and a third for plasma acceleration experiments (FLASHForward). The L-band superconducting technology allows accelerating fields of up to 0.8 ms in length at a repetition rate of 10 Hz (burst mode). A fast kicker-septum system picks one part of the 1 MHz electron bunch train and kicks it to the second beamline such that two beamlines are operated simultaneously with the full repetition rate of 10 Hz. The photoinjector operates three laser systems. They have different pulse durations and transverse shapes and are chosen to serve best for the given user experiment in terms of electron bunch charge, bunch compression, and bunch pattern. It is also possible to operate the laser systems on the same beamline to provide specific double pulses for certain type of experiments.  
poster icon Poster WEP048 [2.642 MB]  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-FEL2019-WEP048  
About • paper received ※ 26 August 2019       paper accepted ※ 27 August 2019       issue date ※ 05 November 2019  
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WEP051 PITZ Experimental Optimization for the Aimed Cathode Gradient of a Superconducting CW RF Gun emittance, gun, laser, SRF 440
 
  • M. Krasilnikov, P. Boonpornprasert, Y. Chen, G.Z. Georgiev, J.D. Good, M. Groß, P.W. Huang, I.I. Isaev, C. Koschitzki, S. Lal, X. Li, O. Lishilin, G. Loisch, D. Melkumyan, R. Niemczyk, A. Oppelt, H.J. Qian, H. Shaker, G. Shu, F. Stephan, G. Vashchenko
    DESY Zeuthen, Zeuthen, Germany
  • M. Dohlus, E. Vogel
    DESY, Hamburg, Germany
 
  A continuous wave (CW) mode operation of the European X-ray Free-Electron Laser (XFEL) is under considerations for a future upgrade. Therefore, a superconducting radio frequency (SRF) CW gun is under experimental development at DESY in Hamburg. Beam dynamics simulations for this setup have been done assuming 100 pC bunch charge and a maximum electric field at the photocathode of 40 MV/m. Experimental studies for these parameters using a normal conducting RF photogun have been performed at the Photo Injector Test facility at DESY in Zeuthen (PITZ). The beam transverse emittance was minimized by optimizing the main photo injector parameters in order to demonstrate the feasibility of generating electron beams with a beam quality required for successful CW operation of the European XFEL for conditions similar to the SRF gun setup.  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-FEL2019-WEP051  
About • paper received ※ 20 August 2019       paper accepted ※ 27 August 2019       issue date ※ 05 November 2019  
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WEP052 Simulation Studies on the Saturated Emission at PITZ laser, space-charge, gun, simulation 444
 
  • X. Li, P. Boonpornprasert, Y. Chen, J.D. Good, M. Groß, I.I. Isaev, C. Koschitzki, M. Krasilnikov, S. Lal, O. Lishilin, G. Loisch, D. Melkumyan, R. Niemczyk, A. Oppelt, H.J. Qian, H. Shaker, G. Shu, F. Stephan, G. Vashchenko
    DESY Zeuthen, Zeuthen, Germany
 
  In this paper we report our consideration and simulation on the space charge dominated emission in the L-band photocathode RF gun at the Photo Injector Test facility at DESY in Zeuthen (PITZ). It has been found that the emission curve, which relates the extracted and accelerated bunch charge after the gun to the laser energy, doesn’t agree very well with Astra simulations when the emission is nearly or fully saturated. Previous studies with a core-halo model for a better fit of the experimentally measured laser transverse profile as well as with an improved transient emission model have resulted in a better agreement between experimental data and simulation. A 3D FFT space charge solver including mirror charge and binned energy/momentum has been built, which also allows more emission mechanisms to be included in the future. In this paper, the energy spread during emission was preliminarily analyzed. Experimentally measured emission curves were compared with simulation, showing the effect of the inhomogeneity of the laser on the emission and beam parameters.  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-FEL2019-WEP052  
About • paper received ※ 20 August 2019       paper accepted ※ 27 August 2019       issue date ※ 05 November 2019  
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WEP053 Development of a Multialkali Antimonide Photocathode at INFN LASA laser, gun, site, electron 448
 
  • S.K. Mohanty
    DESY Zeuthen, Zeuthen, Germany
  • G. Guerini Rocco, C. Pagani
    Università degli Studi di Milano & INFN, Segrate, Italy
  • P. Michelato, L. Monaco, D. Sertore
    INFN/LASA, Segrate (MI), Italy
 
  Owing to their excellent properties including high quantum efficiency (QE), low emittance, good lifetime and fast response, alkali antimonides photocathodes has been considered as one of the eminent candidates for the electron source of energy recovery linacs (ERL) and free electron lasers (FEL). Nevertheless, their sensitivity to vacuum condition requires specific R&D before they can operate in a RF Gun. For this reason, we have started to develop specifically K-Cs-Sb based multialkali photocathodes at INFN LASA. The primary goal is to develop a stable and reproducible alkali antimonide films on INFN plugs and test them in the photoinjector test facility PITZ at DESY Zeuthen. In this report, we present and discuss about the results so far obtained on KCsSb material and the status of the new preparation system specifically designed for these sensitive materials.  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-FEL2019-WEP053  
About • paper received ※ 08 August 2019       paper accepted ※ 27 August 2019       issue date ※ 05 November 2019  
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WEP054 Beam Dynamics Optimization of a Normal-Conducting Gun Based CW Injector for the European XFEL cavity, gun, FEL, cryomodule 452
 
  • H. Shaker, S. Lal, H.J. Qian, G. Shu, F. Stephan
    DESY Zeuthen, Zeuthen, Germany
 
  The European XFEL is operating up to 17.5 GeV electron energy with maximum 0.65% duty cycle. There is a prospect for continuous wave and long pulse mode (CW/LP) operation of the European XFEL, which enables more flexible bunch pattern time structure for experiments, higher average brightness and better stability. Due to engineering limitations, the maximum electron beam energy in the CW/LP mode is about 8.6/12.8 GeV, which puts more pressure on the injector beam quality for lasing at the shortest wavelength. This paper optimizes the beam dynamics of an injector based on a normal-conducting VHF gun.  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-FEL2019-WEP054  
About • paper received ※ 20 August 2019       paper accepted ※ 26 August 2019       issue date ※ 05 November 2019  
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WEP056 Engineering Design of Low-Emittance DC-SRF Photocathode Injector SRF, cavity, linac, shielding 460
 
  • Y.Q. Liu, M. Chen, S. Huang, L. Lin, K.X. Liu, S.W. Quan, F. Wang, S. Zhao
    PKU, Beijing, People’s Republic of China
 
  An upgraded version of DC-SRF photocathode injector (DC-SRF-II) is under development at Peking University. The goal is to achieve an emittance below 0.5 mm-mrad at the bunch charge of 100 pC and repetition rate of 1 MHz. The engineering design of the DC-SRF-II photoinjector was accomplished in this May and the fabrication is ongoing now. This paper presents some details of the engineering design.  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-FEL2019-WEP056  
About • paper received ※ 19 August 2019       paper accepted ※ 26 August 2019       issue date ※ 05 November 2019  
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WEP058 Drive Laser Temporal Shaping Techniques for Shanghai Soft X-Ray Free Electron Laser laser, electron, FEL, flattop 466
 
  • X.T. Wang, T. Lan, M. Zhang, W.Y. Zhang
    SINAP, Shanghai, People’s Republic of China
  • L. Feng, B. Liu
    SARI-CAS, Pudong, Shanghai, People’s Republic of China
  • C.L. Li
    Shanghai Advanced Research Institute, Pudong, Shanghai, People’s Republic of China
 
  The design of Shanghai soft X-ray free electron laser (SXFEL) is based on laser driven photocathode, which can provide emittance <2.0 mm’mrad with 500 pC charge. The temporal shape of drive laser has significant influence on the electron beam emittance and brightness. This paper presents the transport line of drive laser system and the temporal shaping techniques for SXFEL. This drive laser produces 8 picosecond 266nm ultraviolet pulses with repetition rate 10Hz. A transverse deflecting cavity was used for indirectly characterizing the laser pulse temporal structure. Here we present the drive laser system with its temporal shaping method, and measurement results.  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-FEL2019-WEP058  
About • paper received ※ 20 August 2019       paper accepted ※ 28 August 2019       issue date ※ 05 November 2019  
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WEP062 Test of Cs2Te Thickness on Cathode Performance at PITZ emittance, gun, laser, FEL 473
 
  • P.W. Huang
    TUB, Beijing, People’s Republic of China
  • Y. Chen, M. Groß, I.I. Isaev, P. Kitisri, C. Koschitzki, M. Krasilnikov, S. Lal, X. Li, O. Lishilin, D. Melkumyan, R. Niemczyk, A. Oppelt, H.J. Qian, H. Shaker, G. Shu, F. Stephan, G. Vashchenko, T. Weilbach
    DESY Zeuthen, Zeuthen, Germany
  • A. Grigoryan
    CANDLE, Yerevan, Armenia
  • S. Lederer
    DESY, Hamburg, Germany
  • P. Michelato, L. Monaco, D. Sertore
    INFN/LASA, Segrate (MI), Italy
 
  Cesium telluride is a widely used cathode in photo injectors, and its performance is one of the keys for not only emittance but also reliable operation. Over the years lots of experiences with Cs2Te photocathodes produced with the same recipe and thickness were gained at the DESY photo injectors, but cathode performance dependence on the cathode layer thickness were not investigated. In this paper, we test fresh Cs2Te cathodes with different thickness at the Photo Injector Test Facility at DESY in Zeuthen (PITZ). The QE and thermal emittance of these cathodes inside the high gradient RF gun will be compared. Besides, the injector emittance under the operation conditions of the XFEL will also be measured with these cathodes.  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-FEL2019-WEP062  
About • paper received ※ 20 August 2019       paper accepted ※ 27 August 2019       issue date ※ 05 November 2019  
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WEP064 Performance of S-Band Photocathode RF Gun With Coaxial Coupler gun, electron, laser, FEL 481
 
  • J.H. Hong, J.H. Han, C.-K. Min
    PAL, Pohang, Kyungbuk, Republic of Korea
 
  To improve the characteristics of electron beams, new S-band photocathode RF gun with a coaxial coupler has been developed and fabricated at the Pohang Accelerator Laboratory (PAL). This new RF gun is improved the field symmetry inside the cavity cell by applying the coaxial coupler, and the cooling performance by improving the cooling lines. The RF gun is installed in the injector test facility (ITF) for high power RF test. This paper reports the recent results on the RF conditioning process and the beam tests of the RF gun with high power RF at ITF. We present and discuss the measurement results of the basic beam parameters.  
poster icon Poster WEP064 [0.784 MB]  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-FEL2019-WEP064  
About • paper received ※ 24 August 2019       paper accepted ※ 26 August 2019       issue date ※ 05 November 2019  
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