Keyword: cathode
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MOP046 Progress of Delhi Light Source at IUAC, New Delhi ion, electron, laser, undulator 149
 
  • S. Ghosh, S. R. Abhilash, R.K. Bhandari, G.K. Chaudhari, V.J. Joshi, D. Kabiraj, D. Kanjilal, B. Karmakar, J. Karmakar, N. Kumar, S. Kumar, A. Pandey, P. Patra, G.O. Rodrigues, B.K. Sahu, A. Sharma, S. Tripathi
    IUAC, New Delhi, India
  • A. Aryshev, M.K. Fukuda, S. Fukuda, N. Terunuma, J. Urakawa
    KEK, Ibaraki, Japan
  • U. Lehnert, P. Michel
    HZDR, Dresden, Germany
  • V. Naik, A. Roy
    VECC, Kolkata, India
  • T. Rao
    BNL, Upton, Long Island, New York, USA
  • M. Tischer
    DESY, Hamburg, Germany
 
  Funding: This project is jointly supported by Inter University Accelerator Center and Board of Research in Nuclear Science.
The first phase of the pre-bunched FEL based on the Photoinjector RF electron gun, known as Delhi Light Source (DLS),* has been planned at Inter University Accelerator Centre (IUAC), New Delhi. The electron gun made from OFHC copper had already been fabricated and tested with low power RF at KEK, Japan. The beam optics calculation by using ASTRA, GPT codes has been performed and radiation produced from the pre-bunched electron bunches are being calculated.** The high power RF systems will be commissioned at IUAC by the beginning of 2018. The design of the laser system is being finalized and assembly/testing of the complete laser system will be started soon at KEK. The initial design of the photocathode deposition mechanism has also been completed and its procurement/development process will start shortly. The first version of the undulator magnet design has been completed and further improvements are underway.*** The initial arrangements of the DLS beam line have been worked out and various beam diagnostics components are being finalised. The production of the electron beam and THz radiation is expected by 2018 and 2019, respectively.
* S. Ghosh et al., NIM-B, (2017) in press.
** V. Joshi et al., Proc. of this conference.
*** S. Tripathi et al., Proc. of this conference.
 
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DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-FEL2017-MOP046  
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MOP050 Present Status of Infrared FEL Facility at Kyoto University ion, FEL, undulator, operation 162
 
  • H. Zen, T. Kii, S. Krainara, K. Masuda, H. Ohgaki, J. Okumura, S. Suphakul, S. Tagiri, K. Torgasin
    Kyoto University, Kyoto, Japan
 
  A mid-infrared free electron laser (FEL) named KU-FEL has been developed for promoting energy-related research at the Institute of Advanced Energy, Kyoto University.* KU-FEL can cover the wavelength range from 3.6 to 23 micrometers and is routinely operated for internal and external user experiments. Recently a THz Coherent Undulator Radiation (CUR) source using a photocathode RF gun has been developed as an extension of the facility.* As the result of commissioning the experiment, it was confirmed that the CUR source can cover the frequency range from 160 to 550 GHz. Present status of these infrared light sources will be presented.
* H. Zen et al., Physics Procedia 84, pp.47-53 (2016).
 
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-FEL2017-MOP050  
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WEA02 Model of Photocathode for CW Electron Gun ion, electron, emittance, scattering 394
 
  • 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.  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-FEL2017-WEA02  
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WEA04 Novel Concepts of a High-Brightness Photoinjector RF Gun ion, electron, gun, brightness 397
 
  • 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.  
slides icon Slides WEA04 [4.039 MB]  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-FEL2017-WEA04  
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WEA05 Higher Fields and Beam Energies in Continuous-Wave Room-Temperature VHF RF Guns ion, gun, electron, brightness 401
 
  • 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]  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-FEL2017-WEA05  
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WEP003 Update on the Lifetime of Cs2Te Photocathodes Operated at FLASH ion, laser, gun, operation 415
 
  • 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 [0.286 MB]  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-FEL2017-WEP003  
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WEP006 Preliminary On-Table and Photoelectron Results from the PITZ Quasi-Ellipsoidal Photocathode Laser System ion, laser, electron, emittance 426
 
  • 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.M. 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 [1.766 MB]  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-FEL2017-WEP006  
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WEP008 Beam Brightness Improvement by Ellipsoidal Laser Shaping for CW Photoinjectors ion, emittance, gun, laser 432
 
  • 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.  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-FEL2017-WEP008  
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WEP009 A Cryocooled Normal-Conducting and Superconducting Hybrid CW Photoinjector cavity, ion, gun, SRF 436
 
  • 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.  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-FEL2017-WEP009  
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WEP012 A 2.45 GHz Photoinjector Gun for an FEL Driven by Laser Wakefield Accelerated Beam ion, laser, klystron, cavity 444
 
  • 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.
 
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DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-FEL2017-WEP012  
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WEP014 Pulse Duration Measurement of Pico-second DUV Photocathode Driving Laser by Autocorrelation Technique Using Two-Photon Absorption in Bulk Material ion, laser, electron, gun 447
 
  • 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).
 
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WEP015 Current Experimental Work with Diamond Field-Emitter Array Cathodes ion, experiment, electron, site 450
 
  • 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.
 
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-FEL2017-WEP015  
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WEP016 Modeling of Diamond Field-Emitter Arrays for High-Brightness Photocathode Applications ion, electron, simulation, scattering 454
 
  • 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.
 
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WEP021 Preliminary Results of the Dark Current Modelling for the Polfel Superconducting Lead Photocathode ion, cavity, gun, electron 463
 
  • 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.  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-FEL2017-WEP021  
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WEP025 Emittance Measurements from SRF Gun in CeC Accelerator ion, gun, emittance, solenoid 470
 
  • 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.
 
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-FEL2017-WEP025  
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