Author: Qian, H.J.
Paper Title Page
TUOCA02 APEX Phase-II Commissioning Results at the Lawrence Berkeley National Laboratory 1041
  • F. Sannibale, J.A. Doyle, J. Feng, D. Filippetto, G.L. Harris, M.J. Johnson, T.D. Kramasz, D. Leitner, C.E. Mitchell, J.R. Nasiatka, H.A. Padmore, H.J. Qian, H. Rasool, J.W. Staples, S.P. Virostek, R.P. Wells, M.S. Zolotorev
    LBNL, Berkeley, California, USA
  • S.M. Gierman, R.K. Li, J.F. Schmerge, T. Vecchione, F. Zhou
    SLAC, Menlo Park, California, USA
  • C. Pagani, D. Sertore
    INFN/LASA, Segrate (MI), Italy
  Funding: Work supported by the Director of the Office of Science of the US Department of Energy under Contract no. DEAC02-05CH11231
Science needs in the last decade have been pushing the accelerator community to the development of high repetition rates (MHz/GHz-class) linac-based schemes capable of generating high brightness electron beams. Examples include X-ray FELs; ERLs for light source, electron cooling and IR to EUV FEL applications; inverse Compton scattering X-ray or gamma sources; and ultrafast electron diffraction and microscopy. The high repetition rate requirement has profound implications on the technology choice for most of the accelerator parts, and in particular for the electron gun. The successful performance of the GHz room-temperature RF photo-injectors running at rates <~ 100 Hz, cannot be scaled up to higher rates because of the excessive heat load that those regimes would impose on the gun cavity. In response to this gun need, we have developed at Berkeley the VHF-Gun, a lower-frequency room-temperature RF photo-gun capable of CW operation and optimized for the performance required by MHz-class X-ray FELs. The Advanced Photo-injector EXperiment (APEX) was funded and built for demonstrating the VHF gun performance, and the results of its last phase of commissioning are presented.
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DOI • reference for this paper ※ DOI:10.18429/JACoW-IPAC2016-TUOCA02  
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TUPOR019 RF Injector Beam Dynamics Optimization and Injected Beam Energy Constraints for LCLS-II 1699
  • C.E. Mitchell, H.J. Qian, J. Qiang, F. Sannibale, M. Venturini
    LBNL, Berkeley, California, USA
  • P. Emma, T.O. Raubenheimer, J.F. Schmerge, F. Zhou
    SLAC, Menlo Park, California, USA
  Funding: Work supported by the Office of Science of the US Department of Energy under Contract no. DEAC02-05CH11231.
LCLS-II is a proposed high-repetition rate (>1 MHz) Free Electron Laser (FEL) X-ray light source, based on a CW, superconducting linac, to be built at SLAC National Accelerator Laboratory. The injector technology is based on a high-repetition rate RF photoinjector gun developed as part of the Advanced Photoinjector Experiment (APEX) at Lawrence Berkeley National Laboratory. Exploration of the injector design settings is performed using a multiobjective genetic optimizer to optimize the beam quality at the injector exit (~100 MeV). In this paper, we describe the current status of LCLS-II injector design optimization, with a focus on the sensitivity of the optimized solutions to the beam energy at the injector exit, which is constrained by the requirements of the downstream laser heater system.
DOI • reference for this paper ※ DOI:10.18429/JACoW-IPAC2016-TUPOR019  
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WEPMY013 A Spatially Separated Two Frequency RF Gun Design for Beam Brightness Improvement 2572
  • Z. Zhang, C.-X. Tang, Z. Zhang
    TUB, Beijing, People's Republic of China
  • H.J. Qian
    LBNL, Berkeley, California, USA
  Recent theoretical and experimental studies shows that transverse beam brightness of photoinjector can be improved by cigar beam photoemission, and beam peak current are then increased with a RF buncher following the gun. We apply this concept to a S-band photoinjector by adding a harmonic RF buncher closely to a S-band RF gun, forming a compact spatially separated two frequency RF gun, targeting a 200 pC beam with emittance < 0.2 mm·mrad and 30 A peak current. Both S/X-band and S/C-band combinations are considered, and an optimized solution with 30 A peak current and 0.1 mm·mrad slice emittance are presented.  
DOI • reference for this paper ※ DOI:10.18429/JACoW-IPAC2016-WEPMY013  
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THPOW020 S-Band Photoinjector Investigations by Multiobjective Genetic Optimizer 3979
  • H.J. Qian, D. Filippetto, F. Sannibale
    LBNL, Berkeley, California, USA
  Photoinjectors has witnessed great progress in the past few decades, with low duty cycle high gradient guns, such as normal conducting S/L band gun, pushing the peak beam brightness frontier, and CW guns, such as DC gun, SRF gun and VHF gun, pushing the average beam brightness frontier. Due to different degrees of complexity, pulsed high gradient photoinjectors are usually optimized by manual scans, while CW photoinjectors are optimized by multi-objective genetic optimizers. In this paper, a multi-objective genetic optimizer is used to revisit S-band photoinjector beam brightness optimizations, showing a trade-off between peak current and transverse emittance, with the optimized injector layout depending on bunch charge and peak current. For 200 pC case, the final beam core brightness at injector exit is close to cathode maximum brightness in the 'cigar beam' regime. Assuming a thermal emittance of 0.5 μm/mm and a beam charge of 200 pC, about 90 nm slice emittance at 20 A peak current is achieved.  
DOI • reference for this paper ※ DOI:10.18429/JACoW-IPAC2016-THPOW020  
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