Author: Huang, R.
Paper Title Page
TUA01
 APEX: A Photo-injector for High Average Power Light Sources and Beyond  
 
  • D. Filippetto, C.W. Cork, S. De Santis, L.R. Doolittle, G. Huang, R. Huang, W.E. Norum, C. F. Papadopoulos, G.J. Portmann, H.J. Qian, F. Sannibale, J.W. Staples, R.P. Wells
    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
Direct observation of structural dynamics in complex systems calls for a new generation of ultrafast instruments with enhanced average brightness and increased stability. The APEX electron source at LBNL was conceived and built for answering that demand. It combines ultra-short bunches and high accelerating fields of rf guns, with high-repetition-rate, stability and reliability typical of CW sources. The successful demonstration of the source key performances, such as accelerating field, emittance and beam current, would enable high repetition rate operations for applications such as X-Ray FELs, and ultrafast electron diffraction. We present the latest results, including cathode tests, photo-beam and dark current characterization, laser and beam jitter results, and future plans. 		 
slides icon Slides TUA01 [18.646 MB]  
 
THP019 Higher-Order Moment Models of Longitudinal Pulse Shape Evolution in Photoinjectors 722
 
  • C.E. Mitchell, D. Filippetto, R. Huang, C. F. Papadopoulos, H.J. Qian, J. Qiang, F. Sannibale, M. Venturini
    LBNL, Berkeley, California, USA
  
  The presence of longitudinal asymmetry, sometimes in the form of a one-sided tail, in the current profile emerging from low-energy photoinjectors can strongly impact the beam quality downstream of the compression system of the FEL beam delivery system. To understand the origin of this feature, an approximate model for the evolution of higher-order beam moments is developed in the presence of nonlinear kinematic effects and longitudinal space-charge. This model is applied to investigate the evolution of beam skewness for injector systems with parameters similar to the APEX Injector under investigation at Lawrence Berkeley National Laboratory.  
 
THP042 The LCLS-II Injector Design 815
 
  • J.F. Schmerge, A. Brachmann, D. Dowell, A.R. Fry, R.K. Li, Z. Li, T.O. Raubenheimer, T. Vecchione, F. Zhou
    SLAC, Menlo Park, California, USA
  • A.C. Bartnik, I.V. Bazarov, B.M. Dunham, C.M. Gulliford, C.E. Mayes
    Cornell University (CLASSE), Cornell Laboratory for Accelerator-Based Sciences and Education, Ithaca, New York, USA
  • D. Filippetto, R. Huang, C. F. Papadopoulos, G.J. Portmann, J. Qiang, F. Sannibale, S.P. Virostek, R.P. Wells
    LBNL, Berkeley, California, USA
  • A. Lunin, N. Solyak, A. Vivoli
    Fermilab, Batavia, Illinois, USA
  
  The new LCLS-II project will construct a 4 GeV continuous wave (CW) superconducting linear accelerator to simultaneously feed two undulators which will cover the spectral ranges 0.2-1.2 keV and 1-5 keV, respectively. The injector must provide up to 300 pC/bunch with a normalized emittance < 0.6 mm and peak current > 30 A at up to 1 MHz repetition rate. An electron gun with the required brightness at such high repetition rate has not yet been demonstrated. However, several different options have been explored with results that meet or exceed the performance requirements of LCLS-II. The available technologies for high repetition-rate guns, and the need to keep dark current within acceptable values, limit the accelerating gradient in the electron gun. We propose a CW normal conducting low frequency RF gun for the electron source due to a combination of the simplicity of operation and the highest achieved gradient in a CW gun, potentially allowing for lower beam emittances. The high gradient is especially significant at the 300 pC/bunch charge where beam quality can suffer due to space charge. This paper describes the design challenges and presents our solutions for the LCLS-II injector.  
 
THP057 Longitudinal and Transverse Optimization for a High Repetition Rate Injector 864
 
  • C. F. Papadopoulos, D. Filippetto, R. Huang, G.J. Portmann, H.J. Qian, F. Sannibale, S.P. Virostek, R.P. Wells
    LBNL, Berkeley, California, USA
  • A.C. Bartnik, I.V. Bazarov, B.M. Dunham, C.M. Gulliford, C.E. Mayes
    Cornell University (CLASSE), Cornell Laboratory for Accelerator-Based Sciences and Education, Ithaca, New York, USA
  • A. Brachmann, D. Dowell, P. Emma, Z. Li, T.O. Raubenheimer, J.F. Schmerge, T. Vecchione, F. Zhou
    SLAC, Menlo Park, California, USA
  • A. Vivoli
    Fermilab, Batavia, Illinois, USA
  
  Funding: Work supported by the Director of the Office of Science of the US Department of Energy under Contract no. DEAC02-05CH11231
The injector is the low energy part of a linac, where space charge and kinematic effects may affect the electron beam quality significantly, and in the case of single pass systems determines the brightness in the downstream components. Following the increasing demand for high repetition rate user facilities, the VHF-gun, a normal conducting, high repetition rate (1 MHz) RF gun operating at 186 MHz has been constructed at LBNL within the APEX project and is under operation. In the current paper, we report on the status of the beam dynamics studies. For this, a multi-objected approach is used, where both the transverse and the longitudinal phase space quality is optimized, as quantified by the transverse emittance and the bunch length and energy spread respectively. We also report on different bunch charge operating modes. 		 
 
THP054 Dark Current Studies at the APEX Photoinjector 855
 
  • R. Huang
    USTC/NSRL, Hefei, Anhui, People's Republic of China
  • D. Filippetto, C. F. Papadopoulos, F. Sannibale
    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 increasing scientific demand for a high repetition rate FEL light source is driving the development of electron sources with high beam quality, delivering electron bunches at rates in the MHz range. An ongoing project to develop such a source is the Advanced Photoinjector Experiment (APEX) at LBNL. High brightness electron beams require high fields at the cathode during the electron emission. Such high fields associated with imperfections on the cathode surface area can induce undesired electron field emission (dark current). Excessive dark current can generate quenching of SRF structures and undesired radiation doses activating accelerator components and damaging undulator structures. In the present paper, we discuss the dark current studies performed at APEX. Field emitters in the cathode area have been localized and characterized, and techniques for minimizing dark current emission and to passively remove it have been investigated.