Author: Zhou, F.
Paper Title Page
MOP021 LCLS-II Injector Beamline Design and RF Coupler Correction 77
 
  • F. Zhou, D. Dowell, R.K. Li, T.O. Raubenheimer, J.F. Schmerge
    SLAC, Menlo Park, California, USA
  • C.E. Mitchell, C. F. Papadopoulos, F. Sannibale
    LBNL, Berkeley, California, USA
  • A. Vivoli
    Fermilab, Batavia, Illinois, USA
 
  Funding: U.S. DOE contract #DE-AC02-76SF00515.
LCLS-II CW injector beamline consists of a 186 MHz normal conducting (NC) RF gun for beam generation and acceleration to 750 keV, two solenoids for the beam focusing, two BPMs, 1.3 GHz NC RF buncher for bunch compression down to 3-4 ps rms, 1.3 GHz superconducting standard 8-cavity cryomodule to boost beam energy to about 98 MeV. The beamline is being optimized to accommodate all essential components and maximize beam quality. The beamline layouts and beam dynamics are presented and compared. The 3D RF field perturbation due to cavity couplers where the beam energy is very low (<1 MeV) causes significant emittance growth especially for a large-size beam. A theory of rotated fields predicted and simulations verified using a weak skew quadrupole located even a significant distance from the perturbation can completely eliminate the emittance growth. A layout for future upgrade is developed. The results are presented and analysed.
 
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MOD03 Alkali Cathode Testing for LCLS-II at APEX 280
 
  • H.J. Qian, J. Feng, D. Filippetto, J.R. Nasiatka, H.A. Padmore, F. Sannibale
    LBNL, Berkeley, California, USA
  • R.K. Li, J.F. Schmerge, F. Zhou
    SLAC, Menlo Park, California, USA
 
  Funding: Work supported by the Director of the Office of Science of the US Department of Energy under Contract no. DEAC02-05CH11231
Electron sources of high brightness and high bunch charge (~300 pC) with MHz repetition rate are one of the key technologies for next generation X-FEL facilities such as the LCLS-II at SLAC and the Euro XFEL at DESY. The Advanced Photoinjector EXperiment (APEX) at the Lawrence Berkeley National Laboratory (LBNL) is developing such an electron source based on high quantum efficiency (QE) alkali photocathodes and the VHF-Gun, a new scheme normal conducting RF gun developed at LBNL. The VHF-Gun already demonstrated stable CW operation with high gradient (~ 20 MV/m), high gun voltage (~ 750 kV) and low vacuum pressure (~ 3 E-10 torr) laying the foundation for the generation of high brightness electron beams. In this paper, we report the test and characterization of several different alkali cathodes in high average current (several hundreds of pC/bunch with MHz repetition rate) operation at APEX. Measurements include cathode life time, QE map evolution and thermal emittance characterization, to investigate the compatibility of such cathodes with the challenging requirements of LCLS-II.
 
slides icon Slides MOD03 [6.030 MB]  
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TUP072 Cathode Ion Bombardment in LCLS and LCLS-II RF Gun 534
 
  • L. Wang, A. Brachmann, F.-J. Decker, Z. Li, T.O. Raubenheimer, J.F. Schmerge, F. Zhou
    SLAC, Menlo Park, California, USA
 
  This paper studies the ions bombardment on the cathode in the LCLS and LCLS-II gun. APEX gun is used here for LCLS-II, which will be operate at 1 MHz repetition rate. Therefore, It is important to estimate the ion bombardment. One specific PIC code is used track arbitrary particles (ions and electron here) in arbitrary 2D/3D electromagnetic field and solenoid field to estimate the possibility of ion bombardment. The LCLS gun has 1.6 cells while the LCLS-II gun (APEX gun) is a half-cell gun. The frequencies of the two guns are also quite different. These characters make the ion dynamics quite differently. We estimated the bombardment for various ion species and studied the effects RF pulse shape and RF phase  
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WEP003 Recent Understanding and Improvements of the LCLS Injector 592
 
  • F. Zhou, D.K. Bohler, Y. Ding, S. Gilevich, Z. Huang, H. Loos, D.F. Ratner
    SLAC, Menlo Park, California, USA
 
  Funding: U.S. DOE contract No. DE-AC02-76SF00515.
Ultraviolet drive laser and copper photocathode are the key systems for reliably delivering <0.4 micron of emittance and high brightness free electron laser (FEL) at the linac coherent light source (LCLS). Characterizing, optimizing and controlling laser distributions in both spatial and temporal directions are important for ultra-low emittance generation. Spatial truncated Gaussian laser profile has been demonstrated to produce better emittance than a spatial uniform beam. Sensitivity of the spatial laser distribution for the emittance is measured and analysed. Stacking two 2-ps Gaussian laser beams significantly improves emittance and eventually FEL performance at the LCLS in comparison to a single 2-ps Gaussian laser pulse. In addition, recent observations at the LCLS show that the micro-bunching effect depends strongly on the cathode spot locations. The dependence of the micro-bunching and FEL performance on the cathode spot location is mapped and discussed.
 
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