Author: Vetter, S.
Paper Title Page
THP030 Recent Photocathode R&D for the LCLS injector 769
 
  • F. Zhou, A. Brachmann, W.J. Corbett, M.J. Ferreira, S. Gilevich, E.N. Jongewaard, J.R. Lewandowski, J. Sheppard, T. Vecchione, S. Vetter, S.P. Weathersby
    SLAC, Menlo Park, California, USA
 
  Funding: US DOE under contract No. DE-AC02-76SF00515
Sys­tem­atic stud­ies of the cop­per pho­to­cath­odes iden­ti­cal to those used in the LCLS in­jec­tor gun has been car­ried out at SLAC’s RF gun test fa­cil­ity. Re­cent ob­ser­va­tions at the gun test fa­cil­ity in­di­cate that the pre-clean­ing of the cath­ode prior to the in­stal­la­tion in the gun is the major cause of the lower ini­tial QE (~10-6) in the RF gun. All of four cath­odes tested in the gun test fa­cil­ity have re­li­able higher ini­tial QE, 4-8·10-5, with re­moval of pre-clean­ing step. All of de­tails will be de­scribed in the paper. A ro­bust laser-as­sisted pro­cess­ing recipe has been de­vel­oped. With this recipe, QE can be re­peat­edly evolved to about 1x10-4 within 3-4 weeks fol­low­ing the laser pro­cess­ing, and within 1-2 days the emit­tance is re­cov­ered to the val­ues as ob­served prior to the laser pro­cess­ing. When com­pared to pre­vi­ous recipe used for the pre­sent LCLS cath­ode, the new recipe uses lower laser flu­ence and pro­vides faster emit­tance re­cov­ery. Laser point­ing sta­bil­ity is a key re­quire­ment for the suc­cess of the tech­nique. This paper pre­sents all de­tails of the stud­ies for four cath­odes with over a few tens of laser-as­sisted spots and com­pares the re­sults with the pre­sent LCLS cath­ode.