L. Wang, A. Brachmann, F.-J. Decker, Z. Li, T.O. Raubenheimer, J.F. Schmerge, and F. Zhou,
   "Cathode Ion Bombardment in LCLS and LCLS-II RF Gun",
   in Proc. 37th International Free Electron Laser Conference, Daejeon, Republic of Korea, August 2015, paper TUP072, pp. 534-539,
    ISBN: 978-3-95450-134-2,
    doi:10.18429/JACoW-FEL2015-TUP072,
    http://accelconf.web.cern.ch/AccelConf/FEL2015/papers/tup072.pdf, 2015.