Roughness Tolerance Studies for the Undulator Beam Pipe Chamber of   LCLS-II
  We investigate the effect of wall roughness on the wakefield-induced energy variation in the undulator beam pipe of LCLS-II. We find that a wall roughness equivalent to an rms surface slope of 30 mr increases the total induced energy variation within the bunch (due to the resistive wall wake) by a modest 20%. 
K. Bane and G. Stupakov
physics.acc-ph