Function of bunching segment in multi-cell RF gun

With a bunching segment and a shortened first cell, the 4+1/2 cell RF gun produced in CAEP has been proved experimentally to be effective in reducing electron back bombardment. The analysis of the electric field distribution and electron motion in bunching segment of multi cell RF gun is presented in this paper. The electron capture efficiency and electron trajectory with different initial phase are calculated using Runge-Kutta method. The function of the bunching segment is discussed. The calculated parameters of the 4+1/2 cell RF gun agree well with the experimental results.