Simulations of high-brightness RF photocathode guns for LLNL-SLAC-LBL 1 GeV test experiment

An ideal RF photocathode gun in a π-mode configuration supporting only a single mode with no nonlinear RF field is studied numerically with the simulation code PARMELA. For a given electron bunch, the normalized emittance can be minimized. Both the minimal normalized emittance and the optimized accelerating field are proportional to the square root of the peak current. Three possible RF photocathode guns for the LLNL-SLAC-LBL 1-GeV test are simulated. The results show that both a 2-ps and a 6-ps half-width bunch with 8-17-mm-mrad emittance and 1-nC charge per bunch can be generated by guns with (1) f=1269 MHz, E₀=30 MV/m; (2) f=1269 MHz, E₀=60 MV/m; and (3) f=2856 MHz, E₀=60 MV/m. Here, f is the RF frequency and E₀ is the peak accelerating field