Bunch length monitor using two-frequency analysis for rf gun system

An rms (root mean square) bunch length monitor for a laser-driven photocathode rf gun system based on a two-frequency analysis technique has been developed. Typically, the photoelectron beam generated from the rf gun system has an energy of 3-5 MeV and an rms bunch length smaller than 20 ps down to 3-4 ps. This monitor is suitable for such electron beam measurement. The rms bunch length as a function of rf phase was experimentally measured using both the rms bunch length monitor and streak camera technique using a 50 MeV electron beam at the KEK accelerator test facility (KEK-ATF) injector section which has an rf gun system and a 3-m-long accelerator structure. A numerical simulation study was also performed using the PARMELA code. The availability of this monitor was clearly verified by comparing the results. Consequently, this monitor was installed in the rf gun system at Waseda University and the rms bunch length measurement for a 3.5 MeV electron beam was precisely performed using the monitor.