Performance study of high current photo-cathode RF-gun with new laser system

For a sub-picosecond pump-and-probe-type radiation chemistry work, a new synchronized electron linac and laser system was installed in Nuclear Engineering Research Laboratory (NERL) of University of Tokyo. The new 0.3 TW laser system with a Ti:Sapphire oscillator (795 nm) and amplifiers generate 300 ps pulses at 10 Hz at first. The laser is splitted into the two beams. The first is compressed to 4 ∼ 11 ps so as to drive the RF-Gun and generate a pump-electron-beam. The second is compressed to 100 fs and used for the probe-light. The drive laser is converted to the third harmonics(265 nm, < 250 μJ). Moreover, a new 15 MW klystron was installed for the linac RF system. The RF power is divided to the gun and the accelerating section. Finally the time jitter between the pump-electron-beam and the probe-laser is designed to be 320 fs (rms). By using the new drive laser system, the charge of 7 nC per bunch was observed at the exit of the gun. Improvement of the vacuum in the gun < 10^{-9} Torr) is most effective to obtain such a high charge beam. After two and a half years operation of the gun, no degradation of QE has been found for the Cu photo-cathode.