Synchronization between the laser and electron beam in a photocathode RF gun

The chemical reactions of hot or room temperature and/or critical water in a time-range of picosecond and sub-picoseconds have been carried out by the 18 MeV S-band linac and a Mg photocathode RF gun with the irradiation of third harmonic Ti: Sapphire laser, at Nuclear Engineering Research Laboratory (NERL), the University of Tokyo. Although this short bunch and 100 fs laser light are enough to perform the experiment of radiation chemistry in the time-range of sub-picoseconds, the total time-resolution become worse by the instability of synchronization between laser and radio frequency of linac. We found that the fluctuation of room temperature causes the instability, particularly the cycle of turning on/off of the air-conditioner. When we decrease the fraction of the room temperature within 0.1 degrees, the timing drift in an hour reaches 600 fs, closed to the timing jitter of 340fs than previous results.