For efficient FEL operation, we have developed a photocathode rf gun driven by a pulsed Nd: YAG laser. Since the timing of laser irradiation is crucial for stable photocathode operation, we investigated the effects of a timing jitter on the gun performance by using our simulation code. It was predicted that the timing jitter of laser irradiation should be less than ±2.5 ps in order to keep beam quality stable. The photocathode rf gun was installed in the rf linac system. With one signal generator for the laser (89.25 MHz) and the linac (2856 MHz), and afeedback system for the laser pulse timing of the laser oscillator, the jitter was successfully suppressed to be less than ± 2.5 ps. The electron beam characteristics were measured at the linac exit. It was confirmed that a heated metal photocathode (LaB6) provided sufficient beam brightness and a long lifetime. Compared to thermionic cathode operation, a significant improvement of the beam quality (Δ E/E-1%, Bn-1011 A/m2rad2) was achieved. These results could contribute to the improved FEL performance and other scientific and industrial applications.
