Development of a precise timing system for the ISIR L-BAND linac at Osaka university

We are developing a free electron laser (FEL) in the infrared region and also conducting Self-Amplified Spontaneous Emission (SASE) experiment in the same wavelength region using the L-band linear accelerator at the Institute of Scientific and Industrial Research (ISIR), Osaka University. In order to conduct such studies, a stable operation of the linac is critical, so that we have developed a highly precise and flexible timing system for a stable generation of the high intensity electron beam with the energy region of 10-30 MeV. In the timing system, a rubidium atomic clock producing 10 MHz rf signal is used as a time base for a synthesizer which is used as the master oscillator for generating the acceleration frequency of 1.3 GHz. The 1.3 GHz rf signal from the master oscillator is directly counted down to produce the clock signal of the timing system at 27 MHz and the four rf signals for the linac and laser used in the beam experiments. The start signal for the linac is precisely synchronized with the 27 MHz clock signal. To make an arbitrary delayed timing signal, a standard digital delay generator is used to make a gate signal for a GaAs rf switch, which slices out one of the 27 MHz clock pulses to generate the delayed timing signal. Any timing signal can be made at an interval of 37 ns and the timing jitter of the delayed signal is less than 2 ps (rms). We will report the new timing system and its performance in detail.