Stability of the RF system at the SPring-8 linac

The stability of the beam energy and energy spread at both the 1-GeV S-band linac and the 8-GeV synchrotron ring are crucial factors for determining the injection time for the storage ring. Since the linac has a lot of high-power RF equipment, any drift of the output power and phase from the various type of RF equipment will affect the beam energy in beam operation. We measured the output power and phase stability for many types of RF equipment. In order to investigate the drift of the RF parameters in the klystrons, which can be influenced by outside factors, the cooling water temperature and the environmental temperature were also measured. It turns out that the phase of klystrons coincide with the cooling water temperature drift. Although controlled by an air conditioning, the room temperature can vary about 4.0°C in the course of a day, affecting the high-power klystron drive system. After improvements of the air conditioning control system and the cooling water system for the klystron cavities, a beam current stability was reduced to 0.7% (1σ) from 9.0% (1σ) in beam operation