BEAM STABILIZATION IN THE SPring-8 LINAC

• Investigate the variation chains which result in beam instability The beam stability of the SPring-8 linac has been improved by means of reducing RF variations, providing beam energy compensation, and reinforcement of monitor systems: Variations in the RF power and phase have been reduced by improving the voltage regulation system for the klystron modulator, and by stabilizing the temperature drift of the atmosphere and cooling water in order to reduce the phase variation. These improvements realized a greatly reduced energy fluctuation of 0.03% rms. A new synchronous oscillator synchronizes a beam trigger pulse and a 2856 MHz reference signal. Variation in the beam charge was reduced by this synchronizing technique; the stabilized beam loading consequently resulted in the beam energy fluctuation of 0.01% rms. A beam energy compression system (ECS) was installed to compensate for accidental energy variation and reduce the energy spread due to beam loading. The reduced energy spread enabled the high-current injection without increasing beam loss. A BPM system employing shared memories for synchronized fast data acquisition has been constructed. A quasi nondistractive profile monitor using OTR was installed in a chicane section of the ECS to observe the beam energy and energy spread during the beam injection. These monitors greatly aid in both beam diagnosis and beam adjustment. • Fix origins of the variation chains • Synchronize the linac RF and the ring RF • Introduce an energy compression system (ECS) • Reinforce the monitor and control system The last item does not directly contribute the stabilization; however, it is quite important to maintain the stability during a long-term operation of the linac and the reappearance of the beam. In this paper, we describe only important devices of the monitor system. We have carried out this program step by step since 1998[2,3]. As a result, a minimum beam energy fluctuation of 0.01% rms has been achieved and the reduced energy spread has allowed realization of a highcurrent injection into the synchrotron. Present performance of the linac with an operation of the ECS is given in Table 1.