Longitudinal Phase-Space Direct Measurement of Intermediate Pulses for a High-Intensity Beam Accumulation in the J-PARC RCS

Abstract The Japan Proton Accelerator Research Complex (J-PARC) 3 GeV rapid cycling synchrotron (RCS) accumulates a MW-class high-intensity proton beam. The RCS adopts a phase-space painting injection in both transverse and longitudinal planes during the multiturn injection to mitigate the space-charge force, which is a source of beam loss. In longitudinal painting injection, it is important to maintain the momentum of all pulsed beams injected from the linac. However, the momentum from the linac fluctuates due to beam loading induced by the high-intensity beam. The RCS requires a thinned time structure of the pulsed beam during injection to control the charge density of the accumulated beam. The momentum fluctuation increases as a result of the complicated time structure. In this study, we developed and evaluated a direct measurement system for the longitudinal phase-space (phase and momentum deviation) of all injected pulsed beams. Furthermore, the phase space under various operating conditions was measured, and an increase in momentum fluctuations due to beam loading under thinned beam conditions was clearly observed. This monitoring system is well suited for facilities accelerating beams with complex time structures, and it can significantly contribute to beam loss reduction.