ORBIT Simulation, Measurement and Mitigation of Transverse Beam Instability in the Presence of Strong Space Charge in the 3-GeV RCS OF J-PARC

The transverse impedance of eight extraction pulse kicker magnets (KM) is a strong beam instability source in the 3-GeV RCS (Rapid Cycling Synchrotron) at J-PARC (Japan Proton Accelerator Research Complex). Significant beam instability occurs even at a half of the designed 1 MW beam power when the chromaticity (xi) is fully corrected for the entire acceleration cycle up to 3 GeV, but no beam instability occurs if the xi is fully corrected only at the injection energy of 0.4 GeV. To realize the designed 1 MW beam power, collective beam dynamics with including the space charge effect for the coupled bunch instabilities excited by the KM impedance and associated measures were studied by incorporating all realistic time-dependent machine parameters in the ORBIT 3-D particle tracking code. The simulation results for systematic beam instability studies and its mitigation measures were found to be very consistent with measurements and, as a consequence, an acceleration of 1 MW beam power has been successfully achieved.