Minimization of Beam Loss and Significant Improvement of Beam Quality at the J-PARC RCS Design Beam Power of 1 MW

Abstract

At the 3 GeV Rapid Cycling Synchrotron (RCS) of J-PARC, we have achieved a significant beam loss mitigation to minimize the machine activation for beam operation at the designed 1 MW beam power. This was accomplished through systematic numerical simulations and beam tests during 2000 to 2022. The uncontrolled beam loss caused by foil scattering of the circulating beam during multi-turn injection period was reduced by minimizing the injection beam size and also installing a smaller size stripper foil. Subsequently, the space charge effects and the associated beam losses at 1 MW were minimized by implementing several measures, such as correcting resonances, optimizing longitudinal and transverse injection paintings as well as betatron tunes at injection. The beam loss throughout the RCS including the collimator area was 80% reduced as compared to that of 1 MW trial operation in 2020. Consequently, the residual radiation throughout the RCS was considerably reduced, obtaining a one-order-of-magnitude reduction at the collimator area for achieving a stable operation at a record high of more than 98% availability.