The rapid cycling synchrotron (RCS) of the J-PARC is a high-power pulsed proton driver aiming for a 1-MW beam power. The most important issues in realizing such a high-power beam operation are controlling and minimizing beam loss to maintain machine activations within permissible levels. In the RCS, numerical simulations played a vital role in isolating beam loss mechanisms and finding their solutions in combination with actual beam experiments; various ideas for beam loss mitigation were proposed with helps of the numerical simulations, and verified by experiments. As a result of such continuous efforts including several hardware improvements, we have recently accomplished a 1-MW beam acceleration with considerably low fractional beam loss of several 10−3. This report presents our beam dynamics approaches to beam loss issues that we faced in a series of high-intensity beam tests of up to 1 MW.
