J-PARC 3-GeV RCS: 1-MW beam operation and beyond

The J-PARC 3-GeV rapid cycling synchrotron (RCS) has recently achieved a 1-MW beam operation with considerably low fractional beam loss of a couple of 10−3 as a result of continuous efforts iterating experiments and numerical simulations. This success of the 1-MW beam operation opened a door to further beam power ramp-up beyond 1 MW; we are now promoting 1.2~1.5-MW-equivalent high-intensity beam tests looking ahead to future upgrades at J-PARC. In this article, we first review the current status of beam loss in the 1-MW beam operation, then presenting the recent results of the 1.2-MW beam tests with particular emphasis on our approaches to beam loss issues. The beam intensity limit of the RCS is also discussed with well-established numerical simulations.