Studies of dual-harmonic acceleration at CSNS- II

The Rapid Cycling Synchrotron RCS) of the China Spallation Neutron Source (CSNS) complex is designed to provide 1.56 × 10 13 protons per pulse (ppp) during the initial stage, and it is upgradeable to 3.12 × 10 13 ppp during the second stage and 6.24 × 10 13 ppp during the ultimate stage. The high beam intensity in the RCS requires alleviation of space charge effects to reduce beam losses, which is key in such high beam power accelerators. With higher intensities in the upgrading phases, a dual-harmonic RF system is planned to produce flat-topped bunches that are useful to reduce the space charge effects. We have studied different schemes to apply the dual-harmonic acceleration in CSNS- II, and have calculated the main parameters of the RF systems, which are presented in this paper.