• L. Liu, J. Qiu, J. Tang, T. Wei
  IHEP Beijing, Beijing

China Spallation Neutron Source (CSNS) is a high power proton accelerator-based facility. Uncontrolled beam loss is a major concern in designing the high power proton accelerators to control the radio-activation level. For the Rapid Cycling Synchrotron (RCS) of the CSNS, the repetition frequency is too high for the longitudinal motion to be fully adiabatic. Significant beam loss happens during the RF capture and initial acceleration. To reduce the longitudinal beam loss, phase space painting is used in the RCS injection. This paper presents detailed simulation studies on the longitudinal motion in the RCS by using the ORBIT code, which include different beam chopping factors, momentum offsets, injection times and RF voltage patterns. With a trade-off between the longitudinal beam loss and transverse incoherent tune shift that will also result in beam losses, optimized longitudinal painting schemes are obtained.