Beam commissioning and beam loss control for CSNS accelerators

The China Spallation Neutron Source (CSNS) accelerators consist of an 80 MeV H- linac and a 1.6 GeV proton rapid cycling synchrotron (RCS), which provides 1.6 GeV proton beam to the target at a repetition rate of 25 Hz. The beam commissioning of CSNS accelerators had been started since April 2017, and to the end of February 2020, the CSNS reached the design beam power of 100 kW. The most important issue in high-power beam commissioning is the beam loss control, as well as the control of induced activities, to meet the requirement of manual maintenance. A series of beam loss optimization work had been done to reduce the uncontrolled beam loss. Transverse and longitudinal matching in the MEBT was performed. For RCS commissioning, the orbit and lattice correction, the matching between the rf frequency and the dipole field, the tuning of the injection beam were performed. Many efforts have beam made to depress the effects of space charge and collective instability for beam loss control, such as injection optimization, longitudinal beam dynamics optimization, tune optimization. The beam commissioning procedure and results for CSNS accelerators are introduced in this paper.