The compensation for the edge focusing of chicane bump magnets by harmonic injection in CSNS/RCS

In the Rapid Cycling Synchrotron(RCS) of China Spallation Neutron Source(CSNS), transverse painting injection is employed to suppress the space-charge effects. The beta-beating caused by edge focusing of the injection bump magnets leads to tune shift and shrinkage of the acceptance, which may result in additional beam loss. In RCS, the main quadrupoles are excited by White resonant power supplies, and the exciting current cannot be arbitrarily programed. Generally, this kind of perturbation could be corrected by trim-quadrupole, however, we don't have trim-quadrupole in CSNS/RCS. A new method based on the harmonic injection is firstly introduced to compensate the beta-beating caused by edge focusing of the chicane bump magnets at RCS. In this paper, the principle and feasibility of compensation scheme were presented. The simulation study was done on the application of the new method to the CSNS/RCS, and the results show the validity and effectiveness of the method.