Longitudinal beam dynamic design of 500 kW beam power upgrade for CSNS-II RCS

Purpose The accelerator of the China Spallation Neutron Source (CSNS) consists of an 80 MeV H- linac and a 1.6 GeV rapid cycling synchrotron (RCS). The design beam power is 100 kW, which has been reached. In the upgrade project (CSNS-II), the beam power will be upgraded to 500 kW by increasing the linac energy to 300 MeV and adding a dual harmonic RF system in the RCS. In order to alleviate space charge effect and improve beam quality, the longitudinal beam dynamic of CSNS-II RCS dual harmonic RF system has been studied.
Methods According to the longitudinal beam dynamic characteristics of CSNS-II RCS at different acceleration stages, the longitudinal emittance, bunching factor, momentum filling factor and bunch length are studied and optimized in this paper.
Results and conclusions The optimized bunching factor is greatly improved, and the tune spread caused by space charge effect is greatly reduced in CSNS-II. With the suppressed space charge effects, the beam loss can be well controlled in CSNS-II RCS.