  The rapid cycling synchrotron (RCS) is part of China Spallation Neutron
Source (CSNS). The RCS provides 1.6GeV protons with a repetition rate of 25Hz.
The RF system in RCS is mainly composed of a ferrite loaded RF cavity, a high
power tetrode amplifier, a bias supply of 3300A and a digital low level RF
(LLRF) system based on FPGA. The major challenge of the LLRF system is to solve
problems caused by rapid frequency sweeping and heavy beam loading effect. This
paper will present the design and structure of the LLRF system, and show
results of performance tests.
