Voltage control loop for rapid cycling synchrotron digital low-level RF control

Beam loss control is a key point in the design of high power facilities like the Rapid Cycling Synchrotron (RCS) of the China Spallation Neutron Source (CSNS). The patterns of the RF acceleration voltage, frequency and phase are the main factors to determine the longitudinal motion of beam and the beam loss level. Therefore, the low-level RF system (LLRF) control system of CSNS/RCS must be stable and precise. In this paper, the design of the LLRF control system of CSNS/RCS was presented, especially the voltage control loop. In the loop, the difference between the deteeted voltage and a pattern is fed to a PI compensation function, and the PI output controls the amplitude of the RF signal. Through the modeling and analysis of each part of the control loop, a proper PI controller design was