The analysis of beam stability and improvement of RF system at HUST THz-FEL by digital LLRF

Abstract

An SLAC-like Compact Linac installed on the HUST THz-FEL has been used as an injector to produce high power THz radiation. In order to produce the terahertz radiation with high monochromaticity and repeatability continuously, the beam parameters should be stabilized rigorously. Therefore, by using beam-dynamic calculation and simulation, the stability targets for RF system have been proposed on basis of analyzing the influence of RF jitter. Furthermore, to meet the requirements for the RF stability, a digital-LLRF control system has been designed, both the system stability and the response rate of the feedback loop has been enhanced by suitable PI coefficients. In experiments, the instability of the RF power fed into the accelerator have been measured. And an LLRF system based on FPGA has been constructed and added to present RF system. The preliminary measurement results show that the LLRF system is effective to suppress jitter and the targets of RF stability is achieved.