Digital low-level RF system for the infrared free-electron laser facility

Abstract

The infrared free-electron laser facility (IR-FEL) is a new free-electron oscillator user facility in the University of Science and Technology of China (USTC), which has come into user operation in September 2021. To get a low energy spread electron beam, we designed and fabricated a digital low-level radio frequency system (DLLRF) based on the MTCA.4 platform to monitor and control the microwave field. The simulation for RF system is implemented to estimate the feedback coefficients and analyze the influence of driving chain noise and measurement noise in this case. Beam tests show that the pulse-to-pulse PI feedback eliminates the slow drift effectively and improves the stability of the phase from 3.4° to 0.19° (RMS). The application of the PI-type feed-forward decreases intra-pulse ripples of phase from 5° to 1° (peak to peak).