Digital low-level RF control system for high intensity proton RFQ accelerator

The resonant frequency of the high intensity proton RFQ accelerator at the Institute of High Energy Physics is 352.2 MHz, and the control precision of the accelerating field is ±1% in amplitude and ±1° in phase, respectively. In order to accomplish these requirements, a digital low-level RF(LLRF) control system is adopted. This system includes three parts: the accelerating field amplitude and phase control, the cavity resonant frequency control and the high power interlock protection. The down-conversion of the cavity sampling signal and the up-conversion of the feedback excitation signal are realized by the analog devices. The real time feedback control of amplitude and phase adopts digital I/Q demodulation, and is assembled in a FPGA block, where three DSP blocks are used for communic