强流质子RFQ加速器加速场的频率为352.2 MHz,加速场幅度和相位的精度分别要求控制在±1%和±1°的范围,为了达到这一要求,设计了一套数字低电平控制系统,该系统包括加速场的幅度和相位控制、腔体的谐振频率控制和高功率射频连锁保护3个部分。腔体采样信号的下变频及反馈激励信号的上变频由模拟器件来完成。幅相实时反馈处理过程采用数字I/Q解调的方法,在1块stratixⅡ的FPGA板上实现,板上另有3块DSP用于通信和协助FPGA进行数据处理。系统完成后与RFQ加速器进行联机调试,测试结果基本满足控制精度的要求。

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 communication and cooperate the FPGA to process data. The online debugging result satisfies the requirements of the control precision.