基于FPGA的电子直线加速器低电平系统前馈功能的实现  

Implementation of FPGA-based feedforward function in LLRF system for electron LINAC

作　　者：李松[1,2] 张俊强[1] 张猛[1] 赵明华[1] 

机构地区：[1]中国科学院上海应用物理研究所嘉定园区,上海201800 [2]中国科学院大学,北京100049

出　　处：《核技术》2016年第7期55-61,共7页Nuclear Techniques

基　　金：中国科学院战略性先导科技专项(No.XDA02010100)资助~~

摘　　要：用于驱动光中子源装置(TMSR Photo-Neutron Source Phase1,TDSN1)的15 Me V直线加速器,由于腔体中瞬态束流负载效应的存在使得束团在经过腔体后头部的能量过高,会导致束流能散变大,降低了束流的传输效率。"数字前馈补偿"方法在原有的数字低电平控制系统的现场可编程逻辑门阵列(Field Programmable Gate Array,FPGA)中加入前馈模块,通过直接削弱输入腔体的射频场的头部场强来达到降低束团头部能量的目的。实际数据表明,低电平系统前馈功能工作稳定,束流能散降低,束流的传输效率显著变高,克服了传统束流补偿法不能在大束团、高流强模式下工作的缺陷。Background： Due to the existence of transient beam loading effect in cavity, the energy of the bunch head is higher than the other part in 15-MeV linear accelerator （LINAC） designed for thorium molten salt reactor （TMSR） photo-neutron source. This uneven distribution of energy leads to high energy spread, thus depresses transmission efficiency of beam. Purpose： This study aims to develop a digital feedforward compensation to reduce the influence of beam loading effect and decrease energy spread of the beam. Methods： The Field Programmable Gate Array （FPGA） programming language VHDL （Very-High-Speed Integrated Circuit Hardware Description Language） was used to design the feedforward module. This module was added to the original FPGA modules of low level radio frequency （LLRF） control system to cut down the intensity of head of radio frequency （RF） field. Results： The experimental test shows that the feedforward function of LLRF control system suppressed the energy spread to an ideal level and the transmission efficiency of the beam current had also been significantly improved. Conclusion： The digital feedforward method overcomes the deflection of traditional beam compensation method which malfunctions in the situation of big bunch and high beam current.

关 键 词：现场可编程逻辑门阵列 先进先出电路 串行转换 前馈控制 低电平 直线加速器 

分 类 号：TL53[核科学技术—核技术及应用]