BEPC Ⅱ直线加速器数字BPM前端调理电路的研制

Development of digital BPM front-end conditioning circuit for BEPCⅡ linac

针对北京正负电子对撞机改造工程(BEPCⅡ)直线加速器束流位置测量电子学系统故障率上升这一现状,结合BEPCⅡ直线加速器束流参数以及BPM电子学ADC芯片带通采样的需求,设计了隔离度高、幅相一致性好的数字BPM射频前端电子学模块。数字BPM电子学系统采用MicroTCA 4.0系统架构,以FPGA作为主控制器,基于EDA软件开发设计。重点介绍了射频前端电子学模块中射频功率放大器、数字可调衰减器、带通滤波器等设计和实验室及在线测试结果。BEPCⅡ对撞模式下,使用正电子束流,完成电子学系统在线测试,x方向位置测量精度约为38.46μm,y方向位置测量精度约为26.16μm,其测量精度和系统稳定性优于商用模拟BPM电子学模块,能够满足BEPCⅡ直线加速器束流位置测量需求。

Aiming to control the rising failure rate of electronics system for BEPC Ⅱ linac’s beam position measurement, considering the physical design parameters of BEPC Ⅱ and the requirements of band-pass sampling of BPM electronics ADC chip, a digital BPM RF front-end electronics with high isolation degree and good amplitude and phase consistency is designed. The digital BPM electronics system adopts MicroTCA 4.0 system architecture, takes FPGA as the main controller, and is designed based on EDA software. This paper mainly introduces RF power amplifier, digital adjustable attenuator and bandpass filter in RF front-end electronics module, as well as the laboratory and online test results. In the collision mode of BEPC Ⅱ, positron beam was used to complete the electronic system online test, and the measurement accuracy of x-direction was about 38.46 μm, while that of y-direction was about 26.16 μm. The measurement accuracy and system stability of the proposed method are better than that of commercial analog BPM electronics module, and can meet the beam position measurement requirements of BEPC Ⅱ linac.