强流回旋加速器综合试验装置谐振腔关键高频参数的测量方法研究

A Shunt Impedance Measurement Method for CRM Cyclotron Cavity

射频谐振腔体的特征参数,包括谐振频率、品质因数和并联阻抗等,对加速器的物理设计和束流调试具有重要的参考意义,是衡量射频系统性能的重要指标。其中,等效并联阻抗的准确测量,是确定加速电压的峰值与分布的有效途径,其难点在于测量方法或对局部电磁场有扰动,或信噪比较低。论文通过应用研究的方法,由二端口无源网络散射参数的定义出发,设计了先进的测量方案,采用了特殊设计的阻抗探针,获得了强流回旋加速器综合试验装置的加速电压分布。同时使用同样的方法,对100 MeV回旋加速器金属实验腔体的电压分布进行了实验研究,该结果与三维计算机仿真结果对比,相对误差小于1%。

The characteristic parameters of the cyclotron cavity are crucial for both cyclotron design and commissioning. Among which, the resonance frequency, the quality factor and shunt impedance of the acceleration gap are the three key parameters when identifying a cyclotron RF system. An accurate shunt impedance measurement can lead to a very close estimation of the Dee voltage under giving driven power, includes both maximum quantity and distribution. The difficulties of such measurements are that either the probe will interfere local EM field, or have very limited signal to noise ratio. A new shunt impedance measurement method has been reported in the paper, starting with the definition of scatter parameter of passive network, followed with probe design, measurement setup and result of the CRM cyclotron cavity. Also, the same method has been applied in the measurement of 100 MeV cyclotron cavity, the result has been confirmed by the 3D RF structure computation code in this ease, and the difference is less than one percent.