中国科学院近代物理研究所正在进行等离子体直接注入方案的研究,以便为重离子物理研究提供稳定可靠的高流强束流。由于工作频率较低,用于等离子体直接注入方案的RFQ腔体采用了适合于低频的四杆型结构。在完成束流动力学设计的前提下,研究了RFQ腔体支撑臂的各参数对并联阻抗的影响。由于突出电极之间存在着一定大小的电容,会对腔体的性能产生影响,为使腔体达到最优化的设计,进行了突出电极对并联阻抗及场平整性的影响的研究,并给出了突出电极的取值范围。

Due to its advantages at low frequency,a 4-rod radiofrequency quadrupole(RFQ) structure has been adopted for the RFQ cavity at the Institute of Modern Physics,Chinese Academy of Sciences,which works at 100 MHz and is used for the direct plasma injection scheme. After the beam dynamics design,the parameters of the stems of the cavity were optimized to obtain the maximum shunt impedance. The capacitance existing in the projecting electrodes will affect the properties of the cavity,therefore,the influence of the projecting electrodes should be taken into account. Their influence on shunt impedance and flatness of the 4-rod RFQ cavity was studied,and the results show that the influence on shunt impedance can be neglected but it can not be neglected on flatness. In addition,the length range of the elctrodes was presented for good flatness.