摘要: 中国科学院近代物理研究所在CSR-LINAC项目中设计了一台108.48 MHz的IH型RFQ直线加速器。该RFQ可以将质荷比为3~7的离子从4 keV/u加速到300 keV/u。在完成束流动力学设计的基础上，主要针对RFQ腔体的高频电磁设计展开了研究，同时利用了电磁场仿真和束流动力学模拟来研究腔体的四极场不平整度和二极场及其动力学影响。未经调谐的情况下，腔体的谐振频率为108.15 MHz，腔体空载品质因子Q₀为5 910，腔体功耗为123 kW。通过在支撑板两端增加底切的设计，将腔体的四极场不平整度由-21%~ 12%优化至±2.5%，满足了束流动力学要求。腔体的二极场为-3%~ -2.2%，使得束流在垂直方向小幅振荡，RFQ的垂直方向接受度减小5%。为了保证功率馈入时反射较小，将耦合器设置在临界耦合状态，耦合面积为940 mm²。为了补偿腔体的频率偏差和漂移，设计了调谐量分别为707和132 kHz的固定调谐器和可动调谐器。


The 108.48 MHz IH type RFQ for CSR-LINAC project is under design at Institute of Modern Physics, Chinese Academy of Sciences. This RFQ can accelerate heavy ions with mass to charge ratio of 3~7 from 4 keV/u to 300 keV/u. According to the beam dynamics requirement, the RF structure design has been finished. The quadrupole field unflatness and dipole field of the cavity were studied by electromagnetic simulation and beam dynamics simulation. The frequency of the cavity without tuning is 108.15 MHz, the Q₀ of the cavity is 5910, and the RF power loss is 123 kW. The quadrupole field unflatness of ±2.5%,which was -21%~12% before optimizing, is achieved to meet dynamics requirement through the undercuts in cavity supporters. The dipole field of -3%~ -2.2% causes the oscillation of the beam center and acceptance reduction of 5%. The power coupler must be in critical coupling state with the coupling area of 940 mm² for minimum reflection coefficient. The tuners, consist of coarse and fine tuners with frequency shift of 707 and 132 kHz respectively, is used for tuning of frequency deviation of the cavity.