A high power,broadband and rapid frequency sweeping RF system was developed to satisfy the demand of China Spallation Neutron Source (CSNS)rapid cycling synchrotron (RCS).The RF system mainly includes a ferrite loaded resonant cavity,a RF power source,a bias supply and a low level RF system.The repetition frequency is 25 Hz and the sweeping frequency range is 1.022-2.444 MHz.One cavity with two gaps can provide a maximum accelerating voltage of 30 kV.The tuning control of two stages can successfully solve the detuning problem during rapid frequency sweep-ing.The beam feed-forward and direct feedback can compensate the heavy beam loading effect.

The rapid cycling synchrotron（RCS） is part of the China Spallation Neutron Source（CSNS）. The RCS provides 1.6 Ge V protons with a repetition rate of 25 Hz. The RF system in RCS is mainly composed of a ferrite loaded RF cavity, a high power tetrode amplifier, a bias supply of 3300 A and a digital low level RF（LLRF） system based on FPGA. The major challenge of the LLRF system is to solve problems caused by rapid frequency sweeping and the heavy beam loading effect. A total of eight control loops are applied to ensure the normal operation. An effective feedforward scheme is widely used to improve the dynamic performance of the system. The design of the LLRF system and high power integration test results with the prototype RF system are presented.

给出了一种解决高带宽、高跟踪精度、大电流电源的方案,该方案结合开关电源与线性电源各自的优点,并在中国散裂中子源(CSNS)/快循环同步加速器(RCS)射频偏流源系统中得到了应用,满足了系统设计要求.

利用同轴线理论分析了扫频工作的中国散裂中子源(CSNS)铁氧体加载同轴谐振腔的主要性能参数.给出了铁氧体加载腔在三维电磁场仿真计算中的建模过程,在场分析的基础上提出了陶瓷介质等效谐振电容的方法.将模拟计算得到的腔体的谐振特性与同轴线理论计算和实际腔体测量结果相比较,三者吻合得非常好.通过对腔体样机母排引入的寄生模的实验和模拟研究,提出了解决寄生模问题的方法;通过对腔体内铁氧体环的填充系数的研究,给出了短尺寸腔的扫频工作方案.

As part of the international research program on the superconducting cavity for the International Linear Collider (ILC) R&D on the 1.3 GHz low loss superconducting cavities has been carried out at the Institute of High Energy Physics (IHEP) since 2005. A design of 1.3 GHz low loss cavity shape was proposed and six single-cell cavities of different niobium material were successfully fabricated with standard technology. In this study our priority was on large grain (LG) cavities. The two LG cavities were treated with complete procedures of surface treatments based on chemical polishing (CP) without electro polishing (EP) at IHEP. The two LG cavities and a fine grain cavity were sent to KEK for vertical testing. All the three cavities reached accelerating gradients higher than 35 MV/m and the maximum gradient of 40.27 MV/m was achieved in the LG cavity. This paper presents the process of the vertical RF tests and the comparison of the LG and fine grain cavities's performance.