CSNS/RCS中的阻抗和束流不稳定性

中国散裂中子源（CSNS）的快循环同步加速器（RCS）是一台强流质子加速器，其束流平均功率达到100 kW。在此强流加速器中，真空部件的阻抗是引起束流不稳定的主要原因，它严重限制了束流强度及品质。对CSNS/RCS设计中的各种真空部件阻抗进行了详细计算，并以计算结果为出发点，理论分析了各种不稳定性强弱，确定了各种不稳定性发生的阻抗阈值，为真空部件结构设计提供了参考。对比较严重的电阻壁阻抗，采用阻抗壁尾场模型进行跟踪模拟，得到不稳定性增长率与理论计算值符合较好。自然色品有助于束流稳定，加入自然色品后模拟，电阻壁不稳定性消失。

Impedances and beam instability in RCS/CSNS

The rapid cycling synchrotron of the China Spallation Neutron Source is a high intensity proton accelerator, with an average beam power of 100 kW. The collective effects caused by the coupling impedances from the vacuum components may be the limit to beam power. The impedances from various kinds of components were investigated and the impedance budgets were summarized. According to the summarized impedances, the thresholds for instability were estimated. Because of the serious instability from the resistive wall impedance, a simple resistive wall wake field model was used to track the bunch oscillation, and the growth rate was derived from simulation which was consistent with analysis. When the natural chromaticity which helps to stabilize the beam is considered in the simulation, the instability of resistive wall will disappear.