CSNSⅡ真空差分系统设计

Differential Pumping System at CSNSⅡ

CSNSⅡ加速器束流打靶功率从100 kW升级至500 kW,要求直线加速器平均束流功率从5 kW提高到25 kW,脉冲束流强度从12.5 mA提高到大于40 mA,这必然导致直线段常温腔压力上升。差分系统作为常温段与超导段之间的重要匹配单元,其真空系统设计可以大幅降低此区间的压力,同时减少低能差分系统末端的残余气体成分,有效避免常温腔气源对超导腔性能造成影响。目前,直线末端(DTL腔)动态真空约为2.0×10^(-6)Pa,而CSNSⅡ超导腔前后的低能差分系统(LEDP)和高能差分系统(HEDP)动态真空均要求≤5.0×10^(-8)Pa。针对该问题,本文对LEDP和HEDP真空系统进行了系统设计,并通过搭建模拟系统和实验验证了设计的合理性。结果表明,实验结果与模拟结果基本吻合,采用离子泵与NEG泵组合的方案,可以满足LEDP和HEDP的真空需求,并有效减少LEDP末端的残余气体成分。

The power of the CSNSⅡaccelerator beam is upgraded from 100 kW to 500 kW,requiring that the average beam power of the linear accelerator to be increased from 5 kW to 25 kW,and the pulsed beam current to be increased from 12.5 mA to greater than 40 mA.This inevitably leads to an increase in the pressure of the room-temperature cavities.The differential pumping system,as a crucial matching unit between the room-temperature and superconducting segments,can significantly reduce the pressure distribution in this range,and reduce the residual gas components at the end of the LEDP to effectively avoid the impact on the performance of the superconducting cavities from gas sources in the room-temperature cavities.Currently,the dynamic pressure at the end of the linear section(DTL cavity)is approximately 2.0×10^(-6)Pa,while the low-energy differential pumping systems(LEDP)and high-energy differential pumping systems(HEDP)at the front and rear of CSNSⅡsuperconducting cavities,both require a dynamic pressure of≤5.0×10^(-8)Pa.This paper presented a systematic design of the vacuum systems for LEDP and HEDP,and simulation and experimental verification were carried out.The findings show that the experimental results are in basic agreement with the simulation results.The combination of ion pump and NEG pump can meet the vacuum requirements of LEDP and HEDP,and effectively reduce the residual gas composition at the end of LEDP.