CSNS漂移管直线加速器漂移管外壳冷却分析

Cooling Analysis of the Drift Tube Shell for Drift Tube Linac of China Spallation Neutron Source

摘要: 中国散裂中子源(China Spallation Neutron Source, CSNS)漂移管直线加速器(Drift Tube Linac, DTL)由4台9米长腔筒、161台漂移管及其他高频部件构成，负责把负H离子由3 MeV加速到80 MeV。漂移管外壳采用全无氧铜电子束焊接而成，壳内有独立的不锈钢水套，外壳和水套采用间隙装配，其间有约0.2 mm间隙填充环氧介质。外壳的高频热功率约200 W，为了降低外壳温度及减小失谐量，冷却十分重要，外壳靠水套冷却，冷却效果不仅与0.2 mm间隙介质的导热系数有关，还与水套的冷却换热系数有关。利用3D软件Workbench仿真分析间隙介质导热系数和水套冷却换热系数对漂移管外壳温度的影响，间隙介质的导热系数大于0.1 W∙m⁻¹∙℃⁻¹时，冷却效果较好且外壳温度随介质导热系数变化不大，介质导热系数小于0.1 W∙m⁻¹∙℃⁻¹时，随着导热系数的减小，外壳的温度会急剧升高，因此选择导热系数在0.2 W∙m⁻¹∙℃⁻¹以上的环氧树脂填充间隙，另外，为了达到较好的冷却效果，水套中的冷却水应该处于湍流状态，流量应大于1.8 L/min，冷却换热系数大于5500 W∙m⁻²∙℃⁻¹，漂移管实际运行中水套流量选择4 L/min，冷却换热系数约为10,000 W∙m⁻²∙℃⁻¹，外壳温度较低，失谐量较小，运行具有较高的可靠性和稳定性。

Abstract: Drift Tube Linac (DTL) which can provide energy gain from 3 MeV to 80 MeV is used in China Spalla-tion Neutron Source (CSNS), the DTL consists of 4 9 m-long cavities, 161 drift tubes and other com-ponents. The drift tube shell is made of oxygen free copper and welded by electron beam welding (EBW), there is an independent water jacket which has been assembled with about 0.2 mm clear-ance in the shell for cooling, the clearance is filled with epoxy. Under the 200 W high frequency thermal power, the cooling of drift tube shell is very important for reducing shell temperature and detuning. The shell temperature is not only related to the thermal conductivity of the 0.2 mm clearance medium, but also related to the heat transfer coefficient of the water jacket. With 3D code Workbench, the influence of thermal conductivity of the gap medium and heat transfer coefficient of the water jacket on the drift tube shell temperature is analyzed. When the thermal conductivity of the medium is greater than 0.1 W∙m⁻¹∙˚C⁻¹, the cooling effect is good, and the shell temperature does not change with the thermal conductivity of the medium, otherwise, the temperature of the shell will rise sharply with the decrease of the thermal conductivity. Therefore, the epoxy resin with the thermal conductivity above 0.2 W∙m⁻¹∙˚C⁻¹ is selected to fill the clearance. Moreover, in order to achieve better cooling effect, the cooling water in the water jacket should be in turbulent state, the flow rate should be greater than 1.8 L/min, and the heat transfer coefficient should be greater than 5500 W∙m⁻²∙˚C⁻¹. In actual operation, the flow rate of the water jacket is 4 L/min, and the heat transfer coefficient is about 10,000 W∙m⁻²∙˚C⁻¹. The drift tube shell temperature and detuning keep low and operating under high reliability and stability.