屏蔽罩开启过程冷冻靶热辐射屏蔽方案研究

Study on Thermal Radiation Shield Schemes of Cryogenic Target During theThermal Shield Removal Process

在激光惯性约束核聚变的点火过程中,低温屏蔽罩的移除会使大量外界环境辐射进入冷冻靶,燃料靶丸温度场的变化直接影响燃料冰层的质量。针对六端直柱腔冷冻靶展开数值模拟研究,建立了多层热辐射屏蔽结构的三维全要素模型,基于Boussinesq假设和离散坐标辐射模型,研究了低温屏蔽罩的开启速度及不同热辐射屏蔽结构等因素对靶丸温度场特性的影响。结果表明:增大低温屏蔽罩的开启速度,会加快靶丸表面温度上升的速度,并缩短最大温差峰值出现的时间和温度场的稳定时间;采用辐射屏蔽片结构优于二级冷屏,能有效减少外界高温辐射热冲击的影响,可以使低温屏蔽罩开启后靶丸表面的温升降低44.3%,最大温差的峰值降低45.2%,温度场稳定所需的时间减少5.3%;提高屏蔽片的表面发射率,缩小屏蔽片与硅臂间的距离可以进一步降低屏蔽罩开启过程中靶丸表面的温升和温度场均匀性的恶化程度。研究结果可为冷冻靶固定式热辐射屏蔽结构方案的选择以及低温屏蔽罩开启过程靶丸表面温度场的控制提供理论指导。

In the process of laser inertial confinement fusion ignition,a large amount of external environment radiation enters the hohlraum with the cryogenic shield removed.As a result,the change in the surface temperature of the fuel capsule determines the quality of the fuel ice layer.In the present study,a three-dimensional model was established for a six-entrance cylinder-hohlraum cryogenic target with multiple thermal shields based on the Boussinesq hypothesis and the discrete coordinate radiation model.The effects of the moving speed of the cryogenic shield and the different thermal radiation shields on the temperature characteristics of the capsule were analyzed.The results show that increasing the moving speed of the cryogenic shield will accelerate the surface temperature rise of the capsule and shorten the peak time of the maximum temperature difference and the stability time of the temperature field.The fixed radiation slice is better than the secondary cryogenic shield,which can effectively reduce the thermal shock of the external environmental radiation.It can reduce the surface temperature rise of the capsule by 44.3%,the peak value of the maximum temperature difference by 45.2%,and the required stable time by 5.3%.Increasing the surface emissivity of the fixed radiation slice and reducing the distance between the fixed radiation slice and the silicon arm can further reduce the surface temperature rise and is favorable to the capsule temperature uniformity during the removal of the cryogenic shield.The results can provide theoretical guidance for the design and control of the thermal radiation shields of the cryogenic target.