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

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.