Simulation On Influence Of Temperature Field Of Spherical Hohlraum Cryogenic Target

Controlled nuclear fusion,as a clean energy source to solve the future energy crisis of mankind,is being studied by all countries.Laser inertial confinement fusion is one of the key technical approaches for controlled nuclear fusion.A frozen target with a uniform DT ice layer is the preferred target for inertial confinement fusion ignition.The preparation of the frozen target can be achieved by strictly controlling the thermal environment around the target,and then obtaining a relatively uniform temperature field,thereby obtaining a relatively uniform DT ice layer.Based on the comparison of the cylindrical cavity and the spherical cavity model,the structural model of the outer spherical ball is selected.In this paper,three-dimensional structure simulation is used,and the computational fluid dynamics software Fluent is used to systematically study the related factors affecting the temperature distribution of the target.By simulating the four materials of glass target,CH polymer target,Be(Cu)target and high density carbon(HDC)target,the temperature field around the target is related to the thermal conductivity of the material.The ablation layer with high thermal conductivity has a uniform temperature field distribution around the target;meanwhile,as the thickness of the ablation layer is thicker,the temperature difference between the outer surface of the target is smaller,and the uniformity of the surrounding temperature field is better.The direction of the assembly offset of the target is different for the frozen target.The radial offset will seriously affect the uniformity of the temperature field,while the upward shift in the axial direction will increase the uniformity of the temperature field.In order to obtain the influence of radiation-related factors on the temperature field distribution of the frozen target,the frozen cover system was analyzed by computer simulation according to the requirements of the temperature control of the frozen target.As the size of the reticle increases,the temperature difference around the temperature of the target increases,which is not conducive to the formation of a uniform temperature field.As the diameter of the incident window increases,the amount of radiation entering the black cavity increases,and the increased radiant heat destroys the temperature field of the target,which is not conducive to the formation of a uniform temperature field.Therefore,an appropriately sized freezer cover and window diameter are used to form a uniform temperature field.In order to offset the influence of natural convection on the temperature field of the frozen target,the regulation of the filling method in the black cavity,the cooling mode during the refrigeration process and the temperature compensation method were studied.The results show that the filling of He-gas pressure during the cooling process has a great influence on the temperature distribution on the target,and the temperature gradually decreases with the increase of gas pressure.The mixed filling gas with high proportion of helium can improve the uniformity of the surface temperature of the target.Compared with the fixed wall temperature,the temperature drift mode is beneficial to improve the uniformity of the temperature field.Compared with the sinusoidal wave disturbance,the cooling wall surface is oscillated by rectangular wave,and the amplitude of the target equatorial temperature fluctuates greatly and the uniformity is poor.Temperature compensation is used to suppress temperature non-uniformity caused by natural convection caused by gravity.When the temperature of the upper cold arm is constant and the temperature of the lower cold arm is changed,the maximum temperature difference of the outer surface of the target increases first and then increases with the increase of the temperature difference between the upper and lower cooling arms.