Numerical Simulation Research On Temperature Control In Cryogenic Target Fabrication

The cryogenic target fabrication is a core technique to achieve ignition in the inertial confinement fusion. In this paper, in order to get smooth deuterium-tritium(DT) layer in the indirect drive target,β-layering is used to fabricate DT target. The key factor is how to control the uniformity of the target out-surface temperature distribution. Taking the Laser Magajoule(LMJ) of France as a prototype, we study some temperature control problems in the indirect drive target by a CFD code (Fluent) under two dimensional (2D) axi-symmetric models.The auxiliary heating mechanism is studied. The results show that to achieve the temperature uniformity of target out-surface, the temperature of the hohlraum wall should satisfy a given distribution. It needs to apply auxiliary heating to the outside wall of the hohlraum as the cooling process. Considering heat conduction and radiation transfer only, the temperature uniformity of ignition target can be obtained when the heaters around the outside wall of the hohlraum about 1.3mm above and below the mid-plane with 635W /m3heat flux.The effect of He-H2 gas natural convection heat transfer in the hohlraum on the target temperature distribution and corresponding solutions are studied. The numerical simulations show that when the He-H2 gas in the hohlraum is reaching a special pressure, the natural convection effect should be taken into account. In order to meet the uniformity requirement of ignition target, with the auxiliary heating method, we fragment the hohlraum into seven gas-divisions by polymer membranes. Then, in combination with the correct temperature of the cooling rings with a temperature difference of between the two rings, the temperature instability of the target out-surface can be reduced well, meeting the requirement of ignition.±0.5mKThe effects of target misalignment and capsule nonuniformity on the DT layer uniformity are studied. The results show that to control the nonuniformity of the DT inner-surface less than1μm, target misalignment from the center of the hohlraum on the axial axis must be less than 8.5μm, and the roughness of the capsule should be controlled in0.72μm. Meanwhile, in order to achieve the uniformity of target, it should avoid the error of radial departure prior.