Thermal Loading of a Direct Drive Target in Rarefied Gas

In an inertial fusion energy (IFE) power plant, each fusion micro-explosion (~10 Hz) causes thermal and structural loads on the IFE reactor wall and driver optics. The loading on the wall must remain sufficiently low to ensure that economic and safety constraints are met. One proposed method for decreasing the intensity of the wall loading is to fill the reaction chamber with a gas, such as Xe, at low density. The gas will absorb much of the radiation and ion energy from the fusion event, and then slowly release it to the chamber wall. Unfortunately the protective gas introduces major heat loads on the direct drive target. The thermal loading of a target, during injection, largely determines the viability of that target upon reaching chamber center. Thus, the density of the gas must be carefully selected to ensure that a target will survive injection. The objective of this work is to quantify and characterize the heat flux resulting from the interaction of the target and the protective gas. The loading of the target is modeled using DS2V, a commercial DSMC program. Using DS2V, this work explores the effect of the protective gas density, temperature, sticking (condensation) and accommodation coefficients on the heat flux to the target.