Ion-kinetic simulation of D-3He gas-filled ICF target implosions with moderate to large Knudsen number

Experiments designed to investigate the transition to non-collisional behavior in D3He-gas ICF target implo- sions display increasingly large discrepancies with respect to simulations by standard hydrodynamics codes as the expected ion mean-free-paths λc increase with respect to the target radius R (i.e. when the Knudsen number NK = λc/R grows). To take properly into account large NK’s, multi-ion-species Vlasov-Fokker- Planck computations of the inner gas in those capsules have been performed, for two different values of NK, one moderate and one large. The results, including nuclear yield, reactivity-weighted ion temperatures, nu- clear emissivities and surface brightness, have been compared with experimental data and with the results of hydrodynamical simulations, some of which include an ad-hoc modeling of kinetic effects. The experimental results are quite accurately rendered by the kinetic calculations in the smaller-NK case, much better than by the hydrodynamical calculations. The kinetic effects at play in that case are thus correctly understood. However, in the higher-NK case, the agreement is much worse. The remaining discrepancies are shown to arise from kinetic phenomena (e.g., inter-species diffusion) occurring at the gas-pusher interface, which should be investigated in future work.