Effects of atomic processes on fuel pellet ablation in a thermonuclear plasma

Abstract

The neutral-ablation model describing ablation of solid hydrogen fuel pellets in thermo-nuclear plasmas has been extended to determine the species composition of the ablatant consistent with the fluid profiles, and has been used to assess pellet shielding mechanisms. Aside from neutral-ablation shielding, none of the shielding mechanisms studied is very effective. Dissociation of hydrogen molecules extends pellet lifetimes by 10-20%. Ionization reduces the temperatures in the ablation by about a factor of three, but extends pellet lifetimes by only a few per cent. Excitation of atoms is not important because the fraction of excited atoms does not exceed a few per cent anywhere in the ablation. Bremsstrahlung and recombination radiation are negligible energy losses. Where emitted abundantly, line radiation is trapped within the optically thick ablatant. Incident electron heat is reduced by less than 10% in overcoming the electric potential of the pellet. Magnetic shielding is treated elsewhere.