Reemission of Ionically Pumped H2 and He from a Stainless Steel Surface

${\mathrm{H}}_2$ and He discharges in a stellarator produce copious wall bombardment by the plasma ions. The reemission rate of the gas was measured for times of 0.06 to ${10}^5$ see after bombardment. The rate was approximately proportional to $t^{\text{−0.6}}$ for He and $t^{\text{−0.75}}$ for ${\mathrm{H}}_2$ . The reemission is also calculated assuming diffusion of the gas in the solid and taking into account the finite nonuniform initial distribution. It follows from the analysis that the rate is proportional to $t^{\mathrm{-n}}$ where n approaches 0.5 or 1.5 as the ratio of reemission to bombarding time approaches zero or infinity.