Behavior of tungsten exposed to high fluences of low energy hydrogen isotopes

Tungsten is a candidate plasma facing material under investigation in a Sandia National Laboratories project conducted at Los Alamos National Laboratory. Samples of 99.95% tungsten provided by Plansee Aktiengesellschaft were exposed to 100 eV deuterium and tritium ions at a range of fluxes from 2.3×1017 to 1.3×1018 ions/cm2 s for one hour at 623 K in the tritium plasma experiment. The samples were outgassed to determine the amount of retained hydrogen isotopes. The retention scaled at slightly greater than the square root of the fluence. The fractional retention was on the order of 10−5. The data from these experiments were combined with previous results to construct a comprehensive model of the migration and retention behavior for hydrogen in tungsten. A second set of experiments involved exposing 99.95% tungsten foils provided by ÆSAR to 100 eV deuterons at a flux of 6×1017 D/cm2 s for 30 min at 423 and 373 K. Scanning Electron Microscopy analysis was performed on the samples to determine the effects of the plasma exposure. Unannealed samples revealed extensive blistering with many blister caps removed. Samples annealed to 1473 K showed minor blistering, and samples annealed to 1273 K showed no blistering. The SEM analysis was used in conjunction with the retention results to understand the role of annealing and defects in trapping within the tungsten.