Temperature dependence of deuterium retention at displacement damage in tungsten

Abstract

Tritium retention at displacement damage will increase the tritium inventory in tungsten plasma-facing components in fusion reactors. However, the quantity retained strongly depends on the temperature of the material during exposure to the plasma. Here we examine how the temperature dependence of the various physical processes affects hydrogen isotope retention at damage in tungsten. Processes considered here are diffusion, precipitation of molecular D2 in internal voids, binding at traps and annealing of displacement damage. A conceptual model is presented which incorporates the effect of precipitation on D permeation and trapping. The model predicts that D retention at damage should be highest in a temperature range from about 200 °C to 400 °C. D retention is lower at T < 200 °C due to slow permeation, and lower at T > 500 °C due to weak binding to the traps.