Hydrogen permeation behavior through tungsten deposition layer

Abstract

Understanding of hydrogen isotope behaviors in plasma-facing wall is important from viewpoints of fuel control and tritium safety. Tungsten (W) is a candidate material of plasma-facing components. In this study, hydrogen diffusion coefficient and hydrogen solubility constant in the W deposition layer formed by hydrogen plasma sputtering were obtained by gas-driven permeation experiments. The hydrogen diffusion coefficient in the W deposition layer was smaller than that in bulk W, and the hydrogen solubility constant was larger than that in bulk W. Then, hydrogen permeation behavior through the W deposition layer growing on nickel plate by hydrogen plasma sputtering was observed in the temperature range from 77 to 145 °C. Initially, the hydrogen permeation flux steeply increased but then gradually decreased with increasing the thickness of the deposition layer. From the analysis of the permeation behavior by TMAP code, the recombination coefficient on the surface of the deposition layer was evaluated. The obtained recombination coefficient was smaller than that on bulk W.