Technical Issues on the Control of Plasma-Wall Interactions in Steady-State Magnetic Fusion Devices. 2. Plasma Wall Interactions Database and Related Computer Codes. Modeling of Hydrogen Isotope Recycling from Graphite, and the Data Needs for Diffusion and Recombination Coefficients.

Abstract

For the purpose of evaluating transient recycling of hydrogen at plasma-facing materials, mass balance equations for mobile and trapped hydrogen atoms have been proposed, in which the elementary processes leading to re-emission, such as diffusion, detrapping, (re)trapping, and local molecular recombination are taken into account. Under appropriate conditions, it was demonstrated that the concentrations of mobile and trapped species can be analytically solved as functions of depth, time, or ion flux, and that the thermal desorption spectrum can be calculated from the time dependence of the concentration of trapped hydrogen atoms. It was also shown that by using the analytical solutions, the diffusion constant and the rate constant of effective local molecular recombinations can be determined experimentally. The experimental data on the diffusion coefficient and the molecular recombination rate are summarized and critically discussed using the solution of the mass balance equations.