Kinetic model for hydrogen absorption in tungsten with coverage dependent surface mechanisms

Abstract

In this work, a kinetic model is presented to describe hydrogen absorption and desorption from tungsten at different surface coverages. Activation energies for hydrogen absorption into the bulk and desorption from the surface of tungsten are modelled by functions that depend explicitly and continuously on the hydrogen surface coverage. A steady-state model is developed to derive these activation energies from experimental data. The newly developed coverage dependent activation energies are then implemented in the non steady-state rate-equation code MHIMS. Published experimental results on D uptake and retention of self-damaged tungsten exposed to 0.28 eV deuterium atoms at different temperatures ranging from 450 K to 1000 K can be successfully described with this approach. Finally, the steady-state model is applied to determine surface concentration, bulk concentration and migration depths of hydrogen isotopes in tungsten exposed to various atomic fluxes and temperatures ranging from milder conditions in laboratory experiments to divertor strike point conditions in tokamaks.

Predictive Atomistic Model for Hydrogen Adsorption on Metal Surfaces: Comparison with Low-Energy Ion Beam Analysis on Tungsten

“…In the red region of Figure 8 where the surface is bare, the absorption energy is 1.5 eV and the recombination energy is 1.7eV. Such results can help establish a kinetic model of the surface, similar to the one recently developed by Hodille et al 11 .…”

“…These mechanisms are characterized by physical quantities that are mostly established via density functional theory (DFT) calculations. Today, current MRE models attempt to incorporate plausible surface mechanisms to improve their capability to reproduce as accurately as possible experimental TDS data. − However, what remains is the need to establish the coverage of the surface versus the experimental conditions to which it is exposed; this is precisely the aim of the present work.…”

Modelling tritium adsorption and desorption from tungsten dust particles with a surface kinetic model

“…In previous simulation studies, we took this into account by considering a continuous function E des (θ) with the following form [11]: For the DFT data from [12], the desorption energies are calculated with two methods: Nudge Elastic Band (NEB) or energy difference between adsorption state and gas state (emb). For the DFT data from [13], only the energy difference between adsorption state and gas state are reported.…”

Deuterium transport and retention in the bulk of tungsten containing helium: the effect of helium concentration and microstructure

“…We want to stress here that despite the fact that neither the fluxes nor the energies of our D atom beam resemble fluxes or energies expected for the DEMO first wall the above statement holds true. For expected particle fluxes in the range of 10 18 to 10 20 D/m 2 s [67,68] and wall temperatures up to 600 K retention is determined by the trap density and not the solute HI concentration [69]. Hence, our gentle atom loading procedure can directly be used to predict retention for the given temperature.…”

“…This does not hold true for higher temperatures that will prevail in the high heat flux areas of the divertor. At these temperatures retention is dominated by the balance between the HI influx and thermal de-trapping [69]. The retention values from figure 15 might therefore only be considered as lower limits.…”