Theoretical analysis of deuterium retention in tungsten plasma-facing components induced by various traps via thermal desorption spectroscopy

Abstract

Thermal desorption spectra (TDSP) reported in the literature and resulting from thermal desorption experiments performed on tungsten samples exposed to deuterium at several fluences are analyzed using a reaction-diffusion model including up to ten different types of traps. The use of a large number of types of traps allows accurate fits of TDSP at all fluences using a unique broad spectrum of detrapping energy. Detrapping energies found in this work are in good agreement with detrapping energies predicted by density functional theory when several hydrogen atoms are trapped in a single tungsten vacancy. The comparison between the distribution of deuterium concentrations in material and distribution of trapped deuterium concentrations in TDSP suggests that traps characterized by a broad spectrum of detrapping energy, which may correspond to tungsten vacancies, are predominantly located near the material surface (≲10 nm).

Surface coverage dependent mechanisms for the absorption and desorption of hydrogen from the W(1 1 0) and W(1 0 0) surfaces: a density functional theory investigation

“…Elastic Recoil Detection Analysis (ERDA) [21], Low Energy Ion Scattering (LEIS) and Direct Recoil Spectroscopy (DRS) [22][23][24] are also used, mostly to gain information on the surface properties. TDS can access global information related to the binding state of hydrogen in the bulk and on the surface, while ion beam analysis accesses local From the theoretical point of view, calculations and simulations have been carried out from the atomistic scales using Density Functional Theory (DFT) [24][25][26][27][28][29][30][31][32][33][34][35][36][37][38] and Molecular Dynamics (MD) [39][40][41][42][43], to the macroscopic scale using Kinetic Monte Carlo (KMC) [44][45][46][47] and Macroscopic Rate Equations (MRE) [15,[48][49][50][51][52][53][54][55][56][57][58][59][60]. Combining both these approaches results in the commonly called multi-scale approach, in which KMC [44,…”

“…Combining both these approaches results in the commonly called multi-scale approach, in which KMC [44,45] and MRE models are parametrized with available DFT data. But in most of the published KMC or MRE models, due to the lack of available DFT data, the surface processes for hydrogen are either neglected [49,[51][52][53][54][55][56]59] or considered in a simplified way with models making use of the recombination coefficient for hydrogen [15,48,58,60]. An accurate experimental value of the recombination coefficient is nevertheless unestablished due to large uncertainty from available measurements [61].…”

“…In tokamak, such recombination mechanisms have to be considered for detached regime of the plasma during which a high flux of neutrals impinges the surface.5.2.1 -Coverage dependent activation energiesTPD spectra are recorded on single-and poly-crystalline samples and their shape are well fitted by rate-equation models incorporating different sets of activation energies. Guterl et al[60]…”

Saturation of tungsten surfaces with hydrogen: A density functional theory study complemented by low energy ion scattering and direct recoil spectroscopy data

“…This topic is of high relevance to model the retention and release of hydrogen from tungsten. To this end, both thermodynamic 28,29,30,31 and kinetic 32,33,34,35,36,37 models built via DFT data exist, however, thus far surface effects have not yet been included with explicit physical ground. Both models aim to simulate and interpret experimental results, mostly from TDS 38 39 , 40 , 41 , 42 , 43 , 44 .…”

Experimental determination of the deuterium binding energy with vacancies in tungsten

“…Calculations of the hydrogen-defect interaction are often performed by using the density functional theory (DFT) [5][6][7][8][9][10][11]. Experimental investigations of the hydrogen-defect interaction are often performed by thermal desorption spectroscopy (TDS), and the parameters of the interaction are obtained by fitting numerical calculations based on diffusion-trapping codes to experimental thermal desorption spectra [3,4,[12][13][14][15][16][17]. Aside from the uncertainties of the thermal desorption measurements [18,19], a large uncertainty in the determination of characteristics of trapping sites in this approach is given by the fact that a result of a TDS spectrum simulation depends on many input parameters in the numerical model (H detrapping energy, H diffusivity in the material, trap concentration profile, initial distribution of trapped H, recombination rate at the surface).…”