Modelling deuterium release during thermal desorption of D+-irradiated tungsten

Thermal desorption profiles were modelled based on SIMS measurements of implantation profiles and using the multi-trap diffusion code TMAP7 [G.R. Longhurst, TMAP7: Tritium Migration Analysis Program, User Manual, Idaho National Laboratory, INEEL/EXT-04-02352 (2004)]. The thermal desorption profiles were the result of 500eV/D+ irradiations on single crystal tungsten at 300 and 500K to fluences of 1022–1024D+/m2. SIMS depth profiling was performed after irradiation to obtain the distribution of trapped D within the top 60nm of the surface. Thermal desorption spectroscopy (TDS) was performed subsequently to obtain desorption profiles and to extract the total trapped D inventory. The SIMS profiles were calibrated to give D concentrations. To account for the total trapped D inventory measured by TDS, SIMS depth distributions were used in the near-surface (surface to 30nm), NRA measurements [V.Kh. Alimov, J. Roth, M. Mayer, J. Nucl. Mater. 337–339 (2005) 619] were used in the range 1–7μm, and a linear drop in the D distribution was assumed in the intermediate sub-surface region (∼30nm to 1μm). Traps were assumed to be saturated so that the D distribution also represented the trap distribution. Three trap energies, 1.07±0.03, 1.34±0.03 and 2.1±0.05eV were required to model the 520, 640 and 900K desorption peaks, respectively. The 1.34 and 1.07eV traps correspond to trapping of a first and second D atom at a vacancy, respectively, while the 2.1eV trap corresponds to atomic D trapping at a void. A fourth trap energy of 0.65eV was used to fit the 400K desorption peak observed by Quastel et al. [A.D. Quastel, J.W. Davis, A.A. Haasz, R.G. Macaulay-Newcombe, J. Nucl. Mater. 359 (2006) 8].