Modelling diffusion processes of deuterium in tungsten
Summary
The diffusion processes in tungsten are simulated by using Monte Carlo methods. Measurements of deuterium retention in tungsten are compared to theory. The influence of traps on deuterium retention is investigated. While simulating the atomic structure of tungsten takes a lot of calculation time, a method is introduced that is able to extend the total time that is simulated to weeks. To reach these timescales, the simple diffusion process is treated different than trapping and detrapping. The influence of traps on diffusion processes is demonstrated. Namely, if trap influence is neglected the observed retention behaviour cannot be recreated. Deep traps with trap energies around 1.2 eV keep deuterium trapped for large timescales at room temperature and they have a large effect on diffusion processes. However, it is very unlikely that they fully account for the observed behaviour of deuterium retention. Shallow traps with trap energies around 0.7 eV are shown to slow down diffusion, predicting behaviour that is in accordance with measurements.