Through the combination of laboratory experiments, computer simulations and dedicated ASDEX Upgrade experiments it was possible for the first time to describe this interaction quantitatively. The underlying physical picture is shown in the figure: The implantation of nitrogen into tungsten induces the formation of tungsten nitride. As nitrogen does not diffuse into the bulk material, the surface can only store a limited amount of nitrogen and excess nitrogen escapes back into the plasma. The combination of this newly established surface model with plasma transport calculations in the code WallDYN correctly describes the nitrogen balance in ASDEX Upgrade. The simulations reveal that the nitrogen balance is dominated by the storage of nitrogen in the surface.
With this work Gerd Meisl graduated at the TU München in January 2015.
G. Meisl et al., New J. Phys. 16, 093018 (2014),
G. Meisl et al., J. Nucl. Mater. 463 (2015) 668,