Dynamics of Hydrogenic Retention, Diffusion, and Trapping in Molybdenum

Hydrogenic retention, diffusion and trapping in plasma-facing components (PFC) are of great importance when examining wall fuelling and tritium retention issues for ITER. The Alcator C-Mod tokamak uses molybdenum for their PFC material, covered with boron films from regular boronizations. After cleaning the interior of the machine, Alcator C-Mod had purely Mo tiles. In the following shots, over 50{\%} of the injected deuterium was not recovered and thought to be lost in the walls. Repeated shots showed no signs of this ``wall pumping'' becoming saturated. This unexpected behaviour could have severe consequences for tritium retention in ITER, which is considering refractory metal tungsten PFC. The dynamics of D retention and diffusion must be resolved to understand these issues in pulsed tokamaks. The C-Mod tiles, deuterium-implanted Mo samples provided by the PISCES experiment at University of California-San Diego, and pure Mo samples will be studied using the DIONISOS experiment at the University of Wisconsin-Madison. Ion beam analysis will be used to investigate the dynamics of plasma-driven implantation and diffusion of deuterium in molybdenum as a function of plasma density, sample bias, surface temperature, and time.