Multiscale investigation of deuterium outgassing and plasma coupling in titanium deuteride electrodes

Abstract: Deuterium supply from a titanium deuteride cathode depends on how rapidly atoms move through the material and how the surface changes during a discharge. We combine molecular dynamics and finite-element simulations to examine these processes under prescribed thermal and pressure loads representing a cathode spot. The diffusion activation energies are 0.52 ± 0.03 eV for TiD2 and 0.11 ± 0.02 eV for TiD, the TiD1.5 series gives 0.604 eV with a prefactor of 1.71 × 10-6 m2 s-1. In TiD1.5, deuterium becomes increasingly disordered at 800-1000 K while the titanium framework remains largely ordered. Local heating melts the surface, after which pressure drives the liquid outward and produces a central crater with raised edges. The characteristic crater depth and diameter are approximately 1 and 3 μm, respectively. At 50 ns, a deuterium-depleted layer about 0.2 μm thick remains beneath the receded surface. The calculated release increases with pressure and amounts to approximately (1.5 -3.5) × 10-13 mol of atomic deuterium per spot. A separate diffusion calculation with closed boundaries gives surface half-recovery times of approximately 77 s at 300 K and 0.65 ms at 600 K. These results relate the deuterium available to a subsequent discharge to both surface erosion and redistribution within the remaining cathode. The release and recovery estimates apply to the loading and boundary conditions considered here.