Plasma–surface interaction in the context of ITER

Surface temperature effects on the dynamics of N2 Eley-Rideal recombination on W(100)

Quasiclassical trajectories simulations are performed to study the influence of surface temperature on the dynamics of a N atom colliding a N-preadsorbed W(100) surface under normal incidence. A generalized Langevin surface oscillator scheme is used to allow energy transfer between the nitrogen atoms and the surface. The influence of the surface temperature on the N(2) formed molecules via Eley-Rideal recombination is analyzed at T = 300, 800, and 1500 K. Ro-vibrational distributions of the N(2) molecules are only slightly affected by the presence of the thermal bath whereas kinetic energy is rather strongly decreased when going from a static surface model to a moving surface one. In terms of reactivity, the moving surface model leads to an increase of atomic trapping cross section yielding to an increase of the so-called hot atoms population and a decrease of the direct Eley-Rideal cross section. The energy exchange between the surface and the nitrogen atoms is semi-quantitatively interpreted by a simple binary collision model.

Scattering of hyperthermal nitrogen atoms from the Ag(111) surface

Measurements on scattering of hyperthermal N atoms from the Ag(111) surface at temperatures of 500, 600, and 730 K are presented. The scattered atoms have a two-component angular distribution. One of the N components is very broad. In contrast, scattered Ar atoms exhibit only a sharp, single-component angular distribution. There are noteworthy features in the angle-resolved energy of the scattered N when compared with Ar. Taking into account the relative masses involved, N atoms lose significantly more energy at the surface than Ar. However, there is a preferential loss mechanism that predominantly affects low-energy N atoms with small total scattering angle trajectories. The results are interpreted in terms of probing of different interaction potentials: strongly attractive and almost purely repulsive, and spin-state changes during the interaction of N with the surface appear probable.