Internal energy distributions of BeH, BeD, and BeT molecules created during chemically assisted physical sputtering in JET tokamak plasma

Abstract

We present here the results of the spectroscopic analysis of the high-resolution visible spectra of beryllium hydride and its isotopologues (BeH, BeD, and BeT), produced during plasma–surface interactions during limiter and divertor JET-ILW (ITER-like Wall) pulses. The hydride production, being an important part of the wall erosion via chemical-assisted physical sputtering, shows visible dependence on plasma and wall conditions, and also on the isotope content of the plasma. This work shows that this dependence is also true for the molecular energy distributions, parameterized by rotational and vibrational temperatures. During the increase in the vessel wall temperature by 350 K, with constant plasma parameters, rotational temperature of the excited BeD molecules increases by 500 K, whereas the vibrational temperature decreases by 400 K. Another experiment was the scan of the integrated edge density, during which electron density increases with the increasing edge density, and electron temperature decreases. During that scan for BeD, Trot decreases by 300 K and Tvib by 400 K over the change in an integrated edge density of ΔNe=+8×1018 m−2. Both trends were compared with the trends in other isotopes, and the qualitative results are similar, but the limited data available restrict the possibility of a full quantitative comparison. To simplify the comparison between the results presented here and other experiments or modeling data, and also to check the comparability of the pulses performed in different isotopes, the Be ion line ratios are used as benchmarks of the edge plasma condition.