Erlangen 2018 – scientific programme
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P: Fachverband Plasmaphysik
P 18: Plasma Wall Interaction I - Poster
P 18.1: Poster
Wednesday, March 7, 2018, 16:15–18:15, Zelt Ost
Investigation of ground state excitation of sputtered tungsten in the linear plasma device PSI-2 — •Stephan Ertmer, Oleksandr Marchuk, Albrecht Pospieszczyk, Arkadi Kreter, and Sebastijan Brezinsek — Forschungszentrum Jülich GmbH - Institut für Energie- und Klimaforschung - Plasmaphysik, Partner of the Trilateral Euregio Cluster (TEC), 52425 Jülich, Germany
Tungsten (W) is foreseen as plasma-facing material in future fusion reactors. Spectroscopy is an important tool for particle flux measurements into the plasma. For the interpretation of the measured W line intensities the population distribution of J levels within the fivefold ground term 5D and the 7S3 level of sputtered tungsten released and entering the plasma remains an open question. A local thermal equilibrium (LTE) for these levels with an effective temperature in the order of 0.1-0.3 eV is usually assumed [1]. To investigate this assumption of LTE, we exposed a W target (Tsurf=300 K) to an argon plasma in PSI-2 and measured the intensity of several W I lines over the first few mm in front of the target with high spatial resolution of 50 µm/px. The position of the intensity maximum provides information about the temporal evolution of the level population. Thus, the assumption on LTE condition within the 5D ground term of the sputtered particles entering the plasma can be studied independently. The data suggest that at a biased, monoenergetic ion energy of 100-200 eV all atoms are sputtered primarily in the lowest ground level 5D0 and the other levels are populated subsequently in the plasma.
[1] I. Beigman et al. Plasma Phys. Control. Fusion 49 1833 (2007)