Hannover 2020 – scientific programme
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P: Fachverband Plasmaphysik
P 15: Helmholtz Graduate School 3 and Magnetic confinement 3
P 15.4: Talk
Wednesday, March 11, 2020, 15:20–15:35, b305
Impurity transport studies on Wendelstein 7-X by Tracer-Encapsulated Solid Pellets (TESPEL) — •René Bussiahn1, Naoki Tamura2, Kieran McCarthy3, and The W7-X team1 — 1Max-Planck-Institute for Plasma Physics, Greifswald, Germany — 2National Institute for Fusion Science(NIFS), Toki, Japan — 3Centro de Investigaciones Energéticas, Medioambientales y Tecnológicas
During OP1.2b operation phase of the stellarator Wendelstein 7-X, the TESPEL injections have proven successfully as a complementary tool to Laser-Blow-Off (LBO) for impurity transport studies. Contrary to LBO - depositing tracers close to the plasma edge which are subsequently transported and spread out into the plasma, TESPEL can release the embedded impurity tracers instantly after the ablation of the protecting polystyrene shell in the core of the plasma within a well defined spatial region of a few cm3. Comparing the temporal dynamics of the shell ablation with a neutral gas shielding model gives good agreement. As seen from fast frame camera images of the shell ablation cloud, the TESPEL trajectory through the plasma does not suffer any deflections. This permits localizing the deposited tracer in the plasma by a simple time-of-flight attempt. The temporal evolution of the line emissions by tracer impurity ions of various charge states, observed by vacuum ultraviolet spectroscopy (HEXOS) and high resolution X-ray imaging spectrometry (HR-XIS) shows distinct differences between LBO and TESPEL, especially in their initial phase. Later, the curves are similar and the related impurity decay times are inversely proportional to the heating power.