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P: Fachverband Plasmaphysik
P 4: Magnetic Confinement II
P 4.3: Talk
Tuesday, August 31, 2021, 11:45–12:00, H5
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 Energeticas, Medioambientales y Tecnologicas
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. The deposited tracers are localized within the plasma from time-of-flight measurements. The temporal dynamics of the shell ablation is well reproduced by neutral gas shielding models. This confirms the applicability of the tracer localisation method. The spectral line emission time-traces of various tracer ion charge states show 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. First impurity transport studies by means of the code STRAHL resulted in a good reproduction of the line emission time-traces and confirm the important role of anomalous transport in W7-X, as reported for LBO injections before.