Investigation of TESPEL cloud dynamics in Wendelstein 7-X stellarator

Abstract Tracer-encapsulated solid pellet (TESPEL) was injected from the outboard midplane into Wendelstein 7-X (W7-X) plasmas. Viewing from behind the flight path, the distribution of the light emissions from the TESPEL cloud particles (H, C and C 2+ ) was recorded using an ultrafast visible camera...

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Bibliographic Details
Published in:Nuclear fusion 2021-01, Vol.61 (1), p.16006
Main Authors: Kocsis, G., Tamura, N., Bussiahn, R., McCarthy, K.J., Baldzuhn, J., Biedermann, C., Cseh, G., Damm, H., Kornejew, P., König, R., Panadero, N., Szepesi, T.
Format: Article
Language:English
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Summary:Abstract Tracer-encapsulated solid pellet (TESPEL) was injected from the outboard midplane into Wendelstein 7-X (W7-X) plasmas. Viewing from behind the flight path, the distribution of the light emissions from the TESPEL cloud particles (H, C and C 2+ ) was recorded using an ultrafast visible camera with a temporal resolution up to 2 µ s, which allows resolving both the pellet cloud evolution and the detachment of the drifting cloud. It was observed that both the B┴ and the B║ aligned dimensions of the pellet cloud fluctuate quasi-periodically, this being associated with a vertical cloud movement and an eruption/ejection of part of the cloud. It is found that, first, the pellet cloud expands parallel to the magnetic field lines for about 10 µ s. Then, when the cloud reaches a certain B║ size the ionized part of the cloud (plasmoid) moves vertically (typically upwards) and detaches itself from the pellet within 10 µ s. One possible explanation for the upward movement of the pellet cloud is the presence of a vertical component of grad(B) pointing downward resulting in an upward cloud drift.
ISSN:0029-5515
1741-4326
DOI:10.1088/1741-4326/abbc84