Characteristics of the SOL turbulence structure in the first experimental campaign on W7-X with limiter configuration

In the first experimental campaign of Wendelstein 7-X (W7-X), a combined probe head mounted on the multi-purpose manipulator has been used to measure the scrape-off layer (SOL) turbulence characteristics. The preliminary experimental results are summarized to illustrate the SOL turbulence properties...

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Veröffentlicht in:Physics of plasmas 2018-07, Vol.25 (7)
Hauptverfasser: Liu, S. C., Liang, Y., Drews, P., Krämer-Flecken, A., Han, X., Nicolai, D., Satheeswaran, G., Wang, N. C., Cai, J. Q., Charl, A., Cosfeld, J., Gao, Y., Grulke, O., Henkel, M., Hollfeld, K. P., Killer, C., Knieps, A., König, R., Neubauer, O., Rack, M., Sandri, N., Sereda, S., Schweer, B., Wang, E. H., Wei, Y. L.
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Sprache:eng
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Zusammenfassung:In the first experimental campaign of Wendelstein 7-X (W7-X), a combined probe head mounted on the multi-purpose manipulator has been used to measure the scrape-off layer (SOL) turbulence characteristics. The preliminary experimental results are summarized to illustrate the SOL turbulence properties in the limiter configuration on W7-X. In a standard limiter configuration, significant electrostatic fluctuations can be found in the near SOL, and the dominant frequency of fluctuation power is below 100 kHz. The auto-correlation spectrum power law decay factor is α ≈ −1 below 40 kHz and α ≈ –2 between 50 and 200 kHz. A broadband spectrum appears between 240 and 380 kHz with a low spectral power density, but a high cross-correlation coefficient. The statistical characteristics of turbulence are calculated by the two-point cross-correlation technique. A clear poloidal dispersion relation is found in the spectrum S(kθ, f), propagating along the ion diamagnetic drift direction with a group velocity (below 100 kHz) about 0.56 km/s in the near SOL in the laboratory frame. The poloidal correlation length is around 5–10 mm in SOL. The turbulence phase velocity is about 0.5–1 km/s when close to the last closed flux surface, which is comparable with the poloidal E × B drift speed.
ISSN:1070-664X
1089-7674
DOI:10.1063/1.5033353