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Increasing the density in Wendelstein 7-X: benefits and limitations

W7-X Team; Fuchert, G.; Brunner, K.J.; Rahbarnia, K.; Stange, T.; Zhang, D.; Baldzuhn, J.; Bozhenkov, S.A.; Beidler, C.D.; Beurskens, M.N.A.; Brezinsek, S.; Burhenn, R.; Damm, H.; Dinklage, A.; Feng, Y.; Hacker, P.; Hirsch, M.; Kazakov, Y.; Knauer, J.; Langenberg, A.; Laqua, H.P.; ... mehr

Abstract (englisch):
In stellarators, increasing the density is beneficial for the energy confinement. While there is no single reason for this observation, it is still very robust across different devices and this is reflected in the empirical energy confinement time scaling for stellarators, ISS04. In order to study whether this is also true for Wendelstein 7-X, the density scaling of the energy confinement time is analyzed and compared to ISS04 for the first divertor experiments. When the density is increased beyond a critical density, however, radiative collapses are frequently observed. Existing analytical models for the critical density are revisited to assess whether they can predict the accessible density range. Furthermore, since close to the collapse the radiation losses increase substantially, the impact on the global energy confinement is investigated. It is found that in plasmas with high radiation the density scaling of the energy confinement time becomes weaker, the reason for this observation is not yet clear. In the second half of the first divertor campaign, boronization was applied to W7-X for the first time. This broadened the operational window, allowing for operation at higher density and, hence, higher stored energy.



Zugehörige Institution(en) am KIT Institut für Hochleistungsimpuls- und Mikrowellentechnik (IHM)
Publikationstyp Zeitschriftenaufsatz
Publikationsmonat/-jahr 03.2020
Sprache Englisch
Identifikator ISSN: 0029-5515, 1741-4326
KITopen-ID: 1000106021
HGF-Programm 31.03.02 (POF III, LK 01)
Plasma Heizsysteme
Erschienen in Nuclear fusion
Band 60
Heft 3
Seiten 036020
Projektinformation EUROfusion (EU, H2020, 633053)
Vorab online veröffentlicht am 19.02.2020
Nachgewiesen in Scopus
Web of Science
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