Impurity transport studies at Wendelstein 7-X by means of x-ray imaging spectrometer measurements*Invited paper published as part of the Proceedings of the 45th Conference on Plasma Physics (EPS), Prague, Czech Republic, July, 2018. (23rd November 2018)

• Record Type: Journal Article
• Authors: Langenberg, A; Warmer, F; Fuchert, G; Marchuk, O; Dinklage, A; Wegner, Th; Alonso, J A; Bozhenkov, S; Brunner, K J; Burhenn, R; Buttenschön, B; Drews, P; Geiger, B; Grulke, O; Hirsch, M; Höfel, U; Hollfeld, K P; Killer, C; Knauer, J; Krings, T; Kunkel, F; Neuner, U; Offermanns, G; Pablant, N A; Pasch, E; Rahbarnia, K; Satheeswaran, G; Schilling, J; Schweer, B; Thomsen, H; Traverso, P; Wolf, R C;
• Other Names: collab.
• Is Part Of: Plasma physics and controlled fusion. Volume 61:Number 1(2019)
• Publication Date: 2018-11-23
• Subjects: impurity transport -- impurity confinement -- energy confinement -- imaging spectrometer -- laser blow-off -- plasma physics; Plasma (Ionized gases) -- Periodicals; Controlled fusion -- Periodicals; 530.44
• DOI: 10.1088/1361-6587/aaeb74
• Languages: English
• ISSNs: 0741-3335

Abstract

Abstract: This paper reports on the effect of on- and off-axis heating power deposition on the impurity confinement in purely electron cyclotron resonance heated He plasmas on the stellarator Wendelstein 7-X. Therefore, impurity transport times τ I have been determined after Fe impurity injections by laser ablations and monitoring the temporal impurity emissivities by the x-ray imaging spectrometer HR-XIS. A significant increase of τ I has been observed when changing the power deposition from on- to off-axis heating with energy confinement times τ E being mainly unaffected. In addition, the scaling of impurity transport properties with respect to a variation of heating power P ECRH and electron density n e has been investigated by keeping the heating power deposition on-axis. The observed τ I scaling compares well to known τ I scaling laws observed in other machines. A comparison of τ I and τ E yields an averaged ratio of τ E / τ I = 1.3 and transport times in the range of τ I = 40–130 ms and τ E = 40–190 ms. Comparing those absolute values to neoclassical predictions supports the recently observed nature of anomalous transport in Wendelstein 7-X, given within the up to now investigated operational parameters.