Impurity transport studies at Wendelstein 7-X by means of x-ray imaging spectrometer measurements

A. Langenberg*, F. Warmer, G. Fuchert, O. Marchuk, A. Dinklage, Th Wegner, J.A. Alonso, S. Bozhenkov, K. J. Brunner, R. Burhenn, B. Buttenschön, P. Drews, B. Geiger, Olaf Grulke, M. Hirsch, U. Höfel, K.P. Hollfeld, C. Killer, J. Knauer, T. KringsF. Kunkel, U. Neuner, G. Offermanns, N.A. Pablant, E. Pasch, K. Rahbarnia, G. Satheeswaran, J. Schilling, B Schweer, H. Thomsen, P. Traverso, R.C. Wolf

*Corresponding author for this work

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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.
Original languageEnglish
Article number014030
JournalPlasma Physics and Controlled Fusion
Volume61
Issue number1
Number of pages8
ISSN0741-3335
DOIs
Publication statusPublished - 2019

Bibliographical note

Original content from this work may be used under the terms of the Creative Commons Attribution 3.0 licence. Any further distribution of this work must maintain attribution to the author(s) and the title of the work, journal citation and DOI.

Keywords

  • Impurity transport
  • Impurity confinement
  • Energy confinement
  • Imaging spectrometer
  • Laser blow-off
  • Plasma physics

Cite this

Langenberg, A., Warmer, F., Fuchert, G., Marchuk, O., Dinklage, A., Wegner, T., 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., ... Wolf, R. C. (2019). Impurity transport studies at Wendelstein 7-X by means of x-ray imaging spectrometer measurements. Plasma Physics and Controlled Fusion, 61(1), [014030]. https://doi.org/10.1088/1361-6587/aaeb74