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

Abstract

This study 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 EI = 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.

Authors:
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  1. Max-Planck-Institut fur Plasmaphysik, Greifswald (Germany)
  2. Forschungszentrum Julich GmbH, Julich (Germany)
  3. Lab. Nacional de Fusion, Madrid (Spain)
  4. Max-Planck-Institut fur Plasmaphysik, Greifswald (Germany); Technical Univ. of Denmark DTU, Lyngby (Denmark)
  5. Princeton Plasma Physics Lab. (PPPL), Princeton, NJ (United States)
  6. Auburn Univ., Auburn, AL (United States)
Publication Date:
Research Org.:
Princeton Plasma Physics Lab. (PPPL), Princeton, NJ (United States)
Sponsoring Org.:
USDOE
Contributing Org.:
the W7-X Team
OSTI Identifier:
1485104
Grant/Contract Number:  
No 633053
Resource Type:
Journal Article: Accepted Manuscript
Journal Name:
Plasma Physics and Controlled Fusion
Additional Journal Information:
Journal Volume: 61; Journal Issue: 1; Journal ID: ISSN 0741-3335
Publisher:
IOP Science
Country of Publication:
United States
Language:
English
Subject:
70 PLASMA PHYSICS AND FUSION TECHNOLOGY; impurity transport; impurity confinement; energy confinement; imaging spectrometer; laser blow-off; plasma physics

Citation Formats

Langenberg, Andreas, 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., and Wolf, R. C.. Impurity transport studies at Wendelstein 7-X by means of x-ray imaging spectrometer measurements. United States: N. p., 2018. Web. doi:10.1088/1361-6587/aaeb74.
Langenberg, Andreas, 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.. Impurity transport studies at Wendelstein 7-X by means of x-ray imaging spectrometer measurements. United States. doi:10.1088/1361-6587/aaeb74.
Langenberg, Andreas, 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., and Wolf, R. C.. Fri . "Impurity transport studies at Wendelstein 7-X by means of x-ray imaging spectrometer measurements". United States. doi:10.1088/1361-6587/aaeb74. https://www.osti.gov/servlets/purl/1485104.
@article{osti_1485104,
title = {Impurity transport studies at Wendelstein 7-X by means of x-ray imaging spectrometer measurements},
author = {Langenberg, Andreas and Warmer, F. and Fuchert, G. and Marchuk, O. and Dinklage, A. and Wegner, Th and Alonso, J. A. and Bozhenkov, S. and Brunner, K. J. and Burhenn, R. and Buttenschön, B. and Drews, P. and Geiger, B. and Grulke, O. and Hirsch, M. and Höfel, U. and Hollfeld, K. P. and Killer, C. and Knauer, J. and Krings, T. and Kunkel, F. and Neuner, U. and Offermanns, G. and Pablant, N. A. and Pasch, E. and Rahbarnia, K. and Satheeswaran, G. and Schilling, J. and Schweer, B. and Thomsen, H. and Traverso, P. and Wolf, R. C.},
abstractNote = {This study 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.},
doi = {10.1088/1361-6587/aaeb74},
journal = {Plasma Physics and Controlled Fusion},
issn = {0741-3335},
number = 1,
volume = 61,
place = {United States},
year = {2018},
month = {11}
}

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