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Title: Drift effects on W7-X divertor heat and particle fluxes

Abstract

Classical particle drifts are known to have substantial impacts on fluxes of particles and heat through the edge plasmas in both tokamaks and stellarators. Here we present results from the first dedicated investigation of drift effects in the W7-X stellarator. By comparing similar plasma discharges conducted with a forward- and reverse-directed magnetic field, the impacts of drifts could be isolated through the observation of up-down asymmetries in flux profiles on the divertor targets. In low-density plasmas, the radial locations of the strike lines (i.e. peaks in the target heat flux profiles) exhibited discrepancies of up to 3 cm that reversed upon magnetic field reversal. In addition, asymmetric heat loads were observed in regions of the target that are shadowed by other targets from parallel flux from the core plasma. A comparison of these asymmetric features with the footprints of key topological regions of the edge magnetic field on the divertor suggests that the main driver of the asymmetries at low density is poloidal E × B drift due to radial electric fields in the scrape-off layer and private flux region. In higher-density plasmas, upper and lower targets collected non-ambipolar currents with opposite signs that also inverted upon field reversal. Overall,more » in these experiments, almost all up-down asymmetry could be attributed to the field reversal and, therefore, field-dependent drifts.« less

Authors:
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Publication Date:
Research Org.:
Los Alamos National Laboratory (LANL), Los Alamos, NM (United States); Princeton Plasma Physics Laboratory (PPPL), Princeton, NJ (United States)
Sponsoring Org.:
USDOE Office of Science (SC). Fusion Energy Sciences (FES); EUROfusion Consortium
Contributing Org.:
the W7-X team; the W7-X Team
OSTI Identifier:
1604031
Alternate Identifier(s):
OSTI ID: 1668681
Report Number(s):
LA-UR-19-23948; 2020-178
Journal ID: ISSN 0741-3335; TRN: US2104182
Grant/Contract Number:  
89233218CNA000001; AC02-09CH11466; 633053
Resource Type:
Accepted Manuscript
Journal Name:
Plasma Physics and Controlled Fusion
Additional Journal Information:
Journal Volume: 61; Journal Issue: 12; Journal ID: ISSN 0741-3335
Publisher:
IOP Science
Country of Publication:
United States
Language:
English
Subject:
70 PLASMA PHYSICS AND FUSION TECHNOLOGY; Magnetic Fusion Energy

Citation Formats

Hammond, K. C., Gao, Y., Jakubowski, M., Killer, C., Niemann, H., Rudischhauser, L., Ali, A., Andreeva, T., Blackwell, B. D., Brunner, K. J., Cannas, B., Drewelow, P., Drews, P., Endler, M., Feng, Y., Geiger, J., Grulke, O., Knauer, J., Klose, S., Lazerson, S., Otte, M., Pisano, F., Neuner, U., Sitjes, A. Puig, Rahbarnia, K., Schilling, J., Thomsen, H., and Wurden, G. A. Drift effects on W7-X divertor heat and particle fluxes. United States: N. p., 2019. Web. doi:10.1088/1361-6587/ab4825.
Hammond, K. C., Gao, Y., Jakubowski, M., Killer, C., Niemann, H., Rudischhauser, L., Ali, A., Andreeva, T., Blackwell, B. D., Brunner, K. J., Cannas, B., Drewelow, P., Drews, P., Endler, M., Feng, Y., Geiger, J., Grulke, O., Knauer, J., Klose, S., Lazerson, S., Otte, M., Pisano, F., Neuner, U., Sitjes, A. Puig, Rahbarnia, K., Schilling, J., Thomsen, H., & Wurden, G. A. Drift effects on W7-X divertor heat and particle fluxes. United States. https://doi.org/10.1088/1361-6587/ab4825
Hammond, K. C., Gao, Y., Jakubowski, M., Killer, C., Niemann, H., Rudischhauser, L., Ali, A., Andreeva, T., Blackwell, B. D., Brunner, K. J., Cannas, B., Drewelow, P., Drews, P., Endler, M., Feng, Y., Geiger, J., Grulke, O., Knauer, J., Klose, S., Lazerson, S., Otte, M., Pisano, F., Neuner, U., Sitjes, A. Puig, Rahbarnia, K., Schilling, J., Thomsen, H., and Wurden, G. A. Wed . "Drift effects on W7-X divertor heat and particle fluxes". United States. https://doi.org/10.1088/1361-6587/ab4825. https://www.osti.gov/servlets/purl/1604031.
@article{osti_1604031,
title = {Drift effects on W7-X divertor heat and particle fluxes},
author = {Hammond, K. C. and Gao, Y. and Jakubowski, M. and Killer, C. and Niemann, H. and Rudischhauser, L. and Ali, A. and Andreeva, T. and Blackwell, B. D. and Brunner, K. J. and Cannas, B. and Drewelow, P. and Drews, P. and Endler, M. and Feng, Y. and Geiger, J. and Grulke, O. and Knauer, J. and Klose, S. and Lazerson, S. and Otte, M. and Pisano, F. and Neuner, U. and Sitjes, A. Puig and Rahbarnia, K. and Schilling, J. and Thomsen, H. and Wurden, G. A.},
abstractNote = {Classical particle drifts are known to have substantial impacts on fluxes of particles and heat through the edge plasmas in both tokamaks and stellarators. Here we present results from the first dedicated investigation of drift effects in the W7-X stellarator. By comparing similar plasma discharges conducted with a forward- and reverse-directed magnetic field, the impacts of drifts could be isolated through the observation of up-down asymmetries in flux profiles on the divertor targets. In low-density plasmas, the radial locations of the strike lines (i.e. peaks in the target heat flux profiles) exhibited discrepancies of up to 3 cm that reversed upon magnetic field reversal. In addition, asymmetric heat loads were observed in regions of the target that are shadowed by other targets from parallel flux from the core plasma. A comparison of these asymmetric features with the footprints of key topological regions of the edge magnetic field on the divertor suggests that the main driver of the asymmetries at low density is poloidal E × B drift due to radial electric fields in the scrape-off layer and private flux region. In higher-density plasmas, upper and lower targets collected non-ambipolar currents with opposite signs that also inverted upon field reversal. Overall, in these experiments, almost all up-down asymmetry could be attributed to the field reversal and, therefore, field-dependent drifts.},
doi = {10.1088/1361-6587/ab4825},
journal = {Plasma Physics and Controlled Fusion},
number = 12,
volume = 61,
place = {United States},
year = {2019},
month = {10}
}

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Cited by: 31 works
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Figures / Tables:

Figure 1 Figure 1: (a) Geometry of the W7-X low-iota magnetic configuration, including the LCFS (red), a flux surface within the edge island (pink) that wraps helically around the LCFS, and the ten divertor targets (dark gray). Translucent planes indicate cross-sections at key toroidal angles referred to in this paper, including themore » location of the multipurpose manipulator (−159°), the lower-divertor (−81°) and upper-divertor (−63°) Langmuir probe arrays, and a cross-section between target modules (36°). (b) Poincaré cross-sections corresponding to each of the translucent planes in (a), including the island separatrix (red), island flux surfaces (pink), and target components (black).« less

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Works referenced in this record:

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Physics of island divertors as highlighted by the example of W7-AS
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Edge plasma measurements on the OP 1.2a divertor plasmas at W7-X using the combined probe
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A multi-purpose manipulator system for W7-X as user facility for plasma edge investigation
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Works referencing / citing this record:

Effect of toroidal plasma currents on the Wendelstein 7-X Scrape-Off Layer
journal, November 2019

  • Killer, Carsten; Gao, Yu; Perseo, Valeria
  • Plasma Physics and Controlled Fusion, Vol. 61, Issue 12
  • DOI: 10.1088/1361-6587/ab4f2d