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High-confinement NBI discharges in the W7-AS stellarator

Abstract

In W7-AS, the longest energy confinement times were achieved in neutral beam injection heated (NBI-heated) discharges under low wall-recycling conditions. Low recycling is needed to control the density at line-averaged values of n-bar{sub e} approx. 10{sup 20}m{sup -3}. Under these conditions, confinement was improved by a factor of two above the common scaling estimate. The reduction of radial transport is concentrated into a layer at about two-thirds of the plasma radius. In this region steep pressure gradients and a strong gradient in the radial electric field develop. Specific for the discharges is the slow transition to improved confinement, lasting up to three energy confinement times. Since the measured electric field is consistent with the neoclassical ambipolar field, this high-confinement mode could be an example where sheared plasma flow as created by the neoclassical radial electric field leads to a suppression of anomalous transport. (author)
Authors:
Stroth, U; Baldzuhn, J; Geiger, J; Geist, T; Giannone, L.; Hartfuss, H -J; Hirsch, M; Jaenicke, R; Kick, M; Koponen, J P; Kuehner, G; Penningsfeld, F -P; Wagner, F [1] 
  1. Max-Planck-Institut fuer Plasmaphysik, EURATOM Association, D-85748 Garching (Germany)
Publication Date:
Aug 01, 1998
Product Type:
Journal Article
Reference Number:
EDB-00:049824
Resource Relation:
Journal Name: Plasma Physics and Controlled Fusion (Online); Journal Volume: 40; Journal Issue: 8; Other Information: PBD: Aug 1998
Subject:
70 PLASMA PHYSICS AND FUSION TECHNOLOGY; BEAM INJECTION HEATING; NEUTRAL ATOM BEAM INJECTION; PLASMA CONFINEMENT; SCALING LAWS; WALL EFFECTS; WENDELSTEIN-7 STELLARATOR
OSTI ID:
20059616
Country of Origin:
IAEA
Language:
English
Other Identifying Numbers:
Journal ID: ISSN 1361-6587; TRN: XA00J1080022202
Submitting Site:
INIS
Size:
page(s) 1551-1565
Announcement Date:

Citation Formats

Stroth, U, Baldzuhn, J, Geiger, J, Geist, T, Giannone, L., Hartfuss, H -J, Hirsch, M, Jaenicke, R, Kick, M, Koponen, J P, Kuehner, G, Penningsfeld, F -P, and Wagner, F. High-confinement NBI discharges in the W7-AS stellarator. IAEA: N. p., 1998. Web. doi:10.1088/0741-3335/40/8/008.
Stroth, U, Baldzuhn, J, Geiger, J, Geist, T, Giannone, L., Hartfuss, H -J, Hirsch, M, Jaenicke, R, Kick, M, Koponen, J P, Kuehner, G, Penningsfeld, F -P, & Wagner, F. High-confinement NBI discharges in the W7-AS stellarator. IAEA. doi:10.1088/0741-3335/40/8/008.
Stroth, U, Baldzuhn, J, Geiger, J, Geist, T, Giannone, L., Hartfuss, H -J, Hirsch, M, Jaenicke, R, Kick, M, Koponen, J P, Kuehner, G, Penningsfeld, F -P, and Wagner, F. 1998. "High-confinement NBI discharges in the W7-AS stellarator." IAEA. doi:10.1088/0741-3335/40/8/008. https://www.osti.gov/servlets/purl/10.1088/0741-3335/40/8/008.
@misc{etde_20059616,
title = {High-confinement NBI discharges in the W7-AS stellarator}
author = {Stroth, U, Baldzuhn, J, Geiger, J, Geist, T, Giannone, L., Hartfuss, H -J, Hirsch, M, Jaenicke, R, Kick, M, Koponen, J P, Kuehner, G, Penningsfeld, F -P, and Wagner, F}
abstractNote = {In W7-AS, the longest energy confinement times were achieved in neutral beam injection heated (NBI-heated) discharges under low wall-recycling conditions. Low recycling is needed to control the density at line-averaged values of n-bar{sub e} approx. 10{sup 20}m{sup -3}. Under these conditions, confinement was improved by a factor of two above the common scaling estimate. The reduction of radial transport is concentrated into a layer at about two-thirds of the plasma radius. In this region steep pressure gradients and a strong gradient in the radial electric field develop. Specific for the discharges is the slow transition to improved confinement, lasting up to three energy confinement times. Since the measured electric field is consistent with the neoclassical ambipolar field, this high-confinement mode could be an example where sheared plasma flow as created by the neoclassical radial electric field leads to a suppression of anomalous transport. (author)}
doi = {10.1088/0741-3335/40/8/008}
journal = {Plasma Physics and Controlled Fusion (Online)}
issue = {8}
volume = {40}
journal type = {AC}
place = {IAEA}
year = {1998}
month = {Aug}
}