Title: Effect of 3D magnetic perturbations on divertor conditions and detachment in tokamak and stellarator

Abstract

Enhanced perpendicular heat and momentum transport induces parallel pressure loss leading to divertor detachment, which can be produced by the increase of density in 2D tokamaks. However, in the 3D configurations such as tokamaks with 3D fields and stellarators, the fraction of perpendicular transport can be higher even in a lower density regime, which could lead to the early transition to detachment without passing through the high-recycling regime. 3D fields applied to the limiter tokamak plasmas produce edge stochastic layers close to the last closed flux surface (LCFS), which can allow for enhanced perpendicular transport and indeed the absence of high recycling regime and early detachment have been observed in TEXTOR and Tore Supra. However, in the X-point divertor tokamaks with the applied 3D fields, the parallel transport is still dominant and the detachment facilitation has not been observed yet. Rather, 3D fields affected detachment adversely under certain conditions, either by preventing detachment onset as seen in DIII-D or by re-attaching the existing detached plasma as shown in NSTX. The possible way for strong 3D effects to induce access to the early detachment in divertor tokamaks appears to be via significant perpendicular loss of parallel momentum by frictional force formore » the counter-streaming flows between neighboring flow channels in the divertor. In principle, the adjacent lobes in the 3D divertor tokamak may generate the counter-streaming flow channels. However, an EMC3-EIRENE simulation for ITER H-mode plasmas demonstrated that screened RMP leads to significantly reduced counter-flows near the divertor target, therefore the momentum loss effect leading to detachment facilitation is expected to be small. This is consistent with the observation in LHD, which showed screening (amplification) of RMP fields in the attachment (stable detachment) case. In conclusion, work for optimal parameter window for best divertor operation scenario is needed particularly for the 3D divertor tokamak configuration.« less

Authors:

Ahn, J. -W. ^[1]; Briesemester, A. R.  ^[1];

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Kobayashi, M. ^[2]; Lore, J. D. ^[1]; Schmitz, O. ^[3]; Diallo, A. ^[4]; Gray, T. K. ^[1]; Lasnier, C. J. ^[5]; LeBlanc, B. P. ^[4]; Maingi, R. ^[4]; McLean, A. G. ^[5]; Sabbagh, S. A. ^[6]; Soukhanovskii, V. A. ^[5]

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+ Show Author Affiliations

1. Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States)
2. National Institute for Fusion Science, Toki (Japan)
3. Univ. of Wisconsin - Madison, Madison, WI (United States)
4. Princeton Plasma Physics Lab. (PPPL), Princeton, NJ (United States)
5. Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States)
6. Columbia Univ., New York, NY (United States)

Publication Date:

Thu Jun 22 00:00:00 EDT 2017

Research Org.:

Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States)

Sponsoring Org.:

USDOE

OSTI Identifier:

1410785

Report Number(s):

LLNL-JRNL-742142
Journal ID: ISSN 0741-3335

Grant/Contract Number:  

AC52-07NA27344

Resource Type:

Accepted Manuscript

Journal Name:

Plasma Physics and Controlled Fusion

Additional Journal Information:

Journal Volume: 59; Journal Issue: 8; Journal ID: ISSN 0741-3335

Publisher:

IOP Science

Country of Publication:

United States

Language:

English

Subject:

70 PLASMA PHYSICS AND FUSION; detachment; 3D fields; RMP; plasma response; diverter plasma regime; 3D effects on divertor