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  Transport in island divertors: physics, 3D modelling and comparison to first experiments on W7-AS

Feng, Y., Sardei, F., Grigull, P., McCormick, K., Kisslinger, J., Reiter, D., et al. (2002). Transport in island divertors: physics, 3D modelling and comparison to first experiments on W7-AS. Plasma Physics and Controlled Fusion, 44(5), 611-625.

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 Creators:
Feng, Y.1, 2, Author              
Sardei, F.1, Author              
Grigull, P.3, Author              
McCormick, K.4, Author              
Kisslinger, J.1, 2, Author              
Reiter, D.5, Author
Igitkhanov, Y.1, 2, 6, Author              
Affiliations:
1Experimental Plasma Physics 3 (E3), Max Planck Institute for Plasma Physics, Max Planck Society, ou_1856291              
2W7-AS, Max Planck Institute for Plasma Physics, Max Planck Society, ou_1856310              
3W7-X: Physics (PH), Max Planck Institute for Plasma Physics, Max Planck Society, ou_1856305              
4Stellarator Scenario Development (E5), Max Planck Institute for Plasma Physics, Max Planck Society, ou_1856285              
5KFA Julich GmbH, Forschungszentrum, EURATOM Assoc, Inst Plasma Phys, D-52425 Julich, Germany, ou_persistent22              
6Stellarator System Studies, Max Planck Institute for Plasma Physics, Max Planck Society, ou_1856331              

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 Abstract: Basic plasma transport properties in island divertors are compared to those of standard tokamak divertors. A realistic plasma transport modelling of high-density discharges in island divertors has become possible by implementing a self-consistent treatment of impurity transport in the EMC3-EIRENE code. In contrast to standard tokamak divertors, the code predicts no high recycling prior to detachment, with the downstream density never exceeding the upstream density. This is mainly due to momentum losses arising from the cross-field transport associated with the specific island divertor geometry. This momentum loss is effective already at low densities, high temperatures and is responsible for the high upstream densities needed to achieve detachment. Numerical scans of carbon concentration for high-density plasma typically show first a smooth, then a sharp increase of the carbon radiation, the latter being accompanied by a sharp drop of the downstream temperature and density indicating detachment transition. The jumps of the radiation and temperature are due to a thermal instability associated with the form of the impurity cooling rate function and can be reproduced by a simple ID radial energy model based on cross-field transport and impurity losses. This model is used as a guideline to illustrate and discuss the detachment physics in details, including detachment condition and thermal instability. Major EMC3-EIRENE code predictions have been verified by the first W7-AS divertor experiments. A comparison of calculations and measurements is presented for high-density, high-power W7-AS divertor discharges and the physics related to rollover and detachment is discussed in detail. The code has been recently extended to general SOL configurations with open islands and arbitrary ergodicity by using a new highly accurate field-line mapping technique. The method correctly reproduces flux surfaces and islands over a high number of toroidal field periods, thus ensuring a clear distinction between parallel and radial transport. The technique has been tested successfully on W7-AS, W7-X, LHD and TEXTOR DED, and first applied to solve the coupled heat conduction equations for a typical ergodic W7-AS configuration.

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Language(s): eng - English
 Dates: 2002-05
 Publication Status: Published in print
 Pages: -
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 Table of Contents: -
 Rev. Type: Peer
 Identifiers: eDoc: 20455
ISI: 000180774600009
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Title: Plasma Physics and Controlled Fusion
  Alternative Title : Plasma Phys. Control. Fusion
Source Genre: Journal
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Pages: - Volume / Issue: 44 (5) Sequence Number: - Start / End Page: 611 - 625 Identifier: ISSN: 0741-3335