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Correlation of Density Pedestal Width and Neutral Penetration Length
Author(s) -
Xu X. Q.,
Nevins W. M.,
Cohen R. H.,
Rognlien T. D.,
Umansky M. V.
Publication year - 2004
Publication title -
contributions to plasma physics
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.531
H-Index - 47
eISSN - 1521-3986
pISSN - 0863-1042
DOI - 10.1002/ctpp.200410015
Subject(s) - pedestal , plasma , physics , turbulence , atomic physics , penetration (warfare) , materials science , mechanics , nuclear physics , archaeology , operations research , engineering , history
Pedestal studies in DIII‐D and MAST find good correlation between the width of the H‐mode density barrier and the neutral penetration length [1, 2]. These results suggest that the width may be set by the combined effects of neutrals and plasma transport. This paper is a report on fluid simulations of boundary plasma using the BOUT code[3] with a neutral source added. Thus both neutral and plasma physics are treated. The plasma transport is self‐consistently driven by boundary turbulence due to the resistive X‐point mode, while neutrals are described by a simple analytic model. The plasma profiles are evolved on the same time scale as the turbulence for the given heat source from the core plasma and particle source from the neutrals. For prescribed neutral profiles, we find the formation of a density pedestal inside the separatrix in the L‐mode even though the calculated plasma diffusion coefficients are almost radially constant and without the formation of a temperature pedestal. These results support the hypothesis that particle fueling can provide the dominant control for the size of the H‐mode density barrier. The width of the density barrier decreases as the pedestal density increases which is also consistent with experimental data. (© 2004 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)