H-mode physics of near double null plasmas in MAST and its applications to other tokamaks

H. Meyer, P. G. Carolan, G. D. Conway, G. Cunningham, L. D. Horton, A. Kirk, R. Maingi, F. Ryter, S. Saarelma, J. Schirmer, W. Suttrop, H. R. Wilson

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42 Scopus citations

Abstract

High triangularity regimes, approaching double null, have become more important recently. H-mode access and edge stability are affected by the close proximity of the second X-point to the last closed flux surface, but more experimental evidence is needed. Inter-machine comparisons of MAST with ASDEX Upgrade (AUG) and NSTX confirm the reduction of the H-mode power threshold in the true double null configuration (C-DN), first reported on MAST. A more negative radial edge electric field in L-mode observed on MAST and ASDEX Upgrade may be connected to the improved H-mode access. About twice the power density is needed on MAST to achieve edge pressures similar to AUG in L- and H-modes. However, on MAST the pressure is dominated by the edge density in H-mode. So far, in single null (SN) ELMs have not been observed on MAST with neutral beam heating powers PNBI ≤ 2 MW, due to the different edge profiles in SN H-mode. This is supported by the modelling of the stability of the measured edge profiles against ideal peeling-ballooning.

Original languageEnglish
Pages (from-to)64-72
Number of pages9
JournalNuclear Fusion
Volume46
Issue number1
DOIs
StatePublished - Jan 1 2006
Externally publishedYes

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