Tearing mode formation and radiative edge cooling prior to density limit disruptions in ASDEX upgrade
- 1 January 1997
- journal article
- Published by IOP Publishing in Nuclear Fusion
- Vol. 37 (1) , 119-125
- https://doi.org/10.1088/0029-5515/37/1/i09
Abstract
Tearing mode formation is investigated for ohmic density limit discharges on the ASDEX Upgrade tokamak at medium and high safety factors (q95=3.8, 4.9, 6.0). Low electron temperatures inside magnetic islands and the observation of localized C III impurity radiation suggest that a thermal instability, as proposed by Rebut and Hugon, destabilizes the (m, n)=(3,1) and (4,1) islands, which grow during the current profile contraction phase. In contrast, the (2,1) islands appear to be thermally stable. Minor disruptions lead to step-wise loss of confinement, first localized at the 4 2 surface, then after a time delay comparable to the resistive time-scale, at the q=3 surface and after a second time delay, at the q=4 surface. It is found that (3,1) islands, unlike (2,1) islands, are quenched by the high heat flux during minor disruptionsKeywords
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