|approved||turnbull_sherwood16_abstract.pdf||2016-02-13 00:37:45||Alan Turnbull|
Author: Alan D. Turnbull
Requested Type: Poster
Submitted: 2016-02-13 00:35:30
Co-authors: J.M. Hanson, F. Turco, and B.C. Lyons
P.O. Box 85608
San Diego, CA 92186-5
The scaling of the growth rate for resistive external kink magnetohydrodynamic (MHD) instabilities responsible for the ideal-like disruptive instabilities in DIII-D limited and diverted discharges with q95 < 2, and calculated with the MARS code, is shown to follow a fractional power scaling with respect to the plasma resistivity, , but with variable exponents 0 < ν < 1. Resistive MHD instabilities characteristically show fractional power scalings, for example, for the resistive tearing mode where ν = 3/5 and internal resistive kink modes with scaling exponent ν = 1/3 . Even though the resistivity is a small parameter, the resulting growth rates are thus large and competitive with ideal growth rates. The external resistive kink has recently been shown to be responsible for the ideal-like disruptive instabilities in DIII-D limited and diverted discharges with q95 < 2. While the scaling for these modes is found to have a fractional exponent, the exponent is variable. For the limiter discharges with a realistic resistivity profile increasing rapidly in the edge, ν varies continuously from ν = 1 at low η to ν ~ 0 at very high η. For the diverted case, ν varies from ν ~ 1/2 at low η to 1/3 at high η. In contrast to the internal kink studies, there appears to be no transition in mode structure. Additionally, the limiter and divertor scalings are different; the transition in the latter from ν ~ ½ (or from ν ~3/5) to ν ~ 1/3 shows a possible discontinuity.
 Huysmans G.T.A., et al, Phys. Plasmas B5, 1545 1993
This work supported in part by the U.S. Department of Energy (DOE) Fusion Energy Sciences Postdoctoral Research Program along with DOE grant numbers DE-FG02-95ER54309 and DE-FC02-06ER54873l.