Bonn 2020 – scientific programme
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EP: Fachverband Extraterrestrische Physik
EP 2: Sun and Heliosphere I
EP 2.4: Talk
Tuesday, March 31, 2020, 12:00–12:15, H-HS VIII
Parametric Study of Torus Instability Threshold — •Jun Chen1,2, Bernhard Kliem2, Tibor Török3, and Rui Liu1 — 1University of Science and Technology of China — 2University of Potsdam — 3Predictive Science Inc.
A parametric numerical study of the torus instability threshold for the Titov-Démoulin (tokamak) equilibrium of a line-tied, force-free current channel and flux rope is performed to elucidate the scatter about the nominal value of 3/2 for the critical decay index, which characterizes the equilibrium external poloidal field (the so-called strapping field). Values scattering in the range ≈ 1–2 are typically found in numerical and observational studies of flux rope eruptions on the Sun. We demonstrate and quantify the stabilizing effects of an external toroidal (shear, or guide) field component and of pure O-type topology, which forms when the bounding separatrix surface of the flux rope fully touches the photospheric boundary, delaying the onset of fast magnetic reconnection relative to the onset of instability. Increasing flux rope thickness, considered for decreasing aspect ratios down to ≈ 2, is also found to raise the threshold.