Laboratory Identification of MHD Eruption Criteria in the Solar Corona

Abstract:

Ideal magnetohydrodynamic (MHD) instabilities such as the kink [1] and torus [2] instabilities are believed to play an important role in driving “storage-and-release” eruptions in the solar corona. These instabilities act on long-lived, arched magnetic flux ropes that are “line-tied” to the solar surface. In spite of numerous observational and computational studies, the conditions under which these instabilities produce an eruption remain a subject of intense debate. In this paper, we use a line-tied, arched flux rope experiment to study storage-and-release eruptions in the laboratory [3]. An in situ array of miniature magnetic probes is used to assess the equilibrium and stability of the laboratory flux ropes. Two major results are reported here: First, a new stability regime is identified where torus-unstable flux ropes fail to erupt. In this “failed torus” regime, the flux rope is torus-unstable but kink-stable. Under these conditions, a dynamic “toroidal field tension force” surges in magnitude and causes the flux rope to contract. This tension force, which is missing from existing eruption models, is the J×B force between self-generated poloidal currents in the flux rope and the toroidal (guide) component of the vacuum field. Secondly, a clear torus instability threshold is observed in the kink-unstable regime. This latter result, which is consistent with existing theoretical [4] and numerical [5] findings, verifies the key role of the torus instability in driving some solar eruptions.

This research is supported by DoE Contract No. DE-AC02-09CH11466 and by the NSF/DoE Center for Magnetic Self-Organization (CMSO).

[1] Hood & Priest, Geophys. Astrophys. Fluid Dynamics 17, 297 (1981)

[2] Kliem & Török, Phys. Rev. Lett. 96, 255002 (2006)

[3] Myers, Ph.D. Thesis, Princeton University (2015)

[4] Olmedo & Zhang, Astrophys. J. 718, 433 (2010)

[5] Török & Kliem, Astrophys. J. 630, L97 (2005)