Stability Properties and Intermittent Failed Eruptions of Arched, Line-Tied Magnetic Flux Ropes

Abstract:

Coronal mass ejections occur when long-lived magnetic flux ropes (MFR) anchored to the solar surface destabilize and erupt away from the Sun. These eruptions are often studied in terms of two ideal magnetohydrodynamic (MHD) instabilities, the kink and torus instabilities. These instabilities have long been considered in axisymmetric fusion devices where their instability criteria are given in terms of the edge safety factor and confining magnetic field decay index, respectively. Laboratory experiments have been performed in the Magnetic Reconnection Experiment (MRX). The ropes were created inside MRX by an arc discharge where current was quasi-statically injected into the ropes during their lifetime which lasted many Alfvén times. This long lifetime allows for the study of MHD properties in the MFRs and the application to solar flux ropes. The equilibrium and stability properties of each MFR were controlled via the external vacuum fields generated by magnetic coils. The external field was analogous to the magnetic arcades in which solar MFRs live and the coils to the subsurface currents in the Sun. A recent observation in these experiments is the existence of ropes which `intermittently’ erupt. These ropes have stable periods, lasting longer than an Alfvén time, interrupted by quick rises which end when the rope falls back down to the stable height before it can fully erupt. This repeated behavior is similar to the storage and release in homologous events on the Sun. The work presented here investigates several potential causes for both the initiation of the eruptive events and the collapse back to stability. Understanding the trigger mechanism for the intermittent ropes also gives insight into the stability criteria for other MFR experiments performed in MRX.