Reverse Current Model for Coronal Mass Ejection Cavity Formation

Abstract

We report here a new model for explaining the three-part structure of coronal mass ejections (CMEs). The model proposes that the cavity in a CME forms because a rising electric current in the core prominence induces an oppositely directed electric current in the background plasma; this eddy current is required to satisfy the frozen-in magnetic flux condition in the background plasma. The magnetic force between the inner-core electric current and the oppositely directed induced eddy current propels the background plasma away from the core, creating a cavity and a density pileup at the cavity edge. The cavity radius saturates when an inward restoring force from magnetic and hydrodynamic pressure in the region outside the cavity edge balances the outward magnetic force. The model is supported by (i) laboratory experiments showing the development of a cavity as a result of the repulsion of an induced reverse current by a rising inner-core flux-rope current, (ii) 3D numerical magnetohydrodynamic (MHD) simulations that reproduce the laboratory experiments in quantitative detail, and (iii) an analytic model that describes cavity formation as a result of the plasma containing the induced reverse current being repelled from the inner core. This analytic model has broad applicability because the predicted cavity widths are relatively independent of both the current injection mechanism and the injection timescale.

Magnetic Rayleigh–Taylor Instability in an Experiment Simulating a Solar Loop

“…For a typical solar prominence, a representative value for mass density is´--5 10 kg m 10 3 (Hirayama 1986). The pressure is in the range 0.01-0.1 Pa and a representative value is 0.05 Pa (Hanssen 1995). The magnetic field is about 3-26 G and a representative value is 12 G (Leroy 1988).…”

Magnetically Induced Current Piston for Generating Extreme-ultraviolet Fronts in the Solar Corona

“…Any coaxial current distribution tends to have separation between the forward and reverse currents because anti-parallel currents repel. Consequently, the return current layer will be forced away from the core current, forming a cavity region in between (Haw et al 2018). The expanding reverse current layer effectively serves as a magnetic piston pushing background plasma out in the radial direction ( Figure 2).…”

“…The total expansive force and confining force can be calculated as shown in Haw et al (2018), giving the normalized integrable equation of motion for the magnetic piston to be…”

“…This work is an extension of the cavity model in Haw et al (2018) with an emphasis on the piston-driven shock mechanism. We describe in Section 2 a simple analytic model for an expanding compressional current layer at the surface of a CME and show that this model is consistent with all the observed properties of EUV waves.…”

Determination of a macro- to micro-scale progression leading to a magnetized plasma disruption

“…We have made a 3D ideal MHD numerical simulation of a current-carrying ux rope to model the experimentally observed MHD instability sequence. This simulation, done on the Los Alamos Turquoise cluster, uses part of the Los Alamos COMPutational Astrophysical Simulation Suite (LA-COMPASS) [32,33]. The simulation solves the 3D ideal MHD equa- ux tube evolves with an initial skin current conguration and initial small aspect ratio L/a.…”