Three-dimensional magnetohydrodynamical simulation of expanding magnetic flux ropes

Abstract

Three-dimensional, time-dependent numerical simulations of the dynamics of magnetic flux ropes are presented. The simulations are targeted towards an experiment previously conducted at CalTech (Bellan, P. M. and J. F. Hansen, Phys. Plasmas, 5, 1991Plasmas, 5, (1998) which aimed at simulating Solar prominence eruptions in the laboratory. The plasma dynamics is described by ideal MHD using different models for the evolution of the mass density. Key features of the reported experimental observations like pinching of the current loop, its expansion and distortion into helical shape are reproduced in the numerical simulations. Details of the final structure depend on the choice of a specific model for the mass density.

Magnetically Driven Flows in Arched Plasma Structures

“…Computational models that assume reduced dimensionality [7,8], zero velocity at the boundary [9], or periodic boundary conditions [10] may not fully capture boundary interactions. Furthermore, questions have been raised about force-free assumptions [11] in solar coronal models, and about the mechanisms for transporting magnetic flux into the corona [8].…”

Numerical simulation of current sheet formation in a quasiseparatrix layer using adaptive mesh refinement

“…the limit of high wave speeds, we replace the continuity equation by a direct prescription of a relaxation mass density, namely ρ := B 2 . This approach results in an homogeneous Alfvén velocity c A := |B|/ √ ρ = 1 and fast communication of unbalanced forces throughout the system, which shortens relaxation times and has been successfully used in other studies [11].…”

Apex Dips of Experimental Flux Ropes: Helix or Cusp?

“…This feature is a downward dip present at the loop apex as shown in Figure 1(a). Until now, the dip seen in the images has been interpreted as the projection of a helical loop axis generated by the kink instability (Hansen & Bellan 2001;Arnold et al 2008;Stenson & Bellan 2012). However, there are several problems with this interpretation.…”

“…Despite these measurements of density modulation, many models of coronal structures assume constant density (Tokman & Bellan 2002;Arnold et al 2008;Wiegelmann & Sakurai 2012;Jiang et al 2014;Inoue 2016). The experimental results indicate that density perturbations can result in large distortions of an erupting flux rope, even in the absence of significant pressure or gravitational forces.…”

“…Third, kink modes should grow but the dip remains a constant size. Lastly, the dip feature only appears in certain experiments (Hansen & Bellan 2001;Arnold et al 2008;Stenson & Bellan 2012;Ha & Bellan 2016), but not in others with similar physics (Tripathi & Gekelman 2013;Myers et al 2016). An alternative to the helical interpretation is that the dip is a sharp downward cusp, but this interpretation has no obvious formation mechanism and has consequently not been considered until now.…”