Coronal heating by the partial relaxation of twisted loops

Abstract

Context: Relaxation theory offers a straightforward method for estimating the energy that is released when a magnetic field becomes unstable, as a result of continual convective driving. Aims: We present new results obtained from nonlinear magnetohydrodynamic (MHD) simulations of idealised coronal loops. The purpose of this work is to determine whether or not the simulation results agree with Taylor relaxation, which will require a modified version of relaxation theory applicable to unbounded field configurations. Methods: A three-dimensional (3D) MHD Lagrangian-remap code is used to simulate the evolution of a line-tied cylindrical coronal loop model. This model comprises three concentric layers surrounded by a potential envelope; hence, being twisted locally, each loop configuration is distinguished by a piecewise-constant current profile. Initially, all configurations carry zero-net-current fields and are in ideally unstable equilibrium. The simulation results are compared with the predictions of helicity conserving relaxation theory. Results: For all simulations, the change in helicity is no more than 2% of the initial value; also, the numerical helicities match the analytically-determined values. Magnetic energy dissipation predominantly occurs via shock heating associated with magnetic reconnection in distributed current sheets. The energy release and final field profiles produced by the numerical simulations are in agreement with the predictions given by a new model of partial relaxation theory: the relaxed field is close to a linear force free state; however, the extent of the relaxation region is limited, while the loop undergoes some radial expansion. Conclusions: The results presented here support the use of partial relaxation theory, specifically, when calculating the heating-event distributions produced by ensembles of kink-unstable loops.

References in corpus (2)

• Topological Constraints on Magnetic Relaxation
• The Flare-energy Distributions Generated by Kink-unstable Ensembles of Zero-net-current Coronal Loops

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• Evolution, structure and topology of self-generated turbulent reconnection layers
• Plasma motions and non-thermal line broadening in flaring twisted coronal loops
• Flare particle acceleration in the interaction of twisted coronal flux ropes
• Energy release in driven twisted coronal loops
• The effects of driving time scales on coronal heating in a stratified atmosphere
• Is Magnetic Topology Important for Heating the Solar Atmosphere?
• Spontaneous reconnection at a separator current layer. I. Nature of the reconnection
• Can Multi-Threaded Flux Tubes in Coronal Arcades Support a Magnetohydrodynamic Avalanche?
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