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Magnetic flux ropes - twisted bundles of magnetic field lines - are ubiquitous and fundamental structures in astrophysical and laboratory plasmas. Importantly, they are reservoirs of free magnetic energy, which may be released in solar flares and in smaller flare-events associated with the heating of the solar corona. Magnetic reconnection allows restructuring of the magnetic field and efficient dissipation of magnetic energy, heating the plasma and generating non-thermal populations of electrons and ions. Reconnection also plays an important role in magnetically-confined fusion plasmas. The ideal kink instability in a twisted flux rope leads to the formation of current sheets and thus triggers magnetic reconnection, in which the field relaxes to a lower energy state. First, I will show how instability in a single magnetic flux rope can lead to a confined solar flare. Using a combination of 3D magnetohydrodynamic (MHD) simulations and test-particles, we predict observable signatures in both thermal and non-thermal emission, and thus propose a means for detection of twisted magnetic fields in the solar corona. Then I will discuss interactions between multiple flux ropes, showing how one unstable flux rope within an array of stable neighbours may trigger a heating avalanche. This has important implications for solar coronal heating. I will also describe MHD and two-fluid simulations of the merging of twisted magnetic tori during merging-compression formation of a spherical tokamak, with application to the MAST device. Some ongoing studies of reconnection of magnetic filaments associated with Edge Localised Modes in tokamaks will also be mentioned. |
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