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Abstract
Predicting the final state of turbulent plasma relaxation is an important challenge, both in astrophysical plasmas such as the Sun's corona and in controlled thermonuclear fusion. Recent numerical simulations of plasma relaxation with braided magnetic fields identified the possibility of a novel constraint, arising from the topological degree of the magnetic fieldline mapping. This constraint implies that the final relaxed state is drastically different for an initial configuration with topological degree 1 (which allows a Taylor relaxation) and one with degree 2 (which does not reach a Taylor state). Here, we test this transition in numerical resistivemagnetohydrodynamic simulations, by embedding a braided magnetic field in a linear forcefree background. Varying the background forcefree field parameter generates a sequence of initial conditions with a transition between topological degree 1 and 2. For degree 1, the relaxation produces a single twisted flux tube, whereas for degree 2 we obtain two flux tubes. For predicting the exact point of transition, it is not the topological degree of the whole domain that is relevant, but only that of the turbulent region.
Original language  English 

Article number  20150012 
Number of pages  12 
Journal  Proceedings of the Royal Society A: Mathematical, Physical and Engineering Sciences 
Volume  471 
Issue number  2178 
Early online date  8 Jun 2015 
DOIs  
Publication status  Published  8 Jun 2015 
Keywords
 Coronal heating
 Magnetic topology
 Magnetohydrodynamics
 Plasma relaxation
ASJC Scopus subject areas
 Mathematics(all)
 Engineering(all)
 Physics and Astronomy(all)
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 1 Finished

Complex Magnetic Fields: An Enigma of Solar Plasmas (joint with Durham University)
Hornig, G., Pontin, D. & WilmotSmith, A.
Science and Technology Facilities Council
1/04/13 → 30/06/16
Project: Research