University of Cambridge > Talks.cam > DAMTP Astrophysics Seminar > IMPACT OF MAGNETIC TOPOLOGY ON PLASMA DYNAMICS

IMPACT OF MAGNETIC TOPOLOGY ON PLASMA DYNAMICS

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If you have a question about this talk, please contact Dr. Yufeng Lin.

How is a plasma’s evolution affected by its global magnetic field structure? I will focus on trying to understand the self-organisation of turbulently relaxing plasma – a phenomenon observed in laboratory devices and hypothesised to occur in astrophysical plasmas such as stellar atmospheres. If these plasmas were perfect electrical conductors, their magnetic topology (linkage and connectivity of their magnetic field lines) would be perfectly frozen-in for all time. In reality, the turbulent flows lead to very sharp layers of electric current where even a very small resistivity allows for field-line reconnection. Nevertheless, it is well-known that the total magnetic helicity – an overall measure of the topology – remains a robust invariant. Thus the magnetic energy released during the relaxation may be limited by the conservation of total magnetic helicity. Our work goes further: we focus on the possible relevance of additional topological constraints beyond total magnetic helicity. In a turbulently relaxing plasma, we propose that the leading order behaviour is a re-organisation of field-line helicity, which in general will put additional constraints on the dynamics. If the region of turbulent reconnection is localised, one such constraint may be expressed as conservation of the topological degree of the magnetic field-line mapping.

Joint work with Gunnar Hornig and Alexander Russell (University of Dundee).

This talk is part of the DAMTP Astrophysics Seminar series.

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