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SUMMARY:IMPACT OF MAGNETIC TOPOLOGY ON PLASMA DYNAMICS - Anthony Yeates (D
 urham University)
DTSTART:20180226T140000Z
DTEND:20180226T150000Z
UID:TALK96973@talks.cam.ac.uk
CONTACT:Dr. Yufeng Lin
DESCRIPTION:How is a plasma's evolution affected by its global magnetic fi
 eld\nstructure? I will focus on trying to understand the self-organisation
  of\nturbulently relaxing plasma - a phenomenon observed in laboratory\nde
 vices and hypothesised to occur in astrophysical plasmas such as\nstellar 
 atmospheres. If these plasmas were perfect electrical\nconductors\, their 
 magnetic topology (linkage and connectivity of their\nmagnetic field lines
 ) would be perfectly frozen-in for all time. In\nreality\, the turbulent f
 lows lead to very sharp layers of electric\ncurrent where even a very smal
 l resistivity allows for field-line\nreconnection. Nevertheless\, it is we
 ll-known that the total magnetic\nhelicity - an overall measure of the top
 ology - remains a robust\ninvariant. Thus the magnetic energy released dur
 ing the relaxation may\nbe limited by the conservation of total magnetic h
 elicity. Our work goes\nfurther: we focus on the possible relevance of add
 itional topological\nconstraints beyond total magnetic helicity. In a turb
 ulently relaxing\nplasma\, we propose that the leading order behaviour is 
 a re-organisation\nof field-line helicity\, which in general will put addi
 tional constraints\non the dynamics. If the region of turbulent reconnecti
 on is localised\,\none such constraint may be expressed as conservation of
  the topological\ndegree of the magnetic field-line mapping.\n\nJoint work
  with Gunnar Hornig and Alexander Russell (University of Dundee).
LOCATION:MR14\,  Centre for Mathematical Sciences\, Wilberforce Road\, Cam
 bridge
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