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PRODID:UW-Madison-Physics-Events
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UID:UW-Physics-Event-8745
DTSTART:20240429T170000Z
DTEND:20240429T181500Z
DTSTAMP:20260413T223302Z
LAST-MODIFIED:20240424T191253Z
LOCATION:1227 Engineering Hall
SUMMARY:“Metastability of stratified magnetohydrodynamic equilibria 
 and their relaxation”\, Plasma Physics (Physics/ECE/NE 922) Seminar\
 , David Hosking\, Princeton University
DESCRIPTION:Astrophysical\, space and fusion plasmas frequently exhibi
 t explosive releases of energy. Motivated by such events\, I consider 
 in this talk the nonlinear stability of stratified magnetohydrodynamic
  equilibria to interchanges of straight magnetic-flux tubes. I demonst
 rate that\, even under this restricted class of motions\, plasma equil
 ibria can be linearly stable while nonlinearly unstable\, i.e.\, metas
 table. When destabilized\, they can release their stored energy explos
 ively. I show that the available energy with respect to interchanges c
 an be determined accurately by solving a combinatorial optimization pr
 oblem. The states with least energy are\, to good approximation\, the 
 final states reached by simulations of the relaxation of metastable eq
 uilibria\, provided that turbulent mixing is suppressed by viscosity. 
 To predict the result of fully turbulent relaxation\, I construct a st
 atistical mechanical theory based on the maximization of Boltzmann's m
 ixing entropy. This theory is analogous to the Lynden-Bell statistical
  mechanics of stellar systems and collisionless plasmas. The theory re
 produces well the results of numerical simulations for sufficiently la
 rge initial perturbations to the metastable equilibrium.
URL:https://www.physics.wisc.edu/events/?id=8745
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