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SUMMARY:Dynamical and Thermal Stability of the Intracluster Medium: Buoyan
 cy Instabilities and Nanoastrophysics - Matthew Kunz (Oxford)
DTSTART:20110606T150000Z
DTEND:20110606T160000Z
UID:TALK31171@talks.cam.ac.uk
CONTACT:Henrik Latter
DESCRIPTION:In weakly-collisional plasmas such as the intracluster medium 
 (ICM)\, heat and\nmomentum transport become anisotropic with respect to th
 e local magnetic field\ndirection. Anisotropic heat conduction causes the 
 slow magnetosonic wave to become\nbuoyantly unstable to the magnetothermal
  instability (MTI) when the temperature\nincreases in the direction of gra
 vity and to the heat-flux--driven buoyancy\ninstability (HBI) when the tem
 perature decreases in the direction of gravity. The\nlocal changes in magn
 etic field strength that attend these instabilities cause\npressure anisot
 ropies that viscously damp motions parallel to the magnetic field. In\nthi
 s talk\, I will discuss two important effects of pressure anisotropy on th
 e\ndynamical and thermal stability of the ICM. First\, by stifling the\nco
 nvergence/divergence of magnetic field lines\, pressure anisotropy signifi
 cantly\naffects how the ICM interacts with the temperature gradient. Insta
 bilities which\ndepend upon the convergence/divergence of magnetic field l
 ines to generate unstable\nbuoyant motions (the HBI) are suppressed over m
 uch of the wavenumber space\, whereas\nthose which are otherwise impeded b
 y field-line convergence/divergence (the MTI) are\nstrengthened. Second\, 
 because the viscous heating of the ICM is regulated by the\npressure aniso
 tropy -- which itself is nonlinearly regulated by the plasma beta\nparamet
 er via rapidly-growing microscale instabilities -- pressure anisotropy may
 \nplay a crucial role in mitigating cooling flows and preventing cluster c
 ore\ncollapse. I will discuss the physical interpretation of these effects
  in detail\,\nplacing them within the larger context of formulating a prag
 matic analytical and\nnumerical framework for modelling astrophysical mult
 iscale plasma dynamics.\n
LOCATION:MR14\,  Centre for Mathematical Sciences\, Wilberforce Road\, Cam
 bridge
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