Linear Vlasov theory of a magnetised, thermally stratified atmosphere

Abstract

The stability of a collisionless, magnetised plasma to local convective disturbances is examined, with a focus on kinetic and finite-Larmor-radius effects. Specific application is made to the outskirts of galaxy clusters, which contain hot and tenuous plasma whose temperature increases in the direction of gravity. At long wavelengths (the "drift-kinetic" limit), we obtain the kinetic version of the magnetothermal instability (MTI) and its Alfvénic counterpart (Alfvénic MTI), which were previously discovered and analysed using a magnetofluid (i.e. Braginskii) description. At sub-ion-Larmor scales, we discover an overstability driven by the electron temperature gradient of kinetic-Alfvén drift waves -- the electron MTI (eMTI) -- whose growth rate is even larger than the standard MTI. At intermediate scales, we find that ion finite-Larmor-radius effects tend to stabilise the plasma. We discuss the physical interpretation of these instabilities in detail, and compare them both with previous work on magnetised convection in a collisional plasma and with temperature-gradient-driven drift-wave instabilities well-known to the magnetic-confinement-fusion community. The implications of having both fluid and kinetic scales simultaneously driven unstable by the same temperature gradient are briefly discussed.

51 pages, 9 figures; to appear in Journal of Plasma Physics

References in corpus (9)

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Cited by in corpus (9)

• Whistler-regulated MHD: Transport equations for electron thermal conduction in the high $\beta$ intracluster medium of galaxy clusters
• Self-sustaining sound in collisionless, high-beta plasma
• Suppressed heat conductivity in the intracluster medium: implications for the magneto-thermal instability
• Electromagnetic instabilities and plasma turbulence driven by electron-temperature gradient
• Plasma physics of the intracluster medium
• Collisionless conduction in a high-beta plasma: a collision operator for whistler turbulence
• Magneto-Thermal Instability In Galaxy Clusters II: Three-Dimensional Simulations
• Thermal conductivity with bells and whistlers: suppression of the magnetothermal instability in galaxy clusters
• Transport of electrons in tangled magnetic fields