The Magnetothermal Instability (MTI) is an instability that operates in dilute, magnetized astrophysical plasmas. In these plasmas, transport of heat and momentum occurs essentially exclusively along magnetic field lines, not across them. As a result, the Bragiinski term for electron thermal transport must be used to supplement the traditional magnetohydrodynamic (MHD) equations. By including electron heat transport, the traditional condition for stability in a gravitationally bound plasma, the Schwarzschild criterion, is significantly modified. The new criterion shows that for dynamically weak magnetic fields, any plasma with a downwardly increasing temperature is unstable!
In the reference below, a dispersion relation is derived in the linear regime. In our paper above, we use the ATHENA MHD code to follow the evolution of the instability into the non-linear regime and estimate its effective heat transport.
There are two MPEG movies of the Magnetothermal Instability below. The geometry is 2D with boundary conditions that are essentially reflecting in the direction parallel to gravity and periodic in the direction orthogonal to gravity. For these two movies Dirichlet boundary conditions are implemented on the temperature, that is the temperature is held constant on the walls at the top and the bottom of the simulation domain. Initial conditions are random multimode perturbations and a sinusoidal magnetic field profile such that the domain contains zero net flux.