Linear stability of static equilibrium states in the Hall-magnetohydrodynamics model

The magnetohydrodynamic (MHD) plasma model, as modified by the Hall effect, is given a Hamiltonian formulation and its stability properties are studied. It is found that, in most cases, a stable MHD plasma remains stable after the addition of the Hall effect. The most notable exceptions are when the pressure profile decreases with increasing density or when the entropy increases with density. The Hamiltonian structure of the equations enables the derivation of bounds that restrict the location of eigenfrequencies in the complex plane in some cases. The phenomenon of overstability, whereby the real part of a marginally stable eigenfrequency does not vanish, appears to be typical.