On the MHD analogue of the Brunt-Vaisala frequency in a magnetized plasma

摘要

The MHD analogue of the Brunt-Vaisala frequency N-B, in a magnetized, ideally conducting plasma is obtained, with the vertical component of the magnetic field, B-r, taken into account. The magnetic field vector (B-r, B-theta, B-phi) is assumed to satisfy the condition B(.)delB approximate to B-r dB/dr, which holds in many cases of interest. The frequency N-B happens to depend, generally speaking, on the magnetic field orientation relative to the direction of gravity However, for an isentropic gas, the convective instability criterion is governed by the magnetic field strength (rather than by the orientation of B). In general, the magnetic field has a stabilizing (destabilizing) effect if B/rho grows (decreases) along the vertical axis r. This conclusion seems not to depend on the specific magnetic field configuration. [References: 17]