Effect of a cold-plasma component on the stability of an inhomogeneous hot plasma

Abstract

By applying geometrical optics, the author investigates the effect of a volume component of cold plasma on the low-frequency oscillation spectrum and on the local stability conditions of an inhomogeneous hot plasma contained by a strong magnetic field. Allowance is made for the curvature of the lines of force of the containing magnetic field by introducing an effective gravitational field. The author points to the existence in such a system of a low-frequency oscillation branch, that is “electron” sound, with a frequency proportional to the square root of the ratio of hot to cold plasma densities. For very low cold-plasma densities a hydrodynamic growth of long-wave and short-wave oscillations of the inhomogeneous plasma results from the excitation of an “electron-acoustic” oscillation branch by the gravitational drift of the ions. For higher cold-plasma densities one observes a resonant growth of low-frequency plasma oscillations with frequencies approaching those of the diamagnetic particle drift. Further increases in the cold-plasma density such that the frequency of the electron sound exceeds all the drift frequencies of the plasma lead to an expansion of the stability region of the inhomogeneous plasma.