Drift-Wave Instabilities of a Compressional Mode in a High- β Plasma

While the ordinary electrostatic drift mode is stabilized by either high-$\ensuremath{\beta}$ effects or an admixture of cold plasma, a compressional drift mode is shown to be destabilized under these same circumstances. The condition of the instability is approximately given by $\frac{{n}_{h}}{{n}_{c}}<\frac{\ensuremath{\beta}\ensuremath{\kappa}_{0}^{}{}_{}{}^{2}\ensuremath{\rho}_{i}^{}{}_{}{}^{2}}{2}$, where ${n}_{h}$ and ${n}_{c}$ are the number densities of the hot and cold components, respectively; ${\ensuremath{\kappa}}_{0}$ is a measure of the density, temperature, or magnetic field gradients; and ${\ensuremath{\rho}}_{i}$ is the ion Larmor radius.