Effects of a High-Frequency Electric Field on Micro-Instabilities Driven by Density Gradient

Drift, drift-dissipative, and drift-cyclotron instabilities in an inhomogeneous plasma are considered for the case when a uniform high-frequency electric field is applied along the magnetic field. For the applied field, the dipole approximation is made and the skin effect is neglected. Without averaging the distribution function over the period of the applied electric field, the dispersion relations are derived for both the collisionless and collisional regimes. It is found that the high-frequency field whose frequency is within some ranges increasing the frequencies of perturbations can stabilize drift instabilities and also drift-cyclotron instabilities with finite k z of the fluid-type, where k z is the component of the wave vector along the magnetic field. It is found, however, that when the unstable drift-dissipative mode is stabilized the stable mode becomes unstable.