Whistler anisotropy instability with a cold electron component: Linear theory

Abstract

The whistler anisotropy instability is driven by an electron temperature anisotropy T ⊥ / T ∥ > 1 where ⊥ and ∥ denote directions perpendicular and parallel, respectively, to the background magnetic field B o . Here kinetic linear theory in a magnetized, homogeneous, collisionless plasma model is used to study this instability when the electron velocity distribution may be represented as the sum of a hot, anisotropic bi‐Maxwellian and a cold, isotropic component. The critical β ∥ e , the value at which the maximum growth rate of the instability changes from propagation parallel to B o to oblique propagation, decreases with increasing n c / n e , where n c is the cold electron density and n e is the total electron density. At parallel propagation the maximum growth rate increases with n c / n e up to n c / n e ≃ 0.8, but then diminishes with further increases of the relative cold electron density. Introduction of a cold electron component can reduce the hot electron anisotropy necessary to excite this instability by up to a factor of 2.