On the stability of obliquely propagating whistlers

By means of an energy conservation approach, this paper analyzes the growth rates of whistlers with arbitrary frequency and direction of propagation in a cold plasma permeated by a dilute energetic electron population. Numerical results are obtained for whistler frequencies and plasma characteristics prevailing at the onset of artificially stimulated emissions (ω/Ω ∼ 0.5, ωp/Ω ∼ 10, the energetic electron population with varying energy and pitch angle). It is found that the growth rates do not in general maximize for propagation along the static magnetic field, and a criterion for the existence of maximal growth at this direction is derived. An application to artificially stimulated emissions is discussed.