An electron cyclotron maser instability for astrophysical plasmas

The electron cyclotron maser instability is analyzed for a plasma which consists of a suprathermal electron component characterized by velocity-space anisotropies in directions both parallel and perpendicular to the ambient magnetic field, as well as a high-density thermal plasma in which ωe∼Ωe (where ωe and Ωe are the electron plasma and cyclotron frequencies). The complete relativistic resonance condition is used and shown to result in a ‘‘resonance ellipse’’ in momentum space. The instability is considered for both cold and warm suprathermal electron distributions, and for frequencies ω∼Ωe in the ordinary mode and ω∼2Ωe in the fast extraordinary mode. It is shown that the growth rates are comparable for these harmonics over a wide range of parameters which, since they are escape modes of the plasma, can lead to comparable radiation intensities.