Electromagnetic cyclotron-loss-cone instability associated with weakly relativistic electrons

The amplification of fast extraordinary mode waves with frequencies very close to the electron cyclotron frequency is investigated for a plasma which consists of a weakly relativistic electron component with a loss-cone type distribution and a cold background electron component. The basic mechanism of the amplification is attributed to a relativistic cyclotron resonance between the wave and the energetic electrons. The method employed in the present analysis enables us to solve the dispersion relation in a self-consistent manner for arbitrary ratio of the densities of the energetic and background electrons. It is found that the maximum growth rates occur at certain values of #betta#2sub(pe)/ Ω2sub(e) and the angular dependence of the growth rate is sensitive to the ratios #betta#2sub(pe)/Ω2sub(e) and nsub(e)/nsub(b). Here #betta#sub(pe) and Ωsub(e) are the electron plasma frequency and the electron cyclotron frequency, respectively, and nsub(e) and nsub(b) denote the number densities of the energetic and background electrons, respectively. (author)