Loss cone-driven cyclotron maser instability

Abstract

The weakly (or mildly) relativistic cyclotron maser instability has been successfully applied to explain the Earth's auroral kilometric radiation and other radio sources in nature and laboratory. Among the most important physical parameters that determine the instability criteria is the ratio of plasma-to-electron cyclotron frequencies, ωp/Ω. It is therefore instructive to consider how the normalized maximum growth rate, γmax/Ω, varies as a function of ωp/ Ω. Although many authors have already discussed this problem, in order to complete the analysis, one must also understand how the radiation emission angle corresponding to the maximum growth, θmax, scales with ωp/Ω, since the propagation angle determines the radiation beaming pattern. Also, the behavior of the frequency corresponding to the maximum growth rate at each harmonic, (ωmax-sΩ)/ Ω, where s=1,2,3,ċ, as a function of ωp/Ωis of importance for a complete understanding of the maser excitation. The present paper computes these additional quantities for the first time, making use of a model loss cone electron distribution function. Key Points Maser maximum growth rate vs frequency ratio has been studied before Maximum propagation angle vs frequency ratio is studied for the first time Maximum emission frequency is also studied for the first time ©2013. American Geophysical Union. All Rights Reserved.