Excitation Characteristics of Electron Cyclotron Harmonic Waves: A Parametric Study

Abstract

The maximum growth rate, corresponding frequency, and wave normal angle of electron cyclotron harmonic (ECH) waves are investigated as functions of plasma parameters. The excitation characteristics of ECH waves are jointly controlled by hot electrons, cold electrons, and electron beams. Larger and deeper loss cones generally enhance the growth rate, while higher harmonic bands exhibit different variations compared to lower harmonic bands. The growth rate increases with hot electron density and shows harmonic‐dependent, nonmonotonic variations with parallel temperature, whereas the corresponding frequency is primarily determined by the parallel temperature. Cold electron parameters significantly affect both the growth rate and frequency of ECH waves. Electron beams generally suppress ECH waves driven by the loss cone, with particularly strong suppression occurring within a specific range of drift velocity. These results provide further insight into the excitation characteristics of ECH waves in space plasmas.