Electron Cyclotron Harmonic Wave Instability by Loss Cone Distribution

Abstract

AbstractWe propose a new method to construct a controllable and quantifiable loss cone distribution. Then, we derive a linear growth rate formula of the electrostatic mode for a realistic and arbitrary distribution function. Such formula is used to perform a parametric study of instability analysis of the electron cyclotron harmonic (ECH) wave in a plasma consisting of electron loss cone distribution and isotropic cold electron distribution. We find (1) the peak linear growth rate and the corresponding wave frequency increase with the loss cone size. The wave frequency of peak growth rate is about 1.5 and 2.5 times electron cyclotron frequency when loss cone is about 4–6° wide. The wave normal angle corresponding to the growth rate peak decreases with the loss cone size. (2) Increasing hot electron temperature anisotropy decreases the growth rate but hardly changes the wave frequency and wave normal angle corresponding to the growth rate peak. (3) Increasing hot electron parallel temperature tends to increase both the peak growth rate and wave normal angle but only change the corresponding wave frequency slightly. (4) The peak growth rate and its corresponding wave frequency increase with ωpe/|Ωe| for wavebands above or passing upper hybrid resonance frequency ωUHR and almost remain unchanged for wavebands below ωUHR. (5) Increasing cold electron temperature tends to decrease wave frequency and increase wave normal angle and peak growth rate for wavebands below ωUHR. The impact of our work on ECH wave generation and the significance of ECH waves on diffuse aurora are also discussed.