Influence of electron nongyrotropy and anisotropy on parallel wave propagation: Numerical solution of dispersion relation

This work investigates the influence of a nongyrotropic electron beam on the coupling between the electromagnetic modes of parallel propagation in a background gyrotropic plasma. We explore the importance of the relevant parameters in driving instabilities: the ratio of electron plasma frequency to electron cyclotron frequency, the gyrophase angle, and the temperature anisotropy. We confirm previous results that nongyrotropy can lead to mode coupling for specific values of relevant parameters. More important was to observe that when the anisotropy in the system provides sufficient free energy to start instabilities, the electron nongyrotropy plays an important role to change the growth rate. ► The electron nongyrotropy could lead to electrostatic mode coupling. ► The stability does not depend on the detailed azimuthal spacing. ► The growth rates change as a function of the azimuthal angle. ► Small anisotropy on thermal velocities is sufficient to start instability.