EMEC instability based on kappa-Maxwellian distributed trapped electrons in auroral plasma

Abstract

In space plasmas, particle distributions are often observed having high energy tails and are well fitted by kappa distribution function. However, in auroral region electrons are expected to be accelerated mainly along the magnetic field lines and one may expect Maxwellian behaviour in perpendicular direction. Therefore, in the present study propagation characteristics of electromagnetic electron cyclotron (EMEC) waves is studied by employing kappa-Maxwellian distribution function for energetic trapped electrons in auroral region. Real frequency and the growth rate expressions have been solved numerically for kappa-Maxwellian plasma and then analyzed by considering the effect of different plasma parameters for wide range of auroral altitudes. The numerical results obtained show that growth rate increases with the increase in ratio ${\omega_{pe}} / {\varOmega_{e}}$, plasma beta, temperature anisotropy ${T_{\bot}} / {T_{\parallel}}$ and trapped electron drift speed but decreases when superthermal electron population increases.