Ion and electron beam effects on kinetic Alfven wave with general loss-cone distribution function—kinetic approach

Abstract

This work studies the effect of ion and electron beam on kinetic Alfven wave (KAW) with general loss-cone distribution function. The kinetic theory has been adopted to evaluate the dispersion relation and damping rate of the wave in the presence of loss-cone distribution indices J. The variations in wave frequency ω and damping rate with perpendicular wave number k⊥ρi, (k⊥ is perpendicular wave number and ρi is ion gyroradius) and parallel wave number k|| are studied. It is found that the distribution index J and ion beam velocity enhance the wave frequency at lower k⊥ρi, whereas the electron beam velocity enhances the wave frequency at higher k⊥ρi. The calculated values of frequency correspond to the observed values in the range 0.1–4 Hz. Increase in damping rate due to higher distribution indices J and ion beam velocity is observed. The effect of electron beam is to reduce the damping rate at higher k⊥ρi. The plasma parameters appropriate to plasma sheet boundary layer are used. The results may explain the transfer of Poynting flux from the magnetosphere to the ionosphere. It is also found that in the presence of the loss-cone distribution function the ion beam becomes a sensitive parameter to reduce the Poynting flux of KAW propagating towards the ionosphere.