Effect of suprathermal particles on EMEC instability in kappa-Maxwellian distributed space plasmas

Abstract

The present study reveals the role of suprathermal particles on the destabilization of EMEC instability modelled by kappa-Maxwellian distribution and the results are compared with bi-Maxwellian results. Presence of suprathermal particles in the velocity distribution functions indicates the highly nonthermal state of plasma having large amount of free energy which is expected to enhance the kinetic instabilities. However, most of the studies on EMEC waves using bi-kappa model showed the inhibiting effect of suprathermal particles on the instability. To address this effect in kappa-Maxwellian plasmas, following Lazar et al. (2015), we proposed two variants of kappa-Maxwellian model to investigate the role of suprathermal particles on the EMEC instability in kappa-Maxwellian plasma. In kappa-Maxwellian Model-I, kappa and Maxwellian temperatures are considered to be constant while thermal velocity for kappa is taken larger than Maxwellian thermal velocity. In kappa-Maxwellian Model-II, thermal velocities for kappa and Maxwellian are considered constant while kappa temperature is taken larger than the Maxwellian temperature. We found that growth rate of EMEC waves based on the Model-I remains larger but for Model-II remains smaller than the Maxwellian growth rate. Thus in kappa-Maxwellian plasmas the Model-I truly depicted the role of suprathermal particles in enhancing the EMEC instability in contrast to bi-kappa plasmas.