Effect of suprathermal particles on EMEC instability in kappa-Maxwellian distributed space plasmas
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ORIGINAL ARTICLE
Effect of suprathermal particles on EMEC instability in kappa-Maxwellian distributed space plasmas M. Nazeer1 · M.N.S. Qureshi1
· H.A. Shah2 · C. Shen3
Received: 18 February 2020 / Accepted: 6 August 2020 © Springer Nature B.V. 2020
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 kappaMaxwellian 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.
B M.N.S. Qureshi
[email protected]
1
Department of Physics, GC University, Lahore, 54000, Pakistan
2
Department of Physics, FC College (A Charted University), Lahore, Pakistan
3
Shenzhen Graduate School, HIT Campus, University Town of Shenzhen, Shenzhen, P.R. China
Keywords Kappa-Maxwellin distribution · EMEC waves · Effect of suprathermal particles · Kappa distribution function
1 Introduction In many space plasmas, the suprathermal populations are the prevalent feature of solar wind, magnetospheric and auroral plasmas. Many physical scenarios such as absence of interactions and strong radiations in astrophysical plasmas, lack of collisions in solar wind and presence of parallel electric fields in auroral plasma are the robust causes for the presence of energetic/suprathermal particles in the profile of velocity distributions (Lazar et al. 2015 and references therein). The presence of such suprathermal particles are the manifestation of the deviation of plasma from thermal equilibrium. Direct observations of solar wind plasma verify this fact by providing evidence for the departure from a Maxwellian distribution and also point towards the cause of this deviation (Marsch 2006). Such nonthermal states depicted by particle velocity distributions are reflected by the presence of temperature anisotropy in the distribution and abundanc
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