Abstract
Higher levels of solar wind temperatures are reported to be constrained. Microinstabilities play a key role under dilute space plasma conditions. The present study highlights the role of proton firehose instability in defining parallel temperatures of protons. Considering reality, we chose a bi-Maxwellian model for core protons, while halo protons are best modeled with kappa distribution. Taking different sets of input parameters like temperature anisotropy, plasma beta, and kappa index into account, the growth rate levels and associated domains for an unstable firehose mode are investigated.
Highlights
Solar wind plasma is typically composed of electrons, protons, and alpha particles with a kinetic energy between 0.5 and 10 keV
By kinetic treatment of the unstable plasma, the resulting instabilities and wave fluctuations can be described by the convincing models for the velocity distribution functions (VDFs) of plasma particles
The entire distribution function can be well adjusted by superpositioning a Maxwellian core and one or more power law distributions.[6,7,8,9,10,11]
Summary
Solar wind plasma is typically composed of electrons, protons, and alpha particles with a kinetic energy between 0.5 and 10 keV. Electrons and ions gain energy either through cyclotron resonance or Landau damping of linear waves[17–21] and for large amplitude and plasma turbulance, energy is gained/lost through nonlinear Landau damping.[18,22,23] These instabilities are constrained in the magneto-active. Sarfarz et al.[26,27] investigated electron firehose instability, both in linear and quasilinear regime, assuming a two component core-halo electron plasma. Shaaban et al.,[29] have studied EMIC instability for the limit T > T∥ during the adiabatic expansion of solar wind, considering only the proton core (or thermal) populations where they just overlook the implication of suprathermal halo components. Shaaban et al.[29] highlighted the threshold conditions of electromagnetic ion cyclotron instability assuming a two component core-halo proton solar wind plasma. Our study assumes a more realistic model that comprises distinct proton core-halo population reported for the solar wind plasma.
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