Proton firehose instability: An interplay of thermal core and non-thermal halo protons

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.