Electron Kinetic Instability Driven by Electron Temperature Anisotropy and Electron Beam in the Solar Wind

Electron temperature anisotropy instabilities are believed to constrain the distributions of the electron parallel and perpendicular temperatures in the solar wind. When the electron perpendicular temperature is larger than the parallel temperature, the whistler instability is normally stronger than the electron mirror instability. While the electron parallel temperature is larger than the perpendicular temperature, the electron oblique firehose instability dominates the parallel firehose instability. Therefore, previous studies proposed the whistler and electron oblique firehose instabilities constraint on the electron dynamics in the solar wind. Based on the fact that there always exists the differential drift velocity among different electron populations, we consider the electron kinetic instability in the plasmas containing the electron anisotropic component and the electron beam component. Consequently, we give a comprehensive electron kinetic instability analysis in the solar wind. Furthermore, we propose that the electron acoustic/magneto-acoustic instability can arise in the low electron beta regime, and the whistler electron beam instability can be triggered in a wide beta regime. These two instabilities can provide a constraint on the electron beam velocity. Moreover, we find a new instability in the regime of the electron beta ~ 1, and this instability produces obliquely-propagating fast-magnetosonic/whistler waves. These results would be helpful for distinguishing the electron instability and for analyzing the constraint mechanism on the electron temperature distribution in the solar wind.