Asymptotic Theory of Solar Wind Electron Halo Distribution

Abstract:

The solar wind electrons are conveniently divided into core Maxwellian background, isotropic halo, and super-halo components (and some times, highly field-aligned strahl component, which can be considered as a fourth element). Recently, a theory was proposed that explains the origin of super-halo distribution. It was assumed that the super-halo distribution forms as a result of wave-particle interaction between the super-halo electron and steady-state Langmuir fluctuation known as the quasi-thermal noise. In the present paper, we discuss a theory of solar wind halo electron distribution. It is assumed that the solar wind electrons whose energy is intermediate to the Gaussian cold core and super-halo components can interact efficiently with the whistler turbulence, which is pervasively detected in the solar wind near 1 AU. By making use of Fokker-Planck particle kinetic equations for the electrons and the wave kinetic equation for the whistler waves, it is shown that the solar wind halo distribution emerges as an asymptotic steady-state solution. The figure shown below summarizes the theoretical reconstruction of the total solar wind electron velocity distribution.