Asymptotic theory of solar wind electrons

The solar wind electrons are conveniently divided into the core Maxwellian background, isotropic halo, and super-halo compoents (and sometimes, highly field-aligned strahl component, which can be considered as a fourth component). Recently, a theory was proposed to explain the origin of the super-halo electron distribution¹. It was assumed that the kappa electron distribution forms as a result of wave-particle interaction between the super-halo electrons and steady-state Langmuir fluctuations, known as the quasi-thermal noise, which is pervasively detected in the space environment. In the present paper, we discuss a theory of solar wind electrons that includes both the super-halo and halo electron components. It is assumed that the solar wind electrons whose energy is intermediate to the Gaussian core and super-halo components can interact efficiently with the whistler fluctuations, which is also pervasively observed in the solar wind near 1 AU, while the high-energy super-halo electrons are assumed to resonate with the high-frequency Langmuir fluctuations. By solving the self-consistent set of particle and wave kinetic equations, it is shown that the solar wind electron velocity distribution functions and Lagmuir/whistler fluctuation intensities emerge as steady-state solutions. Comparison with observed solar wind electron velocity distributions near 1 AU during quiet time obtained via WIND and Stereo spacecraft shows that the theoretical reconstruction is in good agreement.