Spontaneous emission of electromagnetic and electrostatic fluctuations in magnetized plasmas: Quasi-parallel modes

The present paper is devoted to the theoretical and numerical analysis of the spontaneously emitted electromagnetic fluctuations characterized by quasi-parallel wave vectors relative to the ambient magnetic field. The formulation is based upon the Klimontovich plasma kinetic theory. The comparative study is carried out between the spontaneously emitted field fluctuation spectrum constructed on the basis of a single Maxellian velocity distribution function (VDF) and the spectrum that arises from multi-component electron VDFs similar to those found in the solar wind. Typical solar wind electron VDF is composed of a Gaussian core and kappa distributions of halo and super-halo components. Of these, the halo and super-halo populations represent tenuous but energetic components. It is found that the energetic electrons make important contributions to the total emission spectrum. It is also found that the halo electrons are largely responsible for the emission spectrum in the whistler frequency range, whereas the more energetic super-halo electrons emit quasi-longitudinal fluctuations in the Langmuir frequency range, thus validating the recent quasi-steady state model of the solar wind electrons put forth by the present authors [Kim et al., Astrophys. J. 806, 32 (2015); Yoon et al., Astrophys. J. 812, 169 (2015)]. (C) 2016 AIP Publishing LLC.