Abstract
The ability of space plasmas to self-regulate through mechanisms involving self-generated fluctuations is a topic of high interest. This paper presents the results of a new advanced quasilinear (QL) approach for the instability of electromagnetic ion-cyclotron modes driven by the relative alpha-proton drift observed in solar wind. For an extended parametric analysis, the present QL approach includes also the effects of intrinsic anisotropic temperatures of these populations. The enhanced fluctuations contribute to an exchange of energy between proton and alpha particles, leading to important variations of the anisotropies, the proton-alpha drift and the temperature contrast. The results presented here can help understand the observational data, in particular, those revealing the local variations associated with the properties of protons and alpha particles as well as the spatial profiles in the expanding solar wind.
Highlights
In collision-poor plasmas in space, e.g., solar wind and planetary magnetospheric environments, the dynamics of plasma particles, and implicitly their macroscopic properties, are expected to be constrained by the wave turbulence and the enhanced fluctuations, which are important components of these hot and dilute plasmas [1,2,3]
Let us start by overviewing the linear wave properties associated with a plasma in which the ions are made of majority protons and alpha particles as the minor species
An advanced quasilinear (QL) analysis of the electromagnetic ioncyclotron (EMIC) instabilities, driven by the kinetic anisotropies of protons and alpha particles, i.e., their relative drift, combined with or without the intrinsic temperature anisotropies, is presented. Such plasma conditions are specific to the solar atmosphere at short heliosphere distances, in the outer corona and solar wind
Summary
In collision-poor plasmas in space, e.g., solar wind and planetary magnetospheric environments, the dynamics of plasma particles, and implicitly their macroscopic properties, are expected to be constrained by the wave turbulence and the enhanced fluctuations, which are important components of these hot and dilute plasmas [1,2,3]. The resulting enhanced fluctuations can evolve fast enough so as to affect the regulation of ion drifts and their anisotropies [10,11], but may contribute to the preferential heating of minor ions [5,12,13,14] Their number densities, and the relative proton-alpha drift are observed to decline with heliospheric distance [15,16], most probably due to scattering of the beaming particles involving self-generated instabilities. An advanced quasilinear (QL) approach of the EM ion-cyclotron (EMIC) instabilities, driven by the proton-alpha relative drifts, is presented as recently predicted by linear theory [11]. More elaborate QL diffusion theories attempting to reproduce transient deformations of the anisotropic distribution [25] are complicated and restricted far to a limited approximation of treating the wave spectral intensity as fixed and not evolving in time, which make their implementation to fully describe the saturation of the fluctuations and relaxation of the anisotropic distribution not yet feasible
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