Electromagnetic fluctuations of the whistler‐cyclotron and firehose instabilities in a Maxwellian and Tsallis‐kappa‐like plasma

Abstract

Observed electron velocity distributions in the Earth's magnetosphere and the solar wind exhibit a variety of nonthermal features which deviate from thermal equilibrium, for example, in the form of temperature anisotropies, suprathermal tail extensions, and field-aligned beams. The state close to thermal equilibrium and its departure from it provides a source for spontaneous emissions of electromagnetic fluctuations, such as the whistler. Here we present a comparative analysis of the electron whistler-cyclotron and firehose fluctuations based upon anisotropic plasma modeled with Maxwellian and Tsallis-kappa-like particle distributions, to explain the correspondence relationship of the magnetic fluctuations as a function of the electron temperature and thermal anisotropy in the solar wind and magnetosphere plasmas. The analysis presented here considers correlation theory of the fluctuation-dissipation theorem and the dispersion relation of transverse fluctuations, with wave vectors parallel to the uniform background magnetic field, in a finite temperature anisotropic thermal bi-Maxwellian and nonthermal Tsallis-kappa-like magnetized electron-proton plasma. Dispersion analysis and stability thresholds are derived for these thermal and nonthermal distributions using plasma and field parameters relevant to the solar wind and magnetosphere environments. Our results indicate that there is an enhancement of the fluctuations level in the case of nonthermal distributions due to the effective higher temperature and the excess of suprathermal particles. These results suggest that a comparison of the electromagnetic fluctuations due to thermal and nonthermal distributions provides a diagnostic signature by which inferences about the nature of the particle velocity distribution function can be ascertained without in situ particle measurements.

Ion and Electron κ Distribution Functions Along the Plasma Sheet

“…Indeed, the Tsallis formalism, which appeared as consequence of using nonadditive entropies, has the distribution function as the main element of the theory (Milovanov & Zelenyi, 2000;Tsallis, 1988Tsallis, , 2009. They have been successfully used, both observationally and theoretically (e.g., Navarro et al, 2015;Pierrard & Meyer-Vernet, 2017;Viñas et al, 2015;Yoon & Livadiotis, 2017), to describe particle distribution functions for velocity or energy (PEDF) 10.1029/2018GL078631 in a number of plasma environments, from the Earth's and other planets magnetospheres (Benson et al, 2013;Kirpichev et al, 2017;Viñas et al, 2005) to solar radio bursts (Cairns et al, 2017). They behave similar to the Maxwellian case for low and central energies but include a power law regime that operates toward higher energies, with a slope determined by the index.…”

Single-particle velocity distributions of collisionless, steady-state plasmas must follow superstatistics

“…Plasmas in nonequilibrium steady states sometimes follow non-Maxwellian velocity distributions, one of the most common known as Kappa distributions [1][2][3]. Properties of Kappa-distributed plasmas have been extensively studied [4][5][6][7], however their origin is still a matter of debate.…”

A statistical study of spatial distribution and source region size of chorus waves using Van Allen Probes data

“…The higher occurrence rate of chorus waves at dayside was suggested to be caused by the more homogeneous magnetic field, which lowers the threshold of the free energy drive to excite chorus (Spasojevic and Inan, 2010;Keika et al, 20 2012; Katoh and Omura, 2013;Tao et al, 2014b). Note that this threshold condition is different from that for broadband whistler mode waves (Gary, 1993;Gary and Wang, 1996;Viñas et al, 2015), since the generation of broadband whistler waves should be describable using quasilinear theory (Ossakow et al, 1972;Tao et al, 2017c). Recently, using Van Allen Probes wave observations, Li et al (2016) reported that chorus wave normal angle exhibits a bi-modal distribution, with one peak near the quasi-parallel direction and the other peak near the resonance cone.…”