Spontaneous whistler-cyclotron fluctuations of thermal and non-thermal electron distributions.

2020 ◽  
Author(s):  
Pablo S Moya ◽  
Daniel Hermosilla ◽  
Rodrigo López ◽  
Marian Lazar ◽  
Stefaan Poedts
Keyword(s):  
Strong Dependence ◽  
Wave Spectrum ◽  
Velocity Distribution Function ◽  
Relevant Information ◽  
Space Plasmas ◽  
Magnetic Fluctuations ◽  
Thermal Electron ◽  
Particle Distributions ◽  
Plasma State ◽  
Electron Distributions

<p>Observed particle distributions in space plasmas usually exhibit a variety of non-equilibrium features in the form of temperature anisotropies, suprathermal tails, field aligned beams, etc. The departure from thermal equilibrium provides a source for spontaneous emissions of electromagnetic fluctuations, such as whistler fluctuations at the electron scales. Analysis of these fluctuations provides relevant information about the plasma state and its macroscopic properties. Here we present a comparative analysis of spontaneous fluctuations in plasmas composed by thermal and non-thermal electron distributions. We compare 1.5D PIC simulations of a finite temperature isotropic magnetized electron–proton plasma modeled with Maxwellian and different kappa velocity distributions. Our results suggest a strong dependence between the shape of the velocity distribution function and the spontaneous magnetic fluctuations wave spectrum. This feature may be used as a proxy to identify the nature of electron populations in space plasmas  at locations where direct in-situ measurements of particle fluxes are not available.</p>

Electron Distributions in Space Plasmas

2017 ◽  
pp. 465-479 ◽  
Author(s):  
V. Pierrard ◽  
N. Meyer-Vernet
Keyword(s):  
Space Plasmas ◽  
Electron Distributions

scholarly journals Nonlinear Mirror and Weibel modes: peculiarities of quasi-linear dynamics

2010 ◽  
Vol 28 (12) ◽  
pp. 2161-2167 ◽  
Author(s):  
O. A. Pokhotelov ◽  
R. Z. Sagdeev ◽  
M. A. Balikhin ◽  
V. N. Fedun ◽  
G. I. Dudnikova
Keyword(s):  
Distribution Function ◽  
Mode Coupling ◽  
Nonlinear Evolution ◽  
Particle Interaction ◽  
Velocity Distribution Function ◽  
Larmor Radius ◽  
Initial Stage ◽  
Plasma State ◽  
Bgk Modes ◽  
Mirror Mode

Abstract. A theory for nonlinear evolution of the mirror modes near the instability threshold is developed. It is shown that during initial stage the major instability saturation is provided by the flattening of the velocity distribution function in the vicinity of small parallel ion velocities. The relaxation scenario in this case is accompanied by rapid attenuation of resonant particle interaction which is replaced by a weaker adiabatic interaction with mirror modes. The saturated plasma state can be considered as a magnetic counterpart to electrostatic BGK modes. After quasi-linear saturation a further nonlinear scenario is controlled by the mode coupling effects and nonlinear variation of the ion Larmor radius. Our analytical model is verified by relevant numerical simulations. Test particle and PIC simulations indeed show that it is a modification of distribution function at small parallel velocities that results in fading away of free energy driving the mirror mode. The similarity with resonant Weibel instability is discussed.

Whistler instability based on observed flat-top two-component electron distributions in the Earth's magnetosphere

2019 ◽  
Vol 488 (1) ◽  
pp. 954-964 ◽  
Author(s):  
M N S Qureshi ◽  
Warda Nasir ◽  
R Bruno ◽  
W Masood
Keyword(s):  
Growth Rate ◽  
Energy Transport ◽  
Hot Electrons ◽  
Electron Velocity ◽  
Space Plasmas ◽  
Earth’S Magnetosphere ◽  
Real Frequency ◽  
Earth's Magnetosphere ◽  
Electron Distributions ◽  
Two Populations

ABSTRACT One of the fundamental features of space plasmas is the observation of non-Maxwellian particle velocity distributions. In the present study, we observe electron velocity distributions in the Earth's magnetosphere at times when the electron density is low, typical of cusp values, and when it is enhanced as a result of disturbances by the solar wind. We find that electron distributions are flat-topped and have two populations: one cold and one hot. We fit the observed electron distributions by a generalized $( {r,q} )$ distribution, and derive and plot expressions for the real frequency and growth rate using fitted and observed parameters. We show that enhancement in the density of hot electrons enhances the growth rate of whistler waves, which play an important role in energy transport in the Earth's magnetosphere.

Magnetosonic solitons in space plasmas: dark or bright solitons?

2007 ◽  
Vol 73 (6) ◽  
pp. 981-992 ◽  
Author(s):  
O. A. POKHOTELOV ◽  
O.G. ONISHCHENKO ◽  
M. A. BALIKHIN ◽  
L. STENFLO ◽  
P. K. SHUKLA
Keyword(s):  
Magnetic Field ◽  
Distribution Function ◽  
Velocity Distribution Function ◽  
Mhd Equations ◽  
Space Plasmas ◽  
Ion Distribution ◽  
Loss Cone ◽  
Solitary Solution ◽  
Background Magnetic Field ◽  
The Magnetic Field

AbstractThe nonlinear theory of large-amplitude magnetosonic (MS) waves in highβ space plasmas is revisited. It is shown that solitary waves can exist in the form of ‘bright’ or ‘dark’ solitons in which the magnetic field is increased or decreased relative to the background magnetic field. This depends on the shape of the equilibrium ion distribution function. The basic parameter that controls the nonlinear structure is the wave dispersion, which can be either positive or negative. A general dispersion relation for MS waves propagating perpendicularly to the external magnetic field in a plasma with an arbitrary velocity distribution function is derived.It takes into account general plasma equilibria, such as the Dory–Guest–Harris (DGH) or Kennel–Ashour-Abdalla (KA) loss-cone equilibria, as well as distributions with a power-law velocity dependence that can be modelled by κdistributions. It is shown that in a bi-Maxwellian plasma the dispersion is negative, i.e. the phase velocity decreases with an increase of the wavenumber. This means that the solitary solution in this case has the form of a ‘bright’ soliton with the magnetic field increased. On the contrary, in some non-Maxwellian plasmas, such as those with ring-type ion distributions or DGH plasmas, the solitary solution may have the form of a magnetic hole. The results of similar investigations based on nonlinear Hall–MHD equations are reviewed. The relevance of our theoretical results to existing satellite wave observations is outlined.

scholarly journals Kappa Distributions: Statistical Physics and Thermodynamics of Space and Astrophysical Plasmas

Universe ◽  
2018 ◽  
Vol 4 (12) ◽  
pp. 144 ◽  
Author(s):  
George Livadiotis
Keyword(s):  
First Principles ◽  
Statistical Physics ◽  
Order Differential Equation ◽  
Canonical Ensemble ◽  
Space Plasmas ◽  
Astrophysical Plasmas ◽  
Particle Distributions ◽  
First Order ◽  
Continuous Description ◽  
Kappa Distribution Function

Kappa distributions received impetus as they provide efficient modelling of the observed particle distributions in space and astrophysical plasmas throughout the heliosphere. This paper presents (i) the connection of kappa distributions with statistical mechanics, by maximizing the associated q-entropy under the constraints of the canonical ensemble within the framework of continuous description; (ii) the derivation of q-entropy from first principles that characterize space plasmas, the additivity of energy, and entropy; and (iii) the derivation of the characteristic first order differential equation, whose solution is the kappa distribution function.

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