Towards a general quasi-linear approach for the instabilities of bi-Kappa plasmas. Whistler instability

Abstract

Kappa distributions are ubiquitous in space and astrophysical poorly collisional plasmas, such as the solar wind, suggesting that microscopic and macroscopic properties of these non-equilibrium plasmas are highly conditioned by the wave-particle interactions. The present work addresses the evolution of anisotropic bi-Kappa (or bi-$\kappa$-)distributions of electrons triggering instabilities of electromagnetic electron-cyclotron (or whistler) modes. The new quasi-linear approach proposed here includes time variations of the $\kappa$ parameter during the relaxation of temperature anisotropy. Numerical results show that $\kappa$ may increase for short interval of times at the beginning, but then decreases towards a value lower than the initial one, while the plasma beta and temperature anisotropy indicate a systematic relaxation. Our results suggest that the electromagnetic turbulence plays an important role on the suprathermalization of the plasma, ultimately lowering the parameter $\kappa$. Even though the variation of $\kappa$ is in general negative ($\Delta \kappa <0$) this variation seems to depend of the initial conditions of anisotropic electrons, which can vary very much in the inner heliosphere.

18 pages, 6 figures, accepted for publication at Plasma Physics and Controlled Fusion

References in corpus (3)

• Alternative high plasma beta regimes of electron heat-flux instabilities in the solar wind
• Whistler instability stimulated by the suprathermal electrons present in space plasmas
• Whistler instabilities from the interplay of electron anisotropies in space plasmas: A quasilinear approach

Cited by in corpus (6)

• On the Relation between Kappa Distribution Functions and the Plasma Beta Parameter in the Earth Magnetosphere: THEMIS observations
• A new low-beta regime for unstable proton firehose modes in bi-Kappa distributed plasmas
• Ponderomotive forces in unmagnetized plasmas described by Kappa distribution functions
• Spontaneous Magnetic Fluctuations and Collisionless Regulation of Turbulence in the Earth's Magnetotail
• Ponderomotive forces in magnetized non-thermal space plasmas due to cyclotron waves
• Numerical simulations of temperature anisotropy instabilities stimulated by suprathermal protons