The role of the thermal properties of electrons on the dispersion properties of Alfvén waves in space plasmas

Abstract

Context. The transition from left-hand to right-hand polarized Alfvén waves depends on the wavenumber, the ratio of kinetic to magnetic pressure $\beta$, temperature anisotropy, and ion composition of the plasma. Along with the temperature anisotropy, the electron-to-proton temperature ratio $T_e/T_p$ is of great relevance for the characterization of the thermal properties of a plasma. This ratio varies significantly between different space plasma environments. Thus, studying how variations on this ratio affect the polarisation properties of electromagnetic waves becomes highly relevant for our understanding of the dynamics of space plasmas. Aim. We present an extensive study on the effect of the thermal properties of electrons on the behaviour and characteristics of Alfvénic waves in fully kinetic linear theory, as well as on the transition from electromagnetic ion-cyclotron (EMIC) to kinetic Alfvén waves (KAW). Method. We solve the fully kinetic dispersion relation for oblique electromagnetic waves of the Alfvén branch in a homogenous Maxwellian electron-proton plasma. We quantify the effect of the thermal properties of electrons by varying the electron-to-proton temperature ratio for different configurations of the propagation angle, ${\beta }_p=8\pi nk{T}_p/B^2$, and wavenumber. Results. We show that the temperature ratio $T_e/T_p$ has strong and non-trivial effects on the polarisation of the Alfvénic modes, especially at kinetic scales and ${\beta }_e+{\beta }_p>0.5$. We conclude that electron inertia plays an important role in the kinetic scale physics of the KAW in the warm plasma regime, and thus cannot be excluded in hybrid models for computer simulations.

13 pages, 7 figures

References in corpus (12)

• Nature of Kinetic Scale Turbulence in the Earth's Magnetosheath
• Spatial Structure and Collisionless Electron Heating in Balmer-dominated Shocks
• Relativistic Collisionless Shocks in Unmagnetized Electron-Positron Plasmas
• Comparison of the ion-to-electron temperature ratio prescription: GRMHD simulations with electron thermodynamics
• Kinetic Scale Slow Solar Wind Turbulence in the Inner Heliosphere: Co-existence of Kinetic Alfvén Waves and Alfvén Ion Cyclotron Waves
• On the temperature of the solar wind
• Electron-Ion Temperature Ratio in Astrophysical Shocks
• General dispersion properties of magnetized plasmas with drifting bi-Kappa distributions. DIS-K: DIspersion Solver for Kappa plasmas
• Mixing the solar wind proton and electron scales. Theory and 2D-PIC simulations of firehose instability
• Effects of electron drift on the collisionless damping of kinetic Alfvén waves in the solar wind
• The effect of oxygen ions on the stability and polarization of Kinetic Alfvén Waves in the Magnetosphere
• The effect of heavy ions on the dispersion properties of kinetic Alfvén waves in astrophysical plasmas