Particle-in-cell simulations of the whistler heat-flux instability in the solar wind conditions

Abstract

In collision-poor plasmas from space, e.g., solar wind or stellar outflows, the heat-flux carried by the strahl or beaming electrons is expected to be regulated by the self-generated instabilities. Recently, simultaneous field and particle observations have indeed revealed enhanced whistler-like fluctuations in the presence of counter-beaming populations of electrons, connecting these fluctuations to the whistler heat-flux instability (WHFI). This instability is predicted only for limited conditions of electron beam-plasmas, and was not captured in numerical simulations yet. In this letter we report the first simulations of WHFI in particle-in-cell (PIC) setups, realistic for the solar wind conditions, and without temperature gradients or anisotropies to trigger the instability in the initiation phase. The velocity distributions have a complex reaction to the enhanced whistler fluctuations conditioning the instability saturation by a decrease of the relative drifts combined with induced (effective) temperature anisotropies (heating the core electrons and pitch-angle and energy scattering the strahl). These results are in good agreement with a recent quasilinear approach, and support therefore a largely accepted belief that WHFI saturates at moderate amplitudes. In anti-sunward direction the strahl becomes skewed with a pitch-angle distribution decreasing in width as electron energy increases, that seems to be characteristic to self-generated whistlers and not to small-scale turbulence.

arXiv commentAccepted for publication in ApJL

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Cited by in corpus (13)

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• On the temperature of the solar wind
• Alternative high plasma beta regimes of electron heat-flux instabilities in the solar wind
• On quasi-parallel whistler waves in the solar wind
• Electron energy partition across interplanetary shocks: III. Analysis
• Collisionless heat flux regulation via electron firehose instability in presence of a core and suprathermal population in the expanding solar wind
• Electron Temperature Anisotropy and Electron Beam Constraints From Electron Kinetic Instabilities in the Solar Wind
• Whistler instabilities from the interplay of electron anisotropies in space plasmas: A quasilinear approach
• Stability of superthermal strahl electrons in the solar wind
• Quantifying the diffusion of suprathermal electrons by whistler waves between 0.2 and 1 AU with Solar Orbiter and Parker Solar Probe
• Stochastic diffusion of electrons interacting with whistler-mode waves in the solar wind
• The aperiodic firehose instability of counter-beaming electrons in space plasmas
• Reconstruction of Polarization Properties of Whistler Waves From Two Magnetic and Two Electric Field Components: Application to Parker Solar Probe Measurements