Journal
ASTROPHYSICAL JOURNAL LETTERS
Volume 882, Issue 1, Pages -Publisher
IOP Publishing Ltd
DOI: 10.3847/2041-8213/ab398b
Keywords
methods: numerical; plasmas; solar wind; waves; instabilities; interplanetary medium
Categories
Funding
- DFG-German Research Foundation [SCHL.201/35-1]
- KU Leuven [GOA/2015-014]
- FWO-Vlaanderen [G0A2316N]
- ESA Prodex 9 [C.90347]
- FWO Postdoctoral Fellowship [12Z6218N]
- BK21 Plus program from NRF Korea
- NASA [NNH18ZDA001N-HSR]
- NSF [1842643]
- Research Foundation Flanders (FWO)
- Flemish Government-department EWI
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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 has not yet been captured in numerical simulations. In this Letter we report the first simulations of WHFI in particle-in-cell 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 the anti-sunward direction the strahl becomes skewed with a pitch-angle distribution decreasing in width as electron energy increases, which seems to be characteristic of self-generated whistlers and not to small-scale turbulence.
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