Alternative high plasma beta regimes of electron heat-flux instabilities in the solar wind. (arXiv:2006.04263v2 [physics.space-ph] UPDATED)
<a href="http://arxiv.org/find/physics/1/au:+Lopez_R/0/1/0/all/0/1">R. A. López</a>, <a href="http://arxiv.org/find/physics/1/au:+Lazar_M/0/1/0/all/0/1">M. Lazar</a>, <a href="http://arxiv.org/find/physics/1/au:+Shaaban_S/0/1/0/all/0/1">S. M. Shaaban</a>, <a href="http://arxiv.org/find/physics/1/au:+Poedts_S/0/1/0/all/0/1">S. Poedts</a>, <a href="http://arxiv.org/find/physics/1/au:+Moya_P/0/1/0/all/0/1">P. S. Moya</a>
The heat transport in the solar wind is dominated by the suprathermal
electron populations, i.e., a tenuous halo and a field-aligned beam/strahl,
with high energies and antisunward drifts along the magnetic field. Their
evolution may offer plausible explanations for the rapid decrease of the heat
flux with the solar wind expansion, typically invoked being the self-generated
instabilities, or the so-called heat flux instabilities (HFIs). The present
paper provides a unified description of the full spectrum of HFIs, as
prescribed by the linear kinetic theory for high beta conditions ($beta_e gg
0.1$) and different relative drifts ($U$) of the suprathermals. HFIs of
different nature are distinguished, i.e., electromagnetic, electrostatic or
hybrid, propagating parallel or obliquely to the magnetic field, etc., as well
as their regimes of interplay (co-existence) or dominance. These alternative
regimes of HFIs complement each other and may be characteristic to different
relative drifts of suprathermal electrons and various conditions in the solar
wind, e.g., in the slow or fast winds, streaming interaction regions and
interplanetary shocks. Moreover, these results strongly suggest that heat flux
regulation may not involve only one but several HFIs, concomitantly or
successively in time. Conditions for a single, well defined instability with
major effects on the suprathermal electrons and, implicitly, the heat flux,
seem to be very limited. Whistler HFIs are more likely to occur but only for
minor drifts (as also reported by recent observations), which may explain a
modest implication in their regulation, shown already in quasilinear studies
and numerical simulations.
The heat transport in the solar wind is dominated by the suprathermal
electron populations, i.e., a tenuous halo and a field-aligned beam/strahl,
with high energies and antisunward drifts along the magnetic field. Their
evolution may offer plausible explanations for the rapid decrease of the heat
flux with the solar wind expansion, typically invoked being the self-generated
instabilities, or the so-called heat flux instabilities (HFIs). The present
paper provides a unified description of the full spectrum of HFIs, as
prescribed by the linear kinetic theory for high beta conditions ($beta_e gg
0.1$) and different relative drifts ($U$) of the suprathermals. HFIs of
different nature are distinguished, i.e., electromagnetic, electrostatic or
hybrid, propagating parallel or obliquely to the magnetic field, etc., as well
as their regimes of interplay (co-existence) or dominance. These alternative
regimes of HFIs complement each other and may be characteristic to different
relative drifts of suprathermal electrons and various conditions in the solar
wind, e.g., in the slow or fast winds, streaming interaction regions and
interplanetary shocks. Moreover, these results strongly suggest that heat flux
regulation may not involve only one but several HFIs, concomitantly or
successively in time. Conditions for a single, well defined instability with
major effects on the suprathermal electrons and, implicitly, the heat flux,
seem to be very limited. Whistler HFIs are more likely to occur but only for
minor drifts (as also reported by recent observations), which may explain a
modest implication in their regulation, shown already in quasilinear studies
and numerical simulations.
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