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| Titel |
Turbulence-driven temperature anisotropy and constraining effects of the mirror instability in FLR-Landau fluid simulations |
| VerfasserIn |
Pierre-Louis Sulem, Thierry Passot, Luca Marradi, Dimitri Laveder |
| Konferenz |
EGU General Assembly 2011
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 13 (2011) |
| Datensatznummer |
250048001
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| Zusammenfassung |
| Analyzes of the distribution of the ion perpendicular to parallel temperature ratio and of the
ion parallel beta showed that temperature anisotropy in the solar wind is constrained by
oblique pressure-anisotropy-driven microinstabilities (Hellinger et al., Geophys. Res. Lett.
33, L09101, 2006; Matteini et al., Geophys. Res. Lett. 34, L20105, 2007; Bale et al., Phys.
Rev. Lett. 103, 21101, 2009). In particular, in the regimes where the perpendicular
temperature dominates, the regulating factor is provided by the mirror instability. It turns out
that this low-frequency instability (together with its quenching at small scales) can be
accurately reproduced within a fluid approach that retains ion and electron Landau damping
and ion finite Larmor radius corrections (Passot and Sulem, Phys. Plasmas 14, 082502,
2007).
We discuss, in this presentation, numerical simulations performed with this “FLR-Landau
fluid” model, for a randomly driven ion-electron plasma in various regimes. A first
observation is that, at least when the dynamics is limited to a prescribed quasi-transverse
direction, simulations can be accurately performed without adding any artificial
smoothing effect. Depending on the conditions and in particular on the initial beta, the
development of one or the other type of ion temperature anisotropies is observed. When the
perpendicular ion heating is dominant, the system stabilizes in a regime slightly above the
theoretical threshold of the mirror instability for a warm bi-Maxwellian plasma,
despite the persistent growth of the temperatures. As the effect of weak collisions
is included in the model, this distance to threshold is reduced, while the system
remains governed by the mirror dynamics. Detailed inspection of the structures in
physical space reveals, in addition to quasi-static mirror structures, the presence of
small-amplitude fast waves, secondary instabilities and resonance processes leading to the
formation of quasi-singular profiles. The heating of the electrons is also analyzed,
together with the tendency of this species to evolve towards isotropic temperatures. |
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