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| Titel |
Numerical simulations of electron transport in the solar wind |
| VerfasserIn |
Håkan Smith, Eckart Marsch, Per Helander |
| 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 |
250051672
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| Zusammenfassung |
| A conventional fluid approach is in general insufficient for a correct description of electron
transport in weakly collisional plasmas such as the solar wind. The classical Braginskii or
Spitzer-Härm theory is only valid when the Knudsen number (mean free path divided by
length scale of density or temperature variation) is greater than ~ 10-2. Despite this, the
classical heat transport coefficient is widely used in situations with relatively long mean free
paths. For realistic Knudsen numbers in the solar wind, the electron distribution function
develops suprathermal tails, and the departure from a local Maxwellian can be significant at
the energies which contribute the most to the heat flux moment. To accurately model this a
kinetic approach is required, and different techniques have been used previously, e.g.
particle simulations (Landi 2003), spectral methods (Pierrard 2001), the so-called 16
moment method (Lie-Svendsen 2001), and approximation by kappa functions (Dorelli
2003).
In the present study we solve the Fokker-Planck equation for electrons in one spatial
dimension and two velocity dimensions. The distribution function is solved for using a finite
element method in energy and pitch-angle, and finite differences are used in the spatial
dimension. The ion temperature and density profiles are assumed to be known, but the
electric field is calculated self-consistently to guarantee quasi-neutrality. The kinetic equation
is of a two-way diffusion type, for which the distribution of particles entering the
computational domain in both ends of the spatial dimension must be specified, leaving the
outgoing distributions to be calculated. The long mean free path of the suprathermal electrons
has the effect that the details of the boundary conditions play an important role in
determining the particle and heat fluxes as well as the electric potential drop across the
domain.
Dorelli, J.C., and Scudder, J.D. 2003, J. Geophys. Res. 108, 1294.
Landi, S., and Pantellini, F.G.E. 2003, Astron. Astrophys., 400, 769.
Lie-Svendsen, Ø., Leer, E., and Hansteen, V.H. 2001, J. Geophys. Res., 106, 8217.
Pierrard, V., Maksimovic, M., and Lemaire, J. 2001, J. Geophys. Res., 106, 29305. |
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