Stuttgart 2012 – wissenschaftliches Programm
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SYGP: Symposium Gemeinsame Probleme in Fusions- und astrophysikalischen Plasmen
SYGP 3: Contributed Talks
SYGP 3.3: Vortrag
Montag, 12. März 2012, 17:00–17:15, V55.22
Electron transport in the fast solar wind — •Håkan Smith1,2, Eckart Marsch1, and Per Helander2 — 1Max-Planck-Institut für Sonnensystemforschung, Katlenburg-Lindau — 2Max-Planck-Institut für Plasmaphysik, Greifswald
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 less than 0.01. For realistic Knudsen numbers in the solar wind, the electron distribution function develops a suprathermal tail, and the departure from a local Maxwellian can be significant at the energies which contribute the most to the heat flux moment. In the present study we solve the Fokker-Planck equation for electrons in one spatial dimension and two velocity dimensions. The equation is solved by means of a finite element method in energy and pitch-angle, and finite differences 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. It is found that the heat flux and the thermal force are both around half their respective Braginskii values. Moreover, the particle and heat fluxes are sensitive to the applied boundary condition at the outer boundary and to the ion coronal temperature profile. The heating of electrons purely by collisions with ions is inefficient because of the low collisionality. To obtain coronal electron temperatures of 1 MK one needs very hot (around 3 MK) ions.