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P: Fachverband Plasmaphysik
P 6: Theory and Modelling
P 6.5: Vortrag
Montag, 17. März 2014, 17:30–17:45, SPA HS202
Revision of the Coulomb logarithm in the ideal plasma — •Peter Mulser1, Gernot Alber1, and Masakatsu Murakami2 — 1Institut für Angewandte Physik, TU Darmstadt, Hochschulstr. 6, 64289 Darmstadt — 2Institute of Laser Engineering (ILE), Osaka University, Yamada kami, Osaka, Japan
The standard picture of the Coulomb logarithm in the ideal plasma is controversial and self-contradictory, the arguments for the lower cut off need revision. The two cases of far subthermal and of far superthermal electron drift motions are accessible to a rigorous analytical treatment. We show that the lower cut off b_min is a function of symmetry and shape of the shielding cloud, it is not universal. In the subthermal case shielding is spherical and b_min is to be identified with the de Broglie wavelength; at superthermal drift the shielding cloud exhibits cylindrical (axial) symmetry and b_min is the classical parameter of perpendicular deflection. In both situations the cut offs are determined by the electron-ion encounters at large collision parameters. This is in net contrast to the governing standard meaning that attributes b_min to the Coulomb singularity at vanishing collision parameters b and, consequently, assigns it universal validity. The origin of the contradictions in the traditional picture is analyzed.