Bonn 2000 – wissenschaftliches Programm

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P: Plasmaphysik

P 22: Theorie (Poster)

P 22.3: Poster

Donnerstag, 6. April 2000, 17:00–19:30, Aula

Negative electron mobilities in decaying rare-gas/halide plasmas analysed by means of a higher-order approach
— •D. Loffhagen¹, N. A. Dyatko², A. P. Napartovich², and R. Winkler¹ — ¹Institut für Niedertemperatur-Plasmaphysik, Friedrich-Ludwig-Jahn-Str. 19, 17489 Greifswald — ²Troitsk Institute for Innovation and Fusion Research, 142092 Troitsk, Russia

The topic of negative electron mobilities in low temperature plasmas has recently been studied in several papers. In particular, negative electron mobility was predicted for rare-gase plasmas containing admixtures of electron-attaching gases like F₂ and NF₃ using the conventional two-term approximation of the electron velocity distribution function (EVDF). However, if noticeable electron attachment occurs, the applicability of this approximation markedly lacks in clarity. In the present study the temporal behaviour of the EVDF and related electron swarm parameters in attachment-dominated plasmas is analysed. Using an appropriate relaxation model the time-dependent Boltzmann equation was solved in two-term approximation and multi-term approximations of the EVDF. Calculations show that the conventional two-term approach gives almost accurate results for the distribution function, density, mean energy and drift velocity of the electrons except for in the beginning of the relaxation. The EVDF finally reaches a hydrodynamic stage with time-independent attachment frequency and exponentially decreasing electron density. In some value ranges of the reduced electric field the drift velocity becomes negative in the process of the temporal evolution and even when approaching the hydrodynamic stage of the electron swarm.