Darmstadt 2008 – scientific programme

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P: Fachverband Plasmaphysik

P IV: Poster: Niedertemperaturplasmen II, Astrophysikalische Plasmen, Magnetischer Einschluss, Plasma-Wand-Wechselwirkung

P IV.15: Poster

Thursday, March 13, 2008, 16:00–18:30, Poster C2

Study of the cathode region of a helium-xenon discharge in spot mode — •Jörn Winter, Hartmut Lange, Irina A. Porokhova, Florian Sigeneger, and Detlef Loffhagen — INP Greifswald, Felix-Hausdorff-Str. 2, 17489 Greifswald

The cathode region of a dc helium-xenon discharge in spot mode has been investigated experimentally and theoretically. By means of spectroscopic measurements, the spatial profiles of the gas and the cathode surface temperatures have been determined in the vicinity of the spot in dependence on the discharge current. Furthermore, the density of resonance and metastable xenon atoms (1s₄ and 1s₅) were measured by diode laser absorption spectroscopy.

To describe theoretically the plasma in the vicinity of the spot, a two-dimensional fluid model was applied which includes the particle balance equations for electrons, ions and various kinds of excited atoms, the energy balance equation for electrons and Poisson’s equation. The required electron transport and collision rate coefficients were taken as functions of the mean electron energy and the density of excited atoms from a lookup table which was generated by solving the steady-state spatially homogeneous electron Boltzmann equation.

The modelling results indicate the broadening of the discharge from the narrow spot towards the anode which is connected with large spatial changes of the electric field in axial and radial direction including reversals of its direction. Good agreement between the calculated and measured density profiles of the excited atoms has been obtained.

The work was supported by "Deutsche Bundesstiftung Umwelt".