Aachen PK 2003 – scientific programme

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P: Plasmaphysik

P II: HV II

P II.1: Invited Talk

Tuesday, March 18, 2003, 10:30–11:00, FO2

Investigation of the mode variety of the cathodic arc attachment — •Jürgen Mentel, Oliver Langenscheidt, Stefan Lichtenberg, Lars Dabringhausen, and Marco Redwitz — Ruhr University Bochum, Fundamentals of Electrical Engineering Group, Universitätsstr. 150, 44780 Bochum, Germany

The cathodic plasma boundary layer and the electrode represent a system which is determined by the nonlinear interaction between both while the feedback of the discharge onto the cathode is only of minor importance. The consequences of these nonlinearities are different modes of arc attachment. They are investigated systematically by high speed photography and by electrical, pyrometric and spectroscopic measurements at cylindrical tungsten electrodes operated in a model lamp.

Quite different modes are observed: a diffuse mode, a spot mode and a super spot mode. The major difference between the three modes is the current density which is low in the diffuse mode (10² Acm⁻²) high in the spot mode (10⁴ Acm⁻²) and still higher in the super spot mode (10⁵ Acm⁻²). The diffuse mode is favoured by high current, low pressure and weak cooling of the electrode, the spot and the super spot mode by the opposite conditions. Moreover they are influenced by magnetic effects in the arc contraction zone in front of the cathode. The super spot mode is additionally accompanied by the formation of a microprotrusion on the electrode surface. The experimental results are compared with first attempts of a theoretical modelling.

Granted by the BMBF (Project Ref.-No 13N7763.)