Düsseldorf 2007 – scientific programme

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P: Fachverband Plasmaphysik

P 16: Poster

P 16.6: Poster

Wednesday, March 21, 2007, 16:30–18:30, Poster A

Langmuir Probe Measurement of Plasma Parameter in a Magnetised Hollow Cathode Arc — •Attila Schröder, Gonzalo Avaria, Mahmud Shakhatre, and Achim Lunk — Institut für Plasmaforschung, Universität Stuttgart, Pfaffenwaldring 31, 70569 Stuttgart

The hollow cathode arc (HCA) is characterised by high ion densities at low electron temperatures. In the low pressure regime ionisation degrees of about several 10% can be obtained. In the neighbourhood of the cathode the isotropic plasma is superimposed by an electron beam which kinetic energy ranges from 10 eV to 30 eV depending on gas composition used. The contribution deals with Langmuir probe measurements in a magnetised HCA in comparison to measurements without magnetic fields. The magnetic field is oriented parallel to the axis of the cathode. Therefore the field acts perpendicular to cathode processes in the active zone and longitudinal to the processes in the so called inner positive column. The magnetic field strength is negligible at the places where the Langmuir probes were localised. Measurements show that ion density increases linearly with current. The form of the electron energy distribution function evaluated from probe characteristics differs from Maxwellian one and can be approximated by Dryvesteyn-distribution. The mean kinetic energy of the electrons in dependence on current remains constant and depends only on pressure or gas flow rate. The main differences between magnetised and unmagnetised plasma will be discussed within the scope of gyrating electrons inside of the hollow cathode.