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P: Plasmaphysik

P 11: Dusty Plasmas and Low Temperature Discharges (Poster Session)

P 11.17: Poster

Donnerstag, 5. April 2001, 12:30–15:00, AT2

Langmuir probe measurements in high pressure arcs — •Jens Luhmann¹, Daniel Nandelstädt¹, Jürgen Mentel¹, and M. S. Benilov² — ¹Ruhr-University Bochum, Fundamentals of Electrical Engineering Group, Universitätsstr. 150, 44780 Bochum, Germany — ²Departamento de Física,

An arc discharge is operated in argon or xenon at a pressure of 0.1-1MPa and a dc current of 1-10A. In order to verify theoretical models for the plasma boundary layer in front of cathodes the fall voltage of pure and modified tungsten cathodes is investigated. Therefore two Langmuir probes are inserted into the arc tube to determine the plasma potential on the axis of the arc column at the position of the probe. The probes are made of thin tungsten wires shaped as half circles at their ends so that both probes form a ring which surrounds the arc. One probe is operated at floating potential, the other is connected with a voltage ramp generator which is biased against the grounded cathode. From the recorded current-voltage-characteristic the plasma potential on the axis is deduced by theoretical consideration. To verify the results of the probe measurements they are compared with those of caloric measurements. The agreement of the results achieved by the different methodes is remarkably good. It can be concluded, that the cathode voltage fall is a function of the current, the arc attachment, the gas, the cathode shape and material.
Financial support is supplied by the German Federal Ministry of Education and Research (Ref.-No. 13N7763).