Cathode fall measurements in a high pressure low current argon arc using Langmuir probes

Summary form only given. This work is part of investigations aiming at "Fundamental Characterization of Thermionic Cathodes". In order to verify and further develop models of the cathode boundary layer, measured values of the cathode fall are of great importance. In this paper a method is introduced with which the cathode fall can be determined from measurements of the local plasma potential in an argon model lamp by a Langmuir probe. Typical conditions are I/sub DC/=1 to 10 amps and p=1 to 6/spl times/10/sup 5/ Pa. The Langmuir probe is a diagnostic tool for measuring the local plasma potential by means of the current-voltage-characteristic of the probe. Two independent probes are used. Both probes are inserted into the same cross section of the tube. The probes consist of cylindrically bent pure tungsten wires, 0.5 mm in diameter.