Electrical investigation of the interaction of a dense plasma with cold electrodes in air

The magnetic blowing of an arc against a third so-called commutation electrode positioned perpendicularly to the discharge axis allowed the investigation of a reproducible interaction of the plasma with this electrode. Cathodic arc spots were ignited on the commutation electrode with a negative-biased voltage and anodic spots with a positive-biased voltage. The delay times of arc spot ignition on cathodes have been measured in atmospheric pressure air for 24 different materials of high purity and for several materials of technical quality. Thereby, these materials were ordered as a function of delay time. The cathodic arc spot ignition can be divided into two different forms, one starting with a diffuse current transfer, and the other one initiated by a constricted ignition. The distribution of these forms depends mainly on the surface structure of the cathodes. A satisfactory explanation of the results can be given by proceeding on the assumption that surface effects are dominant over the bulk properties of the material.