Langmuir probes in switching vacuum arc measurements

Some properties of the Langmuir probes used in measurements of electron parameters in a vacuum switching arc are reported in the paper. Two shapes of the probe: plane and Faraday-cup one, placed at various distances from the arc column, were compared. Also some shields of probes were tested. Probes were supplied with a saw-tooth potential as well as with a constant one. The arc current was a sine half-wave with amplitudes from 400 A up to 1400 A, generated in an oscillatory low-voltage circuit. The electron parameters: temperature, thermal velocity and density were measured. The comparison of statistical distribution of results and its accuracy illustrate the relation between various probe shapes, shielding and the probe distance from the arcing contacts. The best accuracy of measurement was observed in case of the respective probe shielding or the proper distance between the probe and the tested vacuum arc. Finally some additional criteria, which can be useful in choosing of the Langmuir probe in measurements of the low voltage vacuum arc plasma parameters were proposed.