Langmuir probes in switching vacuum arc measurements

Abstract

Some properties of the Langmuir probes used in measurements of electron parameters in a vacuum switching arc were tested experimentally and 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 sawtooth potential, as well as with a constant one. The arc current was a sine half-wave generated in an oscillatory low-voltage circuit, with amplitudes set from 400 A up to 1400 A with frequency of about 30 Hz. These parameters are representative for a low-voltage vacuum switching arc. The arc frequency, lower than the frequency in power network, was chosen in order to simulate both the alternating current, as well as a short duration direct current arc. The electron parameters temperature, thermal velocity, and density, were estimated. The statistical distribution of results and its accuracy was analyzed and discussed in order to observe the relation between various probe shapes, shielding conditions and the probe distance from the arcing contacts. The significant parameters, discussed in the paper, are relations between probe area and the probe distance from the arc and current densities of the probe and that of the arc. Finally, some criteria, which can be useful at application of Langmuir probes to measurements of the low-voltage vacuum arc plasma parameters were proposed.