Optical Diagnostics of Vacuum Arc Discharges for Switching Applications

The contribution presents several optical diagnostics methods, which can be used for determination of such important parameters as arc plasma temperature, anode surface temperature, densities of plasma species during the current pulse and after current termination. Especially, the influence of the anode activity (various high-current anode modes) on the properties of vacuum arc plasma has been studied. The vacuum arcs have been investigated under typical switching conditions - ignition by CuCr contact separation during the AC current flow at several kA magnitude. High-speed cinematography was used for observation of arc dynamics and characterization of the anode activity. Optical emission spectroscopy (imaging, high-speed) has been applied for determination of temporal dynamics of copper spectral lines from various plasma species - atoms, ions and electrons during the active phase, as well as for determination of plasma temperature. Several methods have been used for quantitative characterization of the anode surface temperature: NIR spectroscopy and high-speed camera techniques enhanced by narrow-band filters. Broad band absorption spectroscopy is a suitable technique for determination of the vapour density close to the current zero crossing and in the early post-arc phase. The corresponding values for the Cr ground state density are presented.