Experimental characterization of vacuum arc instabilities for different electrode material

Arc voltages and instabilities of low current DC vacuum arcs, less than 30A, which were ignited by the opening of the electrodes, were Investigated for eight kinds of electrode materials. The DC components of the arc voltages showed peculiar values to the materials but frequent spike voltages appeared together with the decrease of the arc current (instability). The intensity of the instability differed depend on the electrode material and it was confirmed that the waveform of the spike voltage was the same with the voltage drop of the inductive resistance of the circuit. The spike voltage may ignite an oscillation of the arc current as a result of L-C resonance of the circuit. The oscillations were observed by adding a parallel capacitance and a series inductance to the circuit and the waveforms of the oscillation agreed well with the simulated waveforms.