Experimental characterization of vacuum arc instabilities for different electrode metals

Arc voltages and instabilities of low-current, dc vacuum arcs, less than 30 A, ignited by the opening of electrodes were investigated for eight kinds of electrode metals. The low-current dc arcs were always unstable, but the dc components of the arc voltages showed peculiar values to the metals. The intensity of the instability differed depending 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 resistor of the circuit. The spike voltage excites an oscillation of the arc current as a result of inductance and capacitance 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 with simulated waveforms.