Cathode-Spot Dynamics in a High-Current Pulsed Arc: A Noise Study

Cathode spots are the locus for plasma production in cathodic vacuum arcs, and measurements of the discharge voltage provide information about the physics. The voltage noise and cathode-erosion patterns of a high-current pulsed titanium arc were studied as a function of time, current, and pulse shape. Enhanced noise and a 1/f³ trend in the spectral power density were observed when cathode spots are close together at the initiation of an arc for fast rising currents (>1.3 kA in 30 mus) or when the total current exceeds a threshold value of 1.6 kA. We propose a model in which the individual currents associated with the spot substructure can act as noise generators coupled via magnetic fields or coherent spot nucleation.