Cathode spot development on a bulk cathode in a vacuum arc

This work considers transient spot development on a bulk cathode, taking into account the initial adjacent plasma generated during arc triggering. A self-consistent model was developed to describe the transient cathode phenomena and the time dependent cathode potential drop, taking into account the kinetics and gasdynamics of cathode plasma flow. The time dependent spot parameters were calculated with life time τ of initial plasmas in the range of 2-100 ns for 10 A spot current for Cu, Cr & W. For Cu the cathode temperature increased from 3500 to 4600 K, while the cathode potential drop decreased from 100-45 V (depending on τ) in the initial stage to 12 V at steady state. The solution for a refractory W cathode was obtained using a previously developed virtual cathode model. Calculation shows that a spot current density of about 10⁷ A/cm² can support the spot initiation in a time of 2 ns.