Momentum interchange between cathode-spot plasma jets and background gases and vapors and its implications on vacuum-arc anode-spot development

Expressions are developed for the momentum flux density in collimated and expanding cathode-spot plasma jets by multiplying the ion flux density by the momentum carried by individual ions. Cathode spots placed in gas background produce a hemispherical metal-vapor plasma region whose radius can be predicted by equating the plasma-jet momentum flux density with the background gas pressure. In hot anode vacuum arcs and in anode-spot vacuum arcs a vapor plume from the anode expands into the cathodic plasma. Significant expansion occurs when the anodic vapor pressure becomes comparable to the cathodic momentum flux density