Events associated with the rapid commutation of the current in a diffuse vacuum arc are explored experimentally and analytically in the short interval during which the current is brought to zero and the recovery voltage is established across the residual plasma. A brief pause of the order of 100 ns is observed between the passage of current through zero and the point where the recovery voltage starts to rise. Current zero is interpreted as the instant when the ion and electron currents are equal. During the subsequent pause the electrons are brought to rest and only then does a positive ion sheath develop, allowing voltage to build up across it. The charge remaining in the gap at current zero is observed to depend on the initial steady-state current and the rate at which the current is ramped to zero. Qualitative agreement is obtained by analysis, but the decay of the charge residue appears to be more rapid than the analysis predicts.

A theoretical model for current interruption in a diffuse vacuum arc with dc commutation is described. Before current zero the interelectrode plasma is modeled as an ion-neutral fluid through which electrons are flowing. After current zero a positive ion sheath grows into the plasma from the former anode, driven by the transient recovery voltage. Using the basic laws of conservation, the decay of ...