Gap formation in microsecond megaampere plasma opening switches

A mechanism of the erosion gap formation in a microsecond plasma opening switch at the end of the conduction phase is proposed. For the switch current, I_s, linearly increasing at a rate Í, the voltage across the gap obeys the relation eV_s/mc² ~ (u/c)² or eV_s/mc² ~ (u/c) for low or high switch voltage, respectively. Here, u=LÍ/1_s is the average velocity of magnetic field penetration into the switch, whose axial length is L. For eV_s ~ mc², the switch resistance varies as Í^1/2, while for eV_s >;>; mc² the resistance does not depend on the current rise rate. In the practically interesting case of high voltages, the power of a system with a plasma opening switch is proportional to the product of the switch length and the current rise rate in the inductive energy store. The expressions relating the switch voltage to the switch parameters, obtained in this work, agree with the results of numerous experiments performed on various set-ups.