Magnetoplasmadynamic switch

Abstract

A magnetoplasmadynamic switch adapted to be coupled in parallel with an ictive energy storage circuit carrying current through an initially closed circuit interrupter. The switch includes an electrode spaced by a gap from an arcjet source which is triggered by a capacitor. The capacitor is connected to the arcjet source by a closing switch so that a plasma jet is created between the source and the electrode. The voltage on the capacitor is chosen such that the arcjet source current will equal the current in the energy storage circuit at the time when the circuit interrupter has completely opened. The circuit interrupter is opened after the plasma jet is established between the source and the electrode, and the energy storage circuit current is conducted by the magnetoplasmadynamic switch until the dielectric strength of the circuit interrupter reaches a satisfactory level. Another switch is then closed providing a low impedance conduction path parallel to the arcjet source current. The arc current decays with a time constant equal to the arcjet source inductance divided by its resistance (typically several microseconds). The decay of arc current disrupts the magnetoplasmadynamic force balance, cutting off the plasma jet. Plasma already in the gap, however, continues to leave at high speed reducing the density of conducting material below that needed for high conductivity, thereby opening the switch on the timescale of gap distance divided by plasma jet speed. The current from the inductive energy storage circuit is then diverted into a parallel circuit including an inductive load.