High-Power Opening-Closing Switches Using Grid-Controlled Plasmas

Two switches are described with the capability of rapidly interrupting high-power circuits: a vacuum triode with a large-area plasma cathode, and a grid-controlled plasma conduction switch. Theoretical models for the vacuum triode imply that it could control voltages in the range ?100 kV at current density ?2 × 104 A/m2. The vacuum switch has the advantage of rapid switching at the expense of reduced efficiency because of its significant anode-cathode voltage drop. In contrast, the plasma switch has almost zero voltage in the conducting state. The theoretical models presented indicate that the plasma switch could conduct current densities in the range 10 × 104 A/m2 with open-circuit voltage ? 100 kV. Although the closing time is long (~1 ?s), the predicted opening time is short (~20 ns). Initial experiments demonstrating the principle of operation of the plasma switch are reported.