Microsecond-conduction-time POS experiments

Experiments have been performed to improve the understanding of the μs-conduction-time plasma opening switch (POS). Measurements with a He-Ne laser interferometer show that the line-integrated plasma density reaches a peak value during conduction, then decreases to a relatively small value before opening begins. During opening, the density is low over a large fraction of the electrode gap, but is relatively high at both electrodes, indicating that opening actually occurs in the middle of the electrode gap. The dependence of conduction current and conduction time on density and other POS parameters (radius, length, and current waveform) indicate that conduction is controlled by hydrodynamic displacement and distortion of the plasma, resulting in a low density region where opening occurs, possibly by erosion. Experiments with electron-beam diode loads have been performed for a variety of load and POS configurations. Assuming the POS gap at peak power equals the radial extent of the electron orbits, the calculated switch gap is about 2-3 mm over a wide range of load impedances, conduction currents, and center conductor radii. Increased load power requires increasing the (effective) gap size. Fluid and PIC codes may be suitable to simulate the conduction and opening phases, respectively, and a combined fluid/particle model could indicate promising methods for increasing the output power using a POS.