Interferometric measurements on a triggered plasma opening switch source

Plasma opening switches (POS) have a long history in the pulsed-power field. The key idea behind the POS is to use plasma as a high conductivity, low mass conduction channel that acts as a low impedance shunt until displaced by magnetic fields. The triggered plasma opening switch (TPOS) at Sandia National Laboratories is a unique device that exploits these plasma properties, and opens by applying a magnetic field to move the plasma on a ten-nanosecond time scale. The TPOS's objective is to take the initial ~0.8 MA (~250 ns rise time) storage inductor current and deliver ~0.5 MA at ~2.4 MV (~10 ns rise time) to a load of ~5-10 ohms. Configuration advantages include power gain (output power compared to either input power or trigger power), minimization of trigger input power as the result of using two stages in series, low output jitter, and low closed-state voltage drop. This two-stage design is novel and is the first to demonstrate command triggering of a plasma opening switch. The TPOS utilizes a set of pulsed flashboard-type plasma sources with a dipole guide magnetic field. Here we report measurements of switch plasma parameters obtained by a 120 GHz heterodyne tracking interferometer. In particular, detailed plasma dynamics as a function of azimuthal position, flashboard driving voltage, and guide magnetic field strength are shown. The switch plasma is a key factor in determining switch performance, and these measurements are part of an effort to improve switch operation through better understanding of the switch plasma source spatial and temporal behavior.