Characterization of a Plasma Opening Switch Source by Interferometry and Probe Measurements

The Triggered Plasma Opening Switch (TPOS) at SNL is a unique device that exploits the high conductivity and low mass properties of plasma. The TPOS's objective is to take an initial $\sim $0.8MA ($\sim $250ns rise time) storage inductor current and deliver $\sim $0.5MA at $\sim $2.4MV ($\sim $10ns rise time) to a load of $\sim $5-10$\Omega $. Configuration advantages include low current jitter and resistive voltage drop, power gain, and minimization of trigger input power as the result of using two stages in series. This two-stage design is novel and is the first to demonstrate operation of magnetically triggered stages. Study of TPOS characteristics is in progress via an offline interferometer diagnostic; specifically, a CO$_{2 } $laser interferometer will be used to make density measurements of the source plasma. It is thought that the gross plasma source density is $\sim $10$^{14}$ cm$^{-3}$, but details of the spatial structure and temporal evolution have not previously been studied. In order to better understand switch operation, these details are essential. A double-tip Langmuir probe will also be used to provide an independent measure of plasma density and electron temperature. Current results from the interferometer using a single radial chord will be presented, along with multi-point radial measurements from the Langmuir probe.