Initial Planning for Interferometry Measurements on Triggered Plasma Opening Switch Source

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 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 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 laser interferometer will be used to make density measurements of the source plasma. It is thought that the gross plasma source density is ~10¹⁴ 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. Presently two interferometer systems are planned for testing: a temporary 1 mum system for initial plasma characterization, and a 10.6 mum laser system for routine use. We will start with a single chord measurement then upgrade to a multi-chord system. Future plans involve varying plasma source parameters, such as magnetic field strength and plasma fill time, in order to understand the density dependence on these parameters. Improved knowledge of the plasma source density behavior should allow for improved switch operation.