Experiments and Modeling of Current Sheet Dynamics in a Coaxial Plasma Accelerator on the FuZE Experiment

The FuZE experiment produces sheared-flow stabilized Z-pinch plasmas with lifetimes of 10s of μs, ~keV ion temperatures, and densities of ~10¹⁶-10¹⁷ cm^-3. FuZE consists of a 1-m coaxial plasma accelerator that injects plasma into a 0.5 m long assembly region, where a pinch is formed with an embedded axial flow. Since pinch lifetime is set by the duration of plasma flow from the accelerator, maximizing the latter is desired. The structure of the current sheet is reconstructed from a longitudinal magnetic probe array that measures the azimuthal magnetic field profile B(z,t) with 5-cm spatial resolution. The initial snowplow phase of the current sheet is well-described by a 1D resistive MHD model. The calculated plasma density, velocity, and temperature profiles are compared to available experimental measurements. The deflagration phase of the discharge in the accelerator, which is responsible for long-duration plasma injection into the assembly region, is not captured by the simple MHD model. Several hypotheses to explain the deflagration mode are analyzed, including impedance mismatch between the accelerator channel and the assembly region, and complex plasma-neutral interaction effects, such as charge exchange.