Characterizing the Plasma Exhaust Plume from a Sheared-Flow Stabilized Z-Pinch

Abstract

A plasma Z-pinch has often been overlooked as a method for magnetic confinement fusion due to instabilities. Using sheared-flow to stabilize the Z-pinch extends its life to where it is a plausible solution for fusion and an attractive possibility for fusion-based space propulsion. To investigate this, the plasma plume of the Fusion Z Pinch Experiment (FuZE) at the University of Washington is characterized using ion Doppler spectroscopy and quadruple Langmuir probe measurements. During pulses, signals characteristic of discharge arcs driven by quadruple probe bias capacitors are observed on probe tips at a probability proportional to the bias voltage. Quadruple probe measurements show average electron temperatures of 14.4 ± 7.8 eV that are approximately constant over the plasma and peak densities of 9.5 × 1020 ± 3.4 × 1020 m−3 that fall off nearly linearly as radius increases, suggesting a collimated plasma plume. EMI noise in quadruple probe voltage measurements prevents more accurate determinations of parameters. Spectroscopy reveals plasma velocities of 86.2 ± 2.8 km/s, while significant EMI noise and suspected unreliability preclude velocity measurements from the Mach probe. A hypothetical space thruster built with these parameters would have a specific impulse of 8790 ± 290 s and a Thrust of 1420 ± 260 N, performance significantly better than current-day electromagnetic thrusters.