Axial Evolution of a Sheared-Flow-Stabilized Z Pinch

Abstract

The Fusion Z-pinch Experiment (FuZE) is a sheared-flow-stabilized Z pinch based on the ZaP and ZaP-HD experiments. The FuZE device generates neutron-producing, 50-cm-long Z pinches formed from plasma accelerated through coaxial electrodes. The Z pinches are sustained between a nose cone at the tip of the plasma gun and an end wall at the end of the assembly region flux conserver. The end wall geometry is modified from a central hole to a spoked design and it is found that plasma exhaust is limited, but can be increased by increasing the ratio of ram and thermal pressures to the magnetic field pressure. The limited plasma exhaust results in a stagnation wave in the assembly region, increasing the plasma axial current and changing the shear flow profiles from a hollow to a peaked velocity distribution. The instantaneous neutron scaling with pinch current is investigated and it is found that the scaling corresponds to an adiabatic pinch where linear density increases with axial current. Lastly, the termination of plasma acceleration is found to be triggered by a blow-by instability starting at the insulator located at the breech end of the coaxial accelerator.