Sheath Effects for Electrode Research at Zap Energy

The goal of this work is to investigate the electrode sheaths in a high power Z-pinch plasma configuration. A Z pinch is one of the oldest plasma fusion configurations, but Z pinches have always suffered from a series of instabilities that limit their performance. Recently, sheared flow stabilization has resulted in significant stability gains, with some pinches lasting more than 10 us (several thousand linear instability growth times). Zap Energy is currently operating two sheared-flow-stabilized Z-pinch experiments: the Fusion Z-pinch Experiment (FuZE) and a newer, higher voltage, higher current machine, FuZE-Q. As these devices reach higher voltages and currents, the resulting plasma effects on the electrodes may play a key role in the device performance. For example, presently research conditions on FuZE are tens of kV of applied voltage that draws several hundred kA of current through a plasma with density of several times 10²³ m^-3 and temperature of several keV in a pinch of radius less than a cm. This set of parameters leads to demanding conditions on the anode and cathode. Particle-in-cell simulation offers a way to estimate the sheath size and particle flux at the anode and cathode, the plasma potential, and sputtering rate. We can examine those quantities as we vary the current emitted from the cathode, the magnetic field strength, and the amount of sputtered material.