Effect of Electrode Geometry on Plasma Exhaust and Pinch Properties in the ZaP-HD Sheared-Flow-Stabilized Z-Pinch Device

The sheared-flow-stabilized (SFS) Z Pinch has been identified as a promising approach to creating thermonuclear fusion [Shumlak, J. Appl. Phys. 127 (2020)]. The axial flow mitigates the MHD instabilities producing long-lived magnetically confined plasmas. This flowing plasma impacts the end wall electrode, whose geometry affects the plasma exhaust and Z-pinch plasma properties. End wall electrode geometries with exhaust ports reduce plasma stagnation and facilitate plasma detachment from the magnetic field [Claveau et al. Phys. Plasmas 27 (2020)]. The effect of electrode geometry is experimentally investigated by operating the ZaP-HD SFS Z-pinch device with different end wall electrodes. The exhaust plasma is characterized with a moveable Langmuir probe and ion Doppler spectroscopy. Impacts on the magnetic topology and stability of the Z-pinch plasma properties are studied using axially and azimuthally distributed magnetic field probes. Three geometries are tested: small central exhaust port, four large spoked exhaust ports, and no end wall electrode. A direction for end wall geometry optimization is determined through comparison of the quiescent lifetime of the plasma during peak current drive.