Graphite Electrode Characterization on the ZaP-HD Sheared-Flow-Stabilized Z-Pinch Device

Applying sheared velocity flow to the Z-pinch successfully mitigates MHD instabilities, enabling the concept to scale to high energy densities on the ZaP-HD device. This provides a unique platform for studying the plasma material interactions (PMI) of the coaxial configuration in a high temperature environment for a prolonged duration. The inner electrode is exposed to the plasma while forming a part of the discharge current path, resulting in significant erosion of the tungsten-sprayed copper nose cone and contamination of the plasma. A graphite nose cone was installed to investigate its material behavior and effect on pinch performance. Plasma self-emission spectroscopy and magnetic field probes were used to identify impurities, measure ion temperature, and determine stability of the pinch. This work lays the foundation for continued study of PMI through design of a procedure for pinch characterization, an apparatus for studying candidate materials, and extensive ex-situ surface topography measurements of targets embedded in the nose cone.