Spectroscopic measurement of erosion rate on electrode surfaces of the ZaP-HD sheared-flow stabilized Z-pinch device

Plasma interactions with material surfaces introduce impurities into plasma devices that contribute to radiative losses and limit operational lifetimes. The development of a diagnostic for in-situ measurements of erosion yields is crucial for understanding impurity dynamics in plasmas, and for the evaluation of mitigation methods to minimize electrode erosion. In this work, erosion from a graphite electrode in the sheared-flow stabilized Z-pinch was investigated using optical emission spectroscopy and the ionizations per photon (S/XB) method. Measurements on the ZaP-HD device were acquired over a range of operating parameters and with multiple interchangeable copies of the graphite electrode tip. Absolute calibration using a deuterium-halogen light source enabled direct conversion to photon flux with the UV spectroscopy suite. Carbon influx in different experimental configurations was computed using the empirical S/XB coefficients, and compared to identify trends. Pulse-to-pulse variability in the plasma behavior leads to changes in the measured emission intensity and the local plasma parameters, therefore statistical analysis is needed to distinguish emission from local surface erosion.