A two-color pyrometer for measuring electrode surface temperature on the ZaP-HD sheared-flow-stabilized Z-pinch device

The electrodes in a sheared-flow-stabilized (SFS) Z pinch supply a large current and directly contact the high-energy density plasma. These plasma-electrode interactions are an important area of research in the context of Z-pinch fusion [Shumlak, J. Appl. Phys. (2020)]. Resistive, radiative, and particle impact heating cause melting and sublimation that contribute to erosion and limit component lifetime. While qualitative observations of erosion have been made, quantitative measurements are required to understand the erosion process and its dependence on plasma and electrode material properties. The thermal response can be characterized by measuring the electrode surface temperature. A two-color pyrometer was designed to record the black-body radiation of the graphite cathode on the ZaP-HD SFS Z-pinch device [Shumlak et al., Phys. Plasmas (2017)]. The two pyrometer channels collect light at 730 nm and 960 nm, selected to optimize sensitivity close to the graphite sublimation point around 3900 K. A time resolution of up to 1.5 $\mu s$ and total measurement duration of hundreds of milliseconds capture a typical ZaP-HD pulse (approximately 100 $\mu s$) and a significant duration after the pulse to measure late-time behavior. Details on the design, operation, and calibration of this diagnostic are presented, along with measurements from initial deployment on the ZaP-HD device.