Measurements of the imploding plasma sheath in triple-nozzle gas-puff z pinches on 1-MA COBRA

The conditions of imploding gas-puff z-pinch liners are measured on the 1-MA, 220-ns COBRA generator at Cornell University for various gas species and initial densities midway through the run-in phase of the implosion. The gas-puff loads are initialized by a 7 cm diameter triple-nozzle gas valve assembly with concentric outer and inner annular nozzles and a central gas jet. A 526.5-nm, 10-J Thomson scattering diagnostic laser provides spatially resolved flow and temperature profiles at a radius of 1-1.5 cm with a resolution up to 250 μm. Laser shearing interferometry provides measurements of the local electron density while extreme ultraviolet pinhole cameras record the time evolution of the collapsing plasma column. Additional diagnostics include filtered photoconducting diodes to measure x-ray emission near stagnation. The results reveal distinct differences in velocity and temperature profiles between the various gas species at similar mass densities, as well as between identical gas species at different initial densities. In some cases, the scattered laser spectra suggest additional non-thermal broadening that is inconsistent with local velocity gradients and may be indicative of small-scale hydrodynamic motion.