Energetics of Triple-Nozzle Gas-Puff Z-Pinch Implosions on COBRA

We present the results of an energy-inventory analysis for argon gas-puff Z-pinch implosions driven by the 1-MA, ~230-ns rise time COBRA generator at Cornell University. Implosions with and without an applied axial magnetic field are examined. The total energy coupled to the plasma is inferred from current and voltage traces, while spatially resolved plasma parameters, such as flow velocity, temperature, and density, are measured at different times and positions across highly repeatable implosions using Thomson scattering (TS) and laser interferometry. This enables the calculation of all kinetic and internal energy components. Directed kinetic energy is also estimated from the radial implosion trajectory and initial mass distribution assuming snowplow accretion. Radiated energy is measured using a calibrated photoconducting diamond detector (PCD) and a bolometer. By including a means of discriminating between thermal and nonthermal broadening of the TS spectra, we observe features consistent with the hypothesis that small-scale turbulence mediates dissipation in a collisionless shock front. Assuming axial and azimuthal symmetry, reasonable agreement between measured and coupled energy is observed until peak current when axial nonuniformity and/or axial flux compression become significant.