Energetics of a long-implosion-time, 12-cm-diameter argon-gas-puff Z pinch at 6.5 MA

We carry out an energy-inventory analysis for a 12-cm-diameter, argon gas-puff shot on the Saturn generator. From the measured pinch inductance time history, we infer the average radius of the pinch current, rind, and the total work done on the pinch, Ecoupled, both as functions of time. The kinetic energy as a function of time, EKE, is inferred from rind and the measured initial mass distribution, assuming all of the mass is accreted as in a snowplow. The results show that early in the implosion, Ecoupled ≈ EKE. However, when the pinch begins to radiate significantly, EKE begins to decrease while Ecoupled continues to increase. The increase in coupled energy goes into plasma internal energy, Eint, i.e., ionization and thermal energies of the z-pinch plasma, and total radiation, Erad. During the time of K-shell emission, the significant (∼ 150-kJ) increase in Ecoupled is reflected in approximately the same increase in Erad. There is agreement between Eint at the time of peak K-shell emission inferred from Ecoupled and measurements of Erad, and Eint inferred from independent spectroscopic measurements combined with an atomic-physics model.