: Optical emission spectroscopy is employed to characterize the plasma in the NRL torch operating at approx. 100 kW DC power. Both non-transferred and transferred arc configurations are considered. The working gas of the torch is nitrogen with a 5% admixture of hydrogen. Atomic emission lines are measured and analyzed using a local thermodynamic equilibrium (LTE) and a collisional radiative equilibrium (CRE) model. The core of the arc is found to be close to LTE, with a central plasma temperature of 6,200 deg K in the non-transferred mode, and approx. 15,000 deg K in the transferred mode. However, the periphery of the arc is far from thermal and excitation equilibrium. Radiative photo-pumping by the hot core, included in the CRE model, is found to play a significant role in controlling excited level populations. Stark broadened H sub Beta measurements of the non-transferred arc indicate an anomalously high electron density. For the transferred arc the plasma radiation accounts for approx. 50% of the energy input to the plasma. Finally, the electrical properties of long transferred arcs are found to change during slag processing due to entrainment of volatized slag material with low ionization potential. This suggests an on-line diagnostic for the process state of the treated waste.

A systems study of the power flow coupling between the multi-modular, inductive energy store DECADE-QUAD generator and an imploding z-pinch load is investigated and discussed. An end-to-end numerical simulation for the transmission line generator, the plasma opening switch, and the dynamic load is applied to predict the inductive notch of the load current, the kinetic energy coupling, and the radiation yield arising from argon puff gas implosions. Predicted load performance is evaluated using a I-D non-LTE radiation transport treatment self consistently coupled to the MHD model and circuit power flow. The loads are configured as shells, uniform fills, and structured density profiles. The latter profiles are chosen for their stability during run-in as determined by 2-D MHD numerical simulations. Various models of the switch behavior are studied and their impact on the load dynamics. The radiative performance from an argon puff gas will be determined as a function of switch model, mass loading, and initial pinch radius.

The radiative behavior and its influence on the energy redistribution of a dynamically imploding current driven krypton gas puff plasma is investigated. Time dependent radiation magnetohydrodynamic numerical simulations self-consistently driven by a circuit equation are carried out for loads that remain stable to the Rayleigh-Taylor instability. The circuit driving the load is represented by a superclass pulsed power generator with peak short circuit currents of between 60 and 100 mega-amperes. The loads are configured either as thin annular cylindrical shells or uniform cylindrical fills. The results suggest a class of load designs leading to higher density on axis that may produce enhanced K-shell yields.

Summary form only given, as follows. In this study we investigate and assess the radiative potential of a superclass pulsed power driven Z-pinch plasma load. The generator is represented by a driver capable of producing short circuit currents of 60, 80, and 100 mega-amps to a load over 100 ns current risetime. For a prescribed set of electrical characteristics we will characterize the radiative performance of Rayleigh-Taylor stable loads. The purpose of this investigation is to compare and contrast the differences resulting from: (1) two temperatures vs. one temperature and (2) a time dependent vs. an equilibrium treatment of the non-LTE ionization physics and their influence on the G and K-shell dynamics and how they influence the K-shell yield for krypton loads. The loads are represented as either 3 cm radius annular shells or uniform fills of 3, 5, and 7 cm radius and 3 cm length, respectively. The simulations are done with a multi-zone 1-D two temperature radiation MHD model self-consistently coupled to a driving circuit. The results show that both time dependence and two temperatures affect the implosion dynamics and the magnitude of the K-shell yields but that the total yield remains unaffected for the most part. For a 3 cm radius load the shell is more efficient at converting kinetic energy to K-shell radiation than a uniform fill at the same radius. The 5 and 7 cm uniform fills are stable and good K-shell radiators. Unfortunately, the two temperature time dependent simulated yields above 10 keV are found to be significantly less than the one temperature and equilibrium simulations.

A series of aluminum wire array implosions with nearly equal line density have been performed on the DOUBLE EAGLE pulse power generator. The measured implosion times, minimum radii, total radiative yields, K-shell yields, and K-shell pulse widths are compared against radiation-hydromagnetic simulations. The simulations treat the plasma as a uniform shell of finite thickness and include a circuit model for the generator. A short circuit and an enhanced resistivity are added to the simulation models in order to improve the agreement with experimental data. In general the final results are encouraging, but indicate that the present state of simulations is short of providing an accurate predictive capability.

In a series of experiments Formvar-supported circular silver-dot targets were simultaneously irradiated with 1.06-\ensuremath{\mu}m and 0.35-\ensuremath{\mu}m laser light in the mid-${10}^{14}$-W ${\mathrm{cm}}^{\mathrm{\ensuremath{-}}2}$ range. In some of the shots, only 0.35-\ensuremath{\mu}m light was used. The 3000-A\r{} thickness of the silver was chosen to assure an electron density in excess of the critical ${10}^{21}$ ${\mathrm{cm}}^{\mathrm{\ensuremath{-}}3}$ at the time of superposition of the 1.06-\ensuremath{\mu}m beam, thereby facilitating the generation of suprathermal electrons by resonance absorption. Both high-resolution and broadband spectral data reveal that higher states of excitation and ionization of neonlike and fluorinelike silver were achieved in the presence of the 1.06-\ensuremath{\mu}m beam. Evidence that this enhanced excitation and ionization is due to suprathermal-electron pumping is provided by the broadband-continuum data which show little or no increase in the thermal-electron temperature, when the 1.06-\ensuremath{\mu}m light is superimposed. Analysis of the data indicates that, in a similarly structured linear target, the gain of the 3p-3s J=2 to 1 neonlike line at 99.6 A\r{} would increase from 0.4 to \ensuremath{\sim}1 ${\mathrm{cm}}^{\mathrm{\ensuremath{-}}1}$ when using both laser wavelengths. This conclusion is independent of the mechanism producing the increased excitation and ionization.

Resonant phOtopumping is an attractive and potentially very efficient technique for achieving x-ray lasing in plasmas. At the Naval Research Laboratory we are pursuing the realization of one of the most promising photopumped schemes wherein heliumlike sodium pumps heliumlike neon. The theoretical side of this research has revealed the conditions required for the sodium and neon plasmas to maximize the possibility of photopumped fluorescence and lasing. On the experimental side, a powerful (25 GW) z-pinch source of sodium line pumping radiation has been developed and characterized. A separate neon plasma, driven by part of the return current from the sodium-bearing plasma, has been deployed side-by-side with respect to the sodium line source at a distance of 5 cm. The presence of photopumping has been indicated in fluorescing spectra. The remaining steps toward achievement of an x-ray laser are reducing the spatial separation of the pumped and pumping plasmas and increasing the pump line power of the pumping, sodium-bearing plasma.

Using axially resolved spectra, we have derived temperature and density profiles of sodium-bearing Z-pinch plasmas produced on the Naval Research Laboratory's Gamble-II generator. The variations in the output power of the Na X 1s/sup 2/ /sup 1/S/sub 0/--1s2p /sup 1/P/sub 1/ line which can be used to pump a Ne IX x-ray laser, are analyzed as functions of mass loading, temperature, and density. The fractional conversion of plasma energy to lasing lines is projected as 10/sup -3/ if an optimum neon lasant plasma can be prepared and pumped to saturation. This would require an increase in load current of less than or equal to 50% from the present 1.2 MA.