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From the width of the 656.3-nm Balmer [alpha] line emitted from inductively and capacitively coupled radio frequency (RF), microwave, and glow-discharge plasmas, it was found that inductively coupled RF helium-hydrogen and argon-hydrogen plasmas showed extraordinary broadening corresponding to an average hydrogen atom energy of 250-310 and 180-230 eV, respectively, compared to 30-40 and 50-60 eV, respectively, for the corresponding capacitively coupled plasmas. Microwave helium-hydrogen and argon-hydrogen plasmas showed significant broadening corresponding to an average hydrogen atom energy of 180-210 and 110-130 eV, respectively. The corresponding results from the glow-discharge plasmas were 33-38 and 30-35 eV, respectively, compared to [approximately equal to] 4 eV for plasmas of pure hydrogen, neon-hydrogen, and xenon-hydrogen maintained in any of the sources. Similarly, the average electron temperatures [T.sub.e] for helium-hydrogen and argon-hydrogen inductively coupled RF and microwave plasmas were high (43 200 [+ or -] 5% K, 18 600 [+ or -] 5% K, 30 500 [+ or -] 5% K, and 13 700 [+ or -] 5% K, respectively); compared to 9300 [+ or -] 5% K, 7300 [+ or -] 5% K, 8000 [+ or -] 5% K, and 6700 [+ or -] 5% K for the corresponding plasmas of xenon-hydrogen and hydrogen alone, respectively. Stark broadening or acceleration of charged species due to high electric fields cannot explain the inductively coupled RF and microwave results since the electron density was low and no high field was present. Rather, a resonant energy transfer mechanism is proposed. Index Terms--Electron temperature, glow-discharge plasma, microwave plasma, resonant energy transfer mechanism, radio frequency (RF) plasma, significant line broadening.

Each of the ionization of [Rb.sup.+] and cesium and an electron transfer between two [K.sup.+] ions ([K.sup.+]/[K.sup.+]) provide a reaction with a net enthalpy of an integer multiple of the potential energy of atomic hydrogen, 27.2 eV. The corresponding Group I nitrates provide these reactants as volatilized ions directly or as atoms by undergoing decomposition or reduction to the corresponding metal. The presence of each of the reactants identified as providing an enthalpy of reaction of an integer of that of the potential energy of atomic hydrogen (m * 27.2 eV) formed a low applied temperature, extremely low-voltage plasma called a resonance transfer (RT)-plasma having strong vacuum ultraviolet (VUV) emission. In contrast, magnesium and aluminum atoms or ions do not ionize at integer multiples of the potential energy of atomic hydrogen. Mg[(N[O.sub.3]).sub.2] or Al[(N[O.sub.3]).sub.3] did not form a plasma and caused no emission. For further characterization, we recorded the width of the 6563 [Angstrom] Balmer [alpha] on light line on light emitted from RT-plasmas. Significant line broadening of 18, 12, and 12 eV was observed from an RT-plasma of hydrogen with KN[O.sub.3], RbN[O.sub.3], and CsN[O.sub.3], respectively, compared to 3 eV from a hydrogen microwave plasma. These results could not be explained by Stark or thermal broadening or electric field acceleration of charged species since the measured field of the incandescent heater was extremely weak, 1 V/cm, corresponding to a broadening of much less than 1 eV. Rather the source of the excessive line broadening is consistent with that of the observed VUV emission, an energetic reaction caused by a resonance energy transfer between hydrogen atoms and [K.sup.+]/[K.sup.+], [Rb.sup.+] , and cesium, which serve as catalysts. KN[O.sub.3] and RbN[O.sub.3] formed the most intense plasma. Remarkably, a stationary inverted Lyman population was observed in the case of an RT-plasma formed with potassium and rubidium catalysts. These catalytic reactions may pump a continuous wave HI laser as predicted by laser equations and a collisional radiative model used to determine that the observed overpopulation was above threshold. Index Terms--Continuous wave (CW) HI laser, Group I catalysts, hydrogen catalysis, inverted Lyman population.

The generation of electrical energy using direct plasmadynamic conversion (PDC) is studied experimentally for small-scale, chemically-assisted plasmas (CA-plasma) for the first time. Glow discharge and microwave-generated plasma sources are operated at power levels on the order of a few to 50 W in the discharge case and up to 12.83 W/[cm.sup.3] in the microwave case. Extracted power approaching 1/4 W has been achieved as a demonstration. It is envisioned that such a system may be readily scaled to a few hundred Watts to several tens of kilowatts output power for microdistributed commercial applications (e.g., household, automotive, light industry, and space based power). Three-quarter inch long by 0.040-in diameter cylindrical PDC electrodes have been tested in a 10-50 W direct current, glow discharge plasma device with He or Ar as the working gas at 0.3-3.0 torr. The PDC anode was magnetized in the range of 0-700 G with a 1.5-in water cooled Helmholtz electromagnet. Open circuit voltages up to 6.5 V were obtained across the PDC electrodes at 1 torr He and 350-G field. The collector voltage was shown to be a function of applied magnetic field strength B and peaking at about 300 G. A variety of resistive loads were connected across the PDC electrodes, extracting continuous electrical power up to 0.44 mW. The power/load curve peaks at 0.44 mW for a 20 k[OMEGA] load indicating the impedance matching condition with the plasma source. The most severe limitation to collector output performance is shown to be plasma conductivity. Collector power drops sharply with increasing neutral gas fill pressure in the glow discharge chamber at constant discharge current indicating that electron collisions with neutral gas atoms are responsible for the reduction in conductivity. Scale-up to higher power has been achieved with the use of a microwave plasma generator. A 0.75-in long by 0.094-in diameter PDC anode was magnetized to ~140 G resulting in open circuit PDC voltages in excess of 11.5 V for He plasmas at ~0.75-1 torr and 50 sccm flow. Due to higher conductivity, load matching was now obtained at ~600 [OMEGA]. Langmuir probe results indicate good agreement between the conductivity change and the electron to neutral density ratio scale-up. For this source and electrode configuration, PDC power as high as ~200 mW was demonstrated in He at 0.75 torr for a microwave input power density of ~8.55 W/[cm.sup.3]. Considering an electron mean-free path as the scale for collector probe influence in the plasma, the peak extracted power density is ~1.61 W/[cm.sup.3], corresponding to a volumetric conversion efficiency of ~18.8%. Index Terms--Microwave plasma, plasmadynamic, power conversion.

The generation of electricity using direct electrostatic and magnetohydrodynamic (MHD) conversion of the plasma-particle energy of small to midsize chemically assisted microwave or glow discharge plasma (CA-plasma) power sources in the range of a few hundred Watts to several tens of kilowatts for microdistributed commercial applications (e.g., household, automotive, light industry, and space-based power) is studied for the first time. In the determination of the effect of plasma parameters on conversion efficiency, careful attention was paid to the unique plasma conditions of low-pressure, low-ionization fraction, and nonthermal ion energies that are much greater than that of the thermal ions of traditional MHD but much lower than those of a fully ionized plasma typically generated for fusion experiments. The density of plasma ions and neutrals and their cross sections for processes such as charge exchange were also considered. The most important parameters were found to be charged-particle density and energy, as well as the large inventory of neutral gas atoms and molecules. Momentum and charge exchange of plasma ions with the large background fraction of neutrals represents limitation to conversion efficiency. Two conversion technologies were examined in some detail. We considered the possibility of converting a CA-plasma using adaptations of a member of the broad category of electromagnetic direct converters previously developed for recovery and conversion of the high energy particles lost from tandem mirror and magnetically confined plasmas, and an MHD converter previously developed for conversion of high pressure combustion gases to electricity. While it was found that both conversion techniques performed well under ideal conditions for conversion of plasma to electricity showing conversion efficiencies of >50%, the tight coupling of plasma cell and converter, size limitations, particle energy, and the substantial inventory of relatively low energy neutrals may substantially reduce the efficacy of direct electrostatic converters under these conditions. However, MHD conversion of CA-plasmas appears feasible at ~50% efficiency with a simple compact design. Index Terms--Direct energy conversion, magnetohydrodynamics, power sources.

This paper summarizes preliminary experimental and theoretical research that was directed toward the study of quasi-steady-state power flow in a large, unoptimized, multimegawatt coaxial plasma thruster. The paper addresses large coaxial thruster operation and includes evaluation and interpretation of the experimental results with a view to the development of efficient, steady-state, megawatt-class magnetoplasmadynamic (MPD) thrusters. Experimental studies utilized the Coaxial Thruster Experiment (CTX) facility at the Los Alamos National Laboratory. The unoptimized thruster, 1 m in length with inner and outer tungsten-coated electrode diameters of 0.37 and 0.56 m, respectively, was operated over a range of peak power levels (nominally 10-40 MW) in order to ascertain high-power performance scaling. In addition to pure self-field operation, an unoptimized applied magnetic field configuration, with adjustable flux densities, was used to form a rudimentary, annular magnetic nozzle. In this initial research, an accurate power balance was precluded due to the lack of spatial resolution of power deposition on the electrodes. However, the data, together with a calorimetric IR data reduction algorithm, did quantify energy flux deposition on electrode surfaces and provided a qualitative picture of global power flow and thruster performance. Highlights of this study include the observations that the measured longitudinal flow velocity of the propellant was in essential agreement with the prediction of self-field nozzle theory, achieving Alfvenic flow velocities of approximately equal to 10 to the fifth power m/s. Furthermore, radiative emission was a negligible power loss mechanism (