Thesis (M.S.)--University of Michigan, 1966.

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An atmospheric pressure argon glow discharge is shown to detect trace levels of carbohydrates in aqueous flowing systems, using either of two glow discharge solution interface configurations. The first configuration consists of an oscillating glow discharge sustained between a flowing aqueous cathode and platinum anode. Picomole and micromolar mass and concentration detection limits, respectively, are obtained for sucrose in an aqueous flow injection system when monitoring discharge oscillation frequency or discharge current. The second configuration consists of a non-oscillating glow discharge sustained between metallic electrodes near the flowing output of a high performance liquid chromatography system. A conductivity detector detects the acidic product formed when each carbohydrate elutes and is exposed to the glow discharge. This detector yields femtomole and nanomolar mass and concentration detection limits, respectively, for a variety of carbohydrates and competes with the best of the commercially available liquid chromatography carbohydrate detectors. An increase in the discharge electrode spacing or reduction in the liquid flow rate increases detector sensitivity, since the discharge area and solution exposure time are increased, respectively. The aqueous carbohydrate products formed from exposure to the glow discharge are similar to those formed from exposure to high energy radiation. Acid, hydrogen peroxide, and an absorbing species all form in amounts proportional to carbohydrate concentration and glow discharge exposure time, with yields approximating those encountered when using high energy radiation. / Graduation date: 1997

Three aspects of glow discharges have been studied: glow discharge oscillations, sputtering, and coupling between cathode and anode regions the two most important regions in a glow discharge. Cathode and anode processes are tightly coupled by electron and ion coupling effects. Both electron and ion coupling effects were observed by studying excited Ar atoms in the cathode and anode regions and observing laser-induced space charge variations and the optogalvanic effect. Laser-induced space charge variations in the glow discharge were observed by the change in potential of an electrical probe. This signal, called the optopotential signal, provides useful information about the cathode and anode processes, and may become another useful spectroscopic detection method. Glow discharge oscillations are old phenomena but our mechanistic understanding of the processes involved continues to grow. A mechanism study is important especially now since a new type of sensitive GC detector is being developed based on this phenomenon. A SPAN model of glow discharge oscillation is proposed: source formation, propagation, accumulation, and neutralization of space charges. Electrode coupling couples the neutralization and source formation processes thus completing the feedback loop necessary for some of the observed oscillations to occur. Four modes of oscillations were found. Emission, space potential and current monitoring, and forced oscillations were used to monitor and identify the mechanisms. Studies of cathodic sputtering with gas flow rates up to 2.13 L/min/jet were carried out in an Atomsource sputtering atomizer with Ar as the jet gas and Cu as the cathode sample. These flow rates are 20-fold greater than those normally used and were found to increase net sputtering yield significantly. A fourfold increase in net sputtering yield was observed when the number of jets in use was decreased from six to one, with the gas flow rate and other conditions held constant. Possible explanations for these effects are offered. / Graduation date: 1996

A direct-current, non-equilibrium surface glow discharge plasma in the presence of a Mach 2.85 flow is studied experimentally for flow control applications. The discharge is generated with pin-like electrodes flush mounted on a ceramic plate with sustaining currents from 25 mA to 300 mA. In the presence of a supersonic flow, two distinct discharge modes - diffuse and constricted - are observed depending on the flow and discharge operating conditions. In cathode upstream location, both diffuse and constricted discharges are observed while in cathode downstream location, the discharge mostly exhibits either constricted mode or bistable mixed mode. The effect of the discharge on the flow ("plasma actuation") is characterized by the appearance of a weak shock wave in the vicinity of the discharge. The shock is observed at low powers (~10 W) for the diffuse discharge mode but is absent for the higher power (~100 W) constricted mode. High speed laser schlieren imaging suggests that the diffuse mode plasma actuation is rapid as it occurs on a time scale that is less than 100 [mu]sec. Rotational (gas) and vibrational temperatures within the discharge are estimated by emission spectral line fits of N₂ and N⁺₂ rovibronic bands near 365-395 nm. The electronic temperatures are estimated by using the Boltzmann plot method for Fe(I) atomic lines. Rotational temperatures are found to be high (~1500 K) in the absence of a flow but drop sharply (~500 K) in the presence of a supersonic flow for both the diffuse and constricted discharge modes. The vibrational and electronic temperatures are measured to be about 3000 K and 1.25 eV (14500 K), respectively, and these temperatures are the same with and without flow. The gas (rotational) temperature spatial profiles above the cathode surface are found to be similar for the diffuse and constricted modes indicating that dilatational effects due to gas heating are similar. However, complete absence of flow actuation for the constricted mode suggests that electrostatic forces may also play an important role in supersonic plasma-flow actuation phenomena. Analytical estimates using cathode sheath theory indicates that ion pressure within the cathode sheath can be significant resulting in gas compression in the sheath and a corresponding expansion above it. The expansion in turn may fully negate the dilatational effect in the constricted case resulting in an apparent absence of forcing in the constricted case. Plasma-induced flow velocity reaches about 1 m/s in stagnant air at the discharge current of order tens of milliamps. This electrostatic forcing in the direction from anode to cathode can play an important role in the boundary layer of supersonic flow. / text

Thesis (Ph. D.)--West Virginia University, 2009. / Title from document title page. Document formatted into pages; contains xxvi, 176 p. : ill. (some col.). Includes abstract. Includes bibliographical references (p. 93-98).

Thesis (Ph. D.)--University of Texas at Austin, 2007. / Vita. Includes bibliographical references.

Spectroscopic investigations have been carried out on hollow cathode discharges adapted from laser technology for use as a spectroscopic light source and the argon inductively coupled plasma (ICP) as an excitation source for nonmetal emission. High and low voltage aluminum and copper hollow cathode discharges were studied as a source of ionic and resonant atomic metal emission. The high voltage versions achieve strongly positive current-voltage behavior through utilization of the obstructed discharge phenomenon. The current-pressure-intensity-voltage relationships for low and high voltage copper hollow cathode discharges were studied with the inert gases He, Ne, Ar, Kr, and Xe. The intensity for copper resonant atomic emission with the fill gases Ar, Kr, and Xe improved relative to neon in the high voltage lamp when compared to the low voltage lamp. Absorption measurements through the cathode bore show the ground state atom density to increase with the atomic weight of the fill gas at any given level of intensity, at the fill gas pressure yielding highest resonant atomic copper emission. The estimated ion/atom intensity ratio is increased with fill gases which have metastable or ionization energies greater than the excitation energy of the ion transition. A copper hollow cathode lamp incorporating a short positive column discharge in front of the cathode opening was investigated for its lineshape as measured spectroscopically and by its atomic absorption sensitivity. Incorporation of this positive column allowed higher intensities to be obtained at the same line quality as a commercial hollow cathode lamp. An enlarged cathode volume also improves the lineshape at a given intensity. Inductively coupled plasma spectra for the elements C, O, N, Cl, P, S, and Br were obtained in the vacuum ultraviolet utilizing a vacuum polychromator and SWR film. The detection limit for injected O₂ and N₂ detected electronically by the VUV emissions is 1.3 and 0.9 micrograms respectively with this system. A VUV filter photometer was utilized for oxygen and phosphorus analysis. The detection limit for injected oxygen was 1 microgram with this photometer; the detection limit for phosphorus as inorganic phosphate in aqueous solution is 10⁻³ M. The bandpass of the photometer limits its selectivity.

Thesis (Ph. D.)--West Virginia University, 2002. / Title from document title page. Document formatted into pages; contains xvii, 252 p. : ill. (some col.). Vita. Includes abstract. Includes bibliographical references.

Thesis (M.S.)--University of Michigan, 1966.