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  • 1
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 89 (2001), S. 4719-4726 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Vacuum ultraviolet emission and electrical characteristics of a simple discharge configuration consisting of two planar cylindrical electrodes operated with a dc voltage have been measured over a wide range of He/Xe mixtures and discharge pressures. Breakdown characteristics are consistent with those found in the literature, however current–voltage characteristics and the inferred discharge resistivity suggest the presence of a complex process controlling electron emission at the cathode. Ultraviolet vacuum emission maps of atomic and molecular xenon at 147, 150, and 173 nm, respectively, have been measured as a function of pressure, from 60 to 500 Torr, and gas mixture, from pure Xe to 5% Xe in He. The calibrated ratios of each emission map help to visualize the zones of strongest ultraviolet emission over a wide range of operating conditions. One-dimensional simulations of the breakdown voltage and current discharge have been performed using the commercially available discharge-modeling package SIGLO. Good agreement with experimental results is found in the case of pure helium and xenon, however, in the case of pure xenon, the gas temperature was adjusted (elevated) in order to reproduce the measured current–voltage characteristics. Modeling of the electron number density distribution indicates that the discharge is principally composed of a thick ion sheath near the cathode. © 2001 American Institute of Physics.
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 5 (1998), S. 4488-4497 
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The structure of an expanding low-power hydrogen arcjet plasma is investigated through probe-based measurements of impact pressure and mass flux. Comparisons are made to direct simulation Monte Carlo models (DSMC) of the nonignited flow (cold flow) and continuum magnetohydrodynamic (MHD) models of the arc-heated flow. While general agreement with previous spectroscopic data and DSMC calculations are obtained, the cold flow impact pressures are shown to exhibit features that may be due to probe–flow interactions and rarefied gas effects. The ability to identify shocks in the plume, predicted by the DSMC model and previously observed by Raman spectroscopy, shows that the cold flow probes were capable of resolving major flow features. The impact pressure measurements of arc-heated flow also agree quite well with the results calculated from the MHD model, and it is demonstrated that integrated thrust densities derived from impact pressure measurements are in agreement with direct measurements of thrust using an inverted pendulum thrust stand. Cold flow mass flux measurements appear to agree well with the DSMC model in the core portion of the flow. Using velocity and temperature data obtained from previous laser-induced fluorescence measurements; density, pressure, and thrust profiles were derived from the measured mass flux profiles. The density profile indicates that the dissociation fraction at the exit plane was within the uncertainty of the only direct spectroscopic molecular hydrogen density measurements available in the literature. © 1998 American Institute of Physics.
    Type of Medium: Electronic Resource
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  • 3
    Electronic Resource
    Electronic Resource
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 76 (2000), S. 544-546 
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Vacuum emission, breakdown, and current–voltage characteristics of a large surface area-to-volume ratio planar dc microdischarge have been measured for different He–Xe mixtures in the range of 10%–100% Xe and pressures in the range of 60–500 Torr. The electrical measurements show that the Paschen breakdown curves and the current–voltage characteristics are primarily controlled by the xenon concentration in the mixture. A study of the vacuum ultraviolet emission of xenon atoms at 147 nm and of xenon dimers at 150 nm normalized to the discharge power reveals the presence of local maxima in the emitted intensity as a function of discharge pressure and xenon concentration, indicative of complex excited-state atomic and excimer kinetic processes. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
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  • 4
    Electronic Resource
    Electronic Resource
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 70 (1997), S. 1052-1054 
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We report on the measurement of methyl radical (CH3) densities in a low-density supersonic arcjet plasma used in the synthesis of diamond films. Single-pass, high-sensitivity ultraviolet (UV) absorption spectroscopy has been employed to study the X(2A2″)→B(2A1′) transition of the methyl radical near 216 nm. The minimum detectable CH3 density is found to be ∼4×1013 cm−3, which corresponds to a fractional absorption of 2×10−3 at a gas temperature of 1200 K. The dependence of the measured methyl column density on pressure and CH4/H2 flow ratio has been studied. The results are used to revise our previous estimates of the reactive "sticking" coefficient for CH3, and we now find that it is of order 10−2 under conditions where we have previously documented the growth of high quality diamond films. © 1997 American Institute of Physics.
    Type of Medium: Electronic Resource
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