Graydon K. Anderson

Impulse coupling to targets in vacuum by KrF, HF, and CO2 single‐pulse lasers

We present a laser‐target scaling model which permits approximate prediction of the dependence of ablation pressure, mechanical coupling coefficient, and related parameters in vacuum upon single‐pulse laser intensity (I), wavelength (λ), and pulse width (τ) over extremely broad ranges. We show that existing data for vacuum mechanical coupling coefficient for metallic and endothermic nonmetallic, surface‐absorbing planar targets follows this empirical trend to within a factor of 2 over 7 orders of magnitude in the product (Iλ(τ)1/2). The comparison we present is valid for intensity equal to or greater than the peak‐coupling intensity Imax, where denseplasma formation mediates laser‐target coupling. Mechanical coupling coefficients studied ranged over two orders of magnitude. The data supporting this trend represent intensities from 3 MW/cm2 to 70 TW/cm2, pulse widths from 1.5 ms to 500 ps, wavelengths from 10.6 μm to 248 nm, and pulse energies from 100 mJ to 10 kJ. With few exceptions, data approximating o...

Plasma remediation of trichloroethylene in silent discharge plasmas

Plasma destruction of toxins, and volatile organic compounds in particular, from gas streams is receiving increased attention as an energy efficient means to remediate those compounds. In this regard, remediation of trichloroethylene (TCE) in silent discharge plasmas has been experimentally and theoretically investigated. We found that TCE can be removed from Ar/O2 gas streams at atmospheric pressure with an energy efficiency of 15–20 ppm/(mJ/cm3), or 2–3 kW h kg−1. The majority of the Cl from TCE is converted to HCl, Cl2, and COCl2, which can be removed from the gas stream by a water bubbler. The destruction efficiency of TCE is smaller in humid mixtures compared to dry mixtures due to interception of reactive intermediates by OH radicals.

Effect of air and oxygen content on the dielectric barrier discharge decomposition of chlorobenzene

Experiments were performed on the plasma-assisted decomposition of dilute concentrations of chlorobenzene in air/oxygen and argon/oxygen gas mixtures at atmospheric pressure using a coaxial geometry single dielectric barrier discharge for different oxygen concentrations and energy densities. The results show that the decomposition process requires higher energy densities using air mixtures compared to argon/oxygen mixtures and is not linearly dependent on the oxygen content for a given energy density. The main decomposition products detected in the offgas were carbon dioxide and carbon monoxide.

Effect of Plasma Chemistry on Activated Propane/Air Flames

We have developed a dielectric-barrier-discharge propane burner where propane is activated prior to being mixed with air and burned. In contrast to most work reported by others, combustion in our apparatus occurs away from the plasma region, thereby greatly reducing electric field effects, thus providing more insight into the role played by plasma chemistry. Flame flashback images were recorded as a function of the separation between the propane plasma and injected air, and the mixing length of the activated propane/air mixture. The lifetime of activated propane was found to be about 150 ms, while the lifetime of an activated propane/air mixture was measured to be about 300 ms. Using a gas-chromatograph diagnostic, H2, CH4, C2 H2, C2H4, and C2H6 were identified as the principal propane-discharge fragments, however, these are not the dominant species causing flame flashback behavior. The presence of reactive radical species is suggested to be a main factor governing flame flashback

Decomposition of Ethane in Atmospheric-Pressure Dielectric-Barrier Discharges: Experiments

It is well known that electric fields can influence combustion processes. When the magnitude of an external applied electric field exceeds the breakdown field of the fuel gas or fuel/oxidizer mixture, plasma effects dominate. The earlier work in the field of plasma-assisted combustion has demonstrated that dielectric-barrier-discharge (DBD)-driven nonthermal plasmas (NTPs) can increase flame speed and extend the combustion of hydrocarbon fuel gases into very lean-burn regimes. In this paper, results on the decomposition of ethane (C2H6) by DBDs at atmospheric pressure will be presented. The authors have chosen ethane for this paper because its gaseous electronics properties (electron-impact dissociation cross sections, drift velocity) are available in the literature. A subsequent paper will present results on the calculated yield of DBD-driven plasma decomposition products of ethane, as predicted by plasma-chemistry modeling. In this paper, results on experiments carried out to determine the decomposition products of ethane, as measured by gas chromatography are presented. An atmospheric-pressure DBD reactor processed a flowing gas stream of chemically pure ethane in the regime of plasma specific energy ranging from 1200 to 2400 J/std lit. The major stable decomposition products were H2, CH4, C2H2, and C2H4. These results are important in assessing the possibility of using NTPs to enhance the combustion of hydrocarbons

Hydrogasification of Carbon in an Atmospheric Pressure Microwave Plasma

Hydrogasification of carbon (C + 2H₂ rarr CH₄) was studied using a microwave plasma in atmospheric pressure Ar/H₂ mixtures. When the activated Ar/H₂ gas stream interacted with cold carbon particles downstream of the microwave cavity, CH₄ (methane) was the only stable gasification product, as measured by gas chromatography. However, when carbon particles were injected into the plasma within the microwave cavity, both C₂H₂ (acetylene) and C₂H₄ (ethylene) were measured in addition to CH₄. To identify a gasification mechanism by the microwave plasma, UV emission and minimum operational power required to maintain plasma were measured. From the experimental results, the initial reaction step leading to CH₄ is thought to be a chemisorption-desorption reaction of hydrogen radical onto a carbon particle. For the C₂H₂ and C₂H₄ generation, hydrogen ion reaction with a carbon particle is suggested.

Infrared Spectroscopy of TeF6

Abstract Fourier transform and grating IR spectrometers and tunable diode lasers have been used to record the IR spectrum of TeF 6 . The isotopic structure in the stretching fundamental ν 3 is resolved, revealing a tellurium isotope shift of approximately 0.68 cm −1 amu −1 . Some of the rotational structure in the P and R branches of ν 3 of 99.3% 130 TeF 6 is also resolved and analyzed to yield a Coriolis constant ζ 3 = 0.225. Integrated absorptivities are reported for ν 3 and for the stronger combination bands. The isotope shifts and Coriolis constants are used to fix the general quadratic symmetry and valence force fields, and the force constants of the Group VI series SF 6 , SeF 6 , and TeF 6 are compared and discussed.

Electrical Conductances of Aqueous Solutions of Inorganic Nitrates at 25-505 C and 100-490 Bar

Abstract A simple Pt electrode was used to determine the electrical conductances of 0.00393, 0.00992 and 0.0379 m NaNO3 and 0.00911 m LiNO3, 0.00910 m CsNO3 and 0.00946 m Ca(NO3)2 solutions. Temperatures ranged from 25 to 505°C at pressures ranging from 100 to 490 bar. The electrode was calibrated against the conductance of 0.010 m hydrothermal NaCl solutions. Preliminary limiting equivalent conductances and dissociation constants were obtained for hydrothermal NaNO3 solutions. The alkali nitrate series behaved similarly to the alkali chloride series: the electrical conductance decreases with decreasing cation radius. This seemingly paradoxical result is due to the stronger electric field and hence the greater tendency for ion pairing and larger solvation spheres associated with smaller cations. Nearly complete ion association is observed at low-density supercritical conditions. Maximum conductances were obtained at about 300°C and densities increasing from about 500 kg m−3 to 725 kg m−3 with increasing concentration. Limiting conductances and pKa values for NaNO3 solutions were similar to those for NaCl solutions, with NaNO3 being the weaker electrolyte. Ca(NO3)2 conductances follow similar trends to K2SO4. The data suggests that nearly complete dissociation occurs below 200°C, but that appreciable association to form monovalent cations occurs at higher temperatures.

Non-Thermal Plasma-Assisted Combustion Research at Los Alamos

This study investigates the use of nonequilibrium silent electrical discharge plasmas to combustion processes, particularly for enhancing combustion stability, efficiency, and reducing undesirable emissions. Dielectric barrier discharge (DBD) experiments are carried out with gaseous hydrocarbon fuels (methane, ethane, propane and butane) as well as the gasoline surrogate liquid iso-octane. DBDs allow free radicals to act in propagating combustion reactions, as well as to produce intermediate species in fragmenting hydrocarbons.