The generation of liquid fuels like methanol (MeOH) and dimethyl ether (DME) from the greenhouse gases (GHG) methane and carbon dioxide has recently attracted growing attention. Investigations of this kind are part of efforts to reduce GHG emissions to the atmosphere. For our investigations we used a tubular dielectric barrier discharge reactor with an annular discharge gap of 1 mm width and a cylindrical quartz dielectric of 2.5 mm thickness. It was operated in methane-oxygen mixtures at pressures between 1 and 4 bar. The discharge was operated at a frequency of about 18 kHz. The power density could be raised up to 20 kW/m^2 of electrode area by increasing the applied voltage. Up to 1.3% MeOH and .4% DME were measured after a single passage through a discharge gap of 310 mm length by GC and GC/MS detection. These values were obtained at 2 bar, substantially lower values were measured at 1 or 4 bar operating pressure. At high specific energies >8 eV per molecule of feed gas the MeOH concentration decreased and methyl formate appeared in the product stream.
[H3A.02] Hollow Electrode Discharge Triodes
K.H. Schoenbach, F.E. Peterkin, T. Tessnow (Physical Electronics Research Institute, Old Dominion University, Norfolk, VA), W.C Nunnally
The current through a direct current micro-hollow electrode (electrode hole
diameter: 0.7 mm) discharge in argon was shown to be controllable by means
of a third, external electrode placed close to the cathode opening. By
increasing the potential of the positively biased control electrode from
zero to 30 V the discharge current could be linearly reduced from 5 \muA
to 0.75 \muA, at a discharge voltage of 300 V. The current-voltage
characteristic of the micro-hollow electrode discharge was found to have a
positive slope, allowing parallel discharge operation without ballast. By
drilling holes through a metal-plated, dielectric film, an array of hollow
electrode discharges could be generated. It was shown that each discharge
responds individually to variations in the potential of the corresponding
external control electrode. The simplicity of the electrode configuration
and the possibility of linear, electrical control of the individual
discharge currents offers the possibility to use these triode arrays in
addressable flat panel displays (patent pending).
[H3A.03] Hydrogen fractional dissociation in H_2/He mixture discharges
B.N. Ganguly, P. Bletzinger, R. Nagpal (Wright Laboratory, WPAFB, OH)
The fractional dissociation efficiency of H_2 in He-H_2 and H_2-N_2-He gas mixture discharges has been measured by two-photon laser induced fluorescence in the downstream region of a helical resonator plasma source operating in the inductive mode. The measurements were performed with 0.5 Torr up to 3 Torr total gas pressure, and 40-60 Watt input power. For lower pressure discharge conditions where 50-60% of total input power goes to H_2 dissociation, the increasing He dilution leads to a decrease in H atom density nearly proportional to the H_2 partial pressure. For higher pressure discharges the fractional H_2 dissociation efficiency increased with increase in He dilution. The measurements are consistent with the calculated direct electron impact dissociation rates of H_2 for He-H_2 gas mixture discharges operating from 30-120 Td. This is in contrast to H_2-N_2-He gas mixture discharges, where heavy particle energy transfer processes from the N_2 vibronic states have to be invoked to explain the observed dissociation efficiency.
[H3A.04] Measurements of N_2(A) Metastable State Density in a Nitrogen Glow Discharge
J.Sebastian Oddone, Juan A. Curial, Tony J. Coschignano, Kenneth A. Hardy, J.W. Sheldon (Physics Department, Florida International University)
Measurements of the rate of effusion of metastable N_2(A) molecules from a slit in the anode of a low pressure, low voltage, hot cathode discharge are reported. The effusing metastables are collimated into a beam from which charged particles are electrostatically removed. The beam is chopped near the anode source and detected by counting pulses initiated by metastable ejection of Auger electrons in a channeltron. This arrangement allows time-of-flight (TOF) analysis of the beam. The metastable yield as a function of discharge pressure, temperature, current, voltage and axial magnetic field are reported. The temperature is determined by fitting the TOF spectra to the function expected from a Maxwellian distribution of N_2(A) in the discharge. The yield is compared with a kinetic model of N_2(A) production following the work of Cernogora et al. (G. Cernogora, L. Hochard, M. Touisau and C. Matos Ferreira, J. Phys. B. At. Mol. Phys. 14, 2977 (1981).) (Supported by grants from NASA (NAG 5-2583) and the AFSOR(F49620-93-1-015DEF).)
[H3A.05] Optical Pumping of a He RF Discharge
M.A. Humphrey (Western Michigan University), B.G. Birdsey (University of Nebraska-Lincoln), K.W. Trantham (The Australian National University, Canberra, Australia), H. Batelaan, T.J. Gay (University of Nebraska-Lincoln)
A helium RF discharge has been investigated as a source of polarized electrons. By optical pumping with distributed Bragg reflector (DBR) diode lasers, metastable 2^3S_1 He atoms have been spin oriented, and a measure of the metastable polarization has been made. Since the predominant ionization channels in the discharge favor production of spin-polarized electrons from the metastable atoms, a beam of polarized electrons can be extracted. (M. V. McCusker, P.R.A. 5, 177 (1972)) In previous measurements with a DC discharge, we have measured between 6% and 7% electron polarization in an extracted current of 200 microamps. (R. J. VanDiver, Ph.D. Thesis, Univ. of Missouri-Rolla (1994, unpublished)) We will present results on the polarization of the He atoms as a function of various discharge and pump laser parameters. This work is supported by NSF grant PHY-9504350.