In the process under development, coal suspended in mixtures of CH4, H2, and steam is rapidly heated to temperatures above 1,400°C under 5–7 MPa for at least 1 s. The coal first decomposes into volatiles and char while CH4 is converted into CO/H2 mixtures. Then the char is converted into CO/H2 mixtures via steam gasification on longer time scales, and into CH4 via hydrogasification. Throughout all stages, homogeneous chemistry reforms all intermediate fuel components into the syngas feedstock for methanol synthesis. Fully validated reaction mechanisms for each chemical process were used to quantitatively interpret a co-gasification test series in SRI’s lab-scale gasification facility. Homogeneous reforming chemistry generates equilibrium gas compositions at 1,500°C in the available transit time of 1.4 s, but not at any of the lower temperatures. Methane conversion in the gas phase increases for progressively hotter temperatures, in accord with the data. But the strong predicted dependence on steam concentration was not evident in the measured CH4 conversions, even when steam concentration was the subject test variable. Char hydrogasification adds CH4 to the product gas stream, but this process probably converts no more than 15–20

This paper reports detailed product distributions for the devolatilization of five coals during transient heating at a rate of 7000 K/s and a pressure of 1.0 MPa. Major noncondensable gases were resolved into C-1-C-4 hydrocarbons, oils, CO, CO2, H-2, and H2O. Fuel-N release was monitored in terms of the tar-N and char-N contents. Elemental compositions are reported for the tars and chars. All major products were monitored in individual tests; therefore, closures on the balances on total mass, carbon, hydrogen, and nitrogen clearly indicate the quality of these data sets. All the measurements were resolved in fine time increments from the onset of primary devolatilization through the attainment of ultimate yields. The novel heating configuration in the tests essentially eliminated secondary volatiles pyrolysis chemistry, so the product distributions are especially well-suited to validating the proposed devolatilization mechanisms. FLASHCHAIN, which is one of the network depolymerization models, interprets the most important aspects of the pressure effect on devolatilization for all but one coal, based solely on the proximate and ultimate analyses of the coals and the operating conditions in the tests.

This paper introduces an experimental facility to study coal pyrolysis at 10 atm (1.0 MPa). The system processes a stream of coal entrained in argon gas through an inductively heated furnace at 1850 K. Due to the different absorptive properties of the coal and gas, the coal. is heated to temperatures on the order of 1100 K, while the gas remains relatively cool, quenching the products of primary pyrolysis. The extent of devolatilization is controlled by varying the residence time of the coal within the furnace. in this way, the products of primary coal devolatilization can be resolved in time from the onset of devolatilization to the attainment of ultimate yields. Char and tar yields are measured at each residence time, while major noncondensable gases are resolved into C-1-C-3 hydrocarbons, oils, carbon oxides, water, hydrogen, and nitrogen species. To validate the accuracy of the test method, the complete product distribution from individual runs are analyzed to formulate mass and elemental C/H/N balances. The performance of the test facility is illustrated with test results for a high-volatile bituminous coal.

The reflected-shock-heated gas in a shock tube was used to measure the electronic transition moment, R2e, for the A1π−X1σ+ band system of SiO. The absorption spectra of several different gas mixtures were recorded using an optical multichannel analyzer in the 220–310 nm wavelength range. Synthetic spectra were compared with experimental spectra to determine the R2e as a function of internuclear distance, r. Best agreement was achieved if the theoretical values of Langhoff and Arnold are multiplied by a constant value of 1.3, or if they are shifted by 0.25 Bohr toward larger r. However, both our results and the theoretical values are in disagreement with two recent laser-induced fluorescence determinations. We find a transition moment that decreases with increasing r, having a value R2e = 1.3 ± 0.17 atomic units at the equilibrium internuclear distance of 3.0 Bohr.

Properties of reduced density channels created by energy deposition from electron beams propagating in air are presented. A multi-beam laser deflection technique used to diagnose the channels is described, as are representative examples of density channels formed in multi-pulse propagation experiments performed at the Advanced Test Accelerator at the Lawrence Livermore National Laboratory.

: Microwave interactions with a cold, collisional plasma having gradual density gradients were studied. The plasma was created by the photoionization of tetrakisdimethylaminoethylene (TMAE) vapor seeded into atmospheric pressure helium. Photoionization was provided primarily by sparkboard Spatial scans of the absorption of a microwave probe beam along chords across the plasma, with subsequent Abel inversion, yielded three-dimensional plasma density profiles that showed a gradual decrease in the peak plasma density versus distance away from the sparkboard. When a 58cm-diameter reflector was illuminated with 10-GHz microwaves in an anechoic chamber, the plasma sorbed as much as 28 dB in direct reflection, with similar attenuation of the normally weak side-scattered and cross-polarized radiation.The attenuation was compared with model predictions. Detailed analysis of the temporal and spatial dependence of the electron density following ionization that both recombination and attachment processes influenced the plasma decay. The recombination rate of TMAE was found to be (9.0 +/- 1.1) x 10(-6) cm3 s(-1) for 300 K electrons. This work confirms the effectiveness of a cold, collisional plasma as a broadband, switchable wave absorber.

Experiments and analytical methods for determining electron-ion recombination and attachment coefficients in highly collisional, cylindrically symmetric plasmas are presented. Photoionization by sparkboard light sources of tetrakisdimethylaminoethylene (TMAE) seeded in atmospheric-pressure helium is used to produce the plasma. The electron density is probed by microwave transmission techniques. The effective recombination coefficient for electrons recombining with TMAE ions in atmospheric pressure helium is found to be (9.0±1.1)×10−6 cm3 s−1 for Te=300 K.

Strong microwave absorption was observed when a 10 GHz source illuminated an underdense collisional plasma that had a density gradient scale length several wavelengths long. Significant reductions in angular scattering and cross-polarized components were also observed. These experiments confirm that absorption was the dominant process. The plasma was created by the photoionization of tetrakisdimethylaminoethylene molecules seeded into atmospheric pressure helium. Sparkboard arrays provided the intense vacuum ultraviolet ionizing radiation. Plasma density profiles were measured using transverse scans of 9.7 GHz probe microwaves and were found to approximate an Epstein profile. The absorption at 10 GHz by this plasma was as large as 28 dB in direct backscattering and 15–20 dB when orthogonally polarized microwaves were launched and detected. The peak absorption scales with sparkboard energy in a way that suggests that electron-ion recombination is the dominant electron-loss mechanism at high plasma densities.

We report on experimental measurements of the microwave attenuation in highly collisional plasmas created by the photoionization of tetrakis-dimethylamino-ethylene (TMAE) mixed in atmospheric pressure helium contained in a conical frustum, thin-film-mylar vessel. Separate experiments, examining microwave interactions from two different photoionization sources, were performed. The sources were placed near the bottom baseplate consisting of 60-cm diameter, 360-cm focal length aluminum reflector. Best results for peak microwave attenuation were achieved with a windowless, two-dimensional spark array dissipating total energies as high as 135 Joules in 10 μs. This light source is expected to generate substantial energy in the vacuum ultraviolet (VUV), peaking at 80 nm, thus efficiently ionizing TMAE (ionization potential= 5.4 eV). Lower ionization levels, although lasting for significantly longer durations, were achieved with modified commercial, high-energy flashtubes dissipating as much as 2400 Joules.

Radiative emission in the NO γ-band system occurs when air at a few Torr initial pressure is shock-heated at sufficiently high temperatures of 3500–7000 K. Emission spectra of this system in shocks indicate that collisional quenching of the emitting A2Σ+ state is a critical quantity controlling the intensity. Quenching of excited NO by NO itself has been measured using direct time decay of laser-induced fluorescence in the shock tube at 3500 K. The cross section (2−σ error) is 59±20 Å2, compared to the room temperature value 37±8 Å2. At 3500 K, N2 also quenches NO with a cross section ∼2 Å2, much larger than the value at 300 K.

An extensive series of time-resolved measurements of Xe*2 second continuum emission spectra has been completed to reveal the spectra of the relaxed individual emitting states. Optical pumping of high-pressure Xe by a short-pulse F2 laser at 157.6 nm was used together with a gated optical multichannel analyzer detector or monochromator and boxcar integrator to time resolve the emission bands of the 0+u and 1u states. The bands are broader than expected and have center wavelengths close together. Curve fits to the data yield the parameters for the fully relaxed states: 1u:λc =171.4±0.6 nm, Δλ=12.2±0.2 nm and 0+u: λc =170.4±0.6 nm, Δλ=13.1±0.3. Temperature-dependent measurements from 246 to 413 K show a rapidly broadening band width with temperature. The results provide the first definitive measurement of the individual excimer emissions from the Xe2(0+u) and Xe2(1u) states. From these measurements and the known ground-state potential, we have derived 0+u and 1u potentials that reproduce the emission bands and temperature dependence very well.

The Multiple Pulse Propagation Experiment (MPPE) was designed to determine the hose stability properties of an intense relativistic electron beam in a beam generated density channel and to investigate range extension with increasing pulse number in the burst. This experiment used a 10-MeV electron beam generated by the Advanced Test Accelerator (ATA). The electron beam current was expected to be at least 6-kA with an equilibrium radius of 0.5 cm (RMS) in the gas. This last constraint implied an unnormalized, RMS beam emittance of 20 mrad-cm. In order to achieve beam stability against hose, each electron beam pulse had to be tailored in emittance in order to phase mix damp the instability. The initial offsets of the beam were to be kept small in order to prevent a large saturated amplitude. Numerical simulations determined the initial criteria for the emittance profile and initial beam displacements. In order to demonstrate a final density depression of 25% of ambient pressure, at least five pulses with interpulse separation of 1- to 2-ms were specified.

Three different channel diagnostic instruments were prepared for the Fall and Winter 1989--1990 Advanced Test Accelerator (ATA) multi-pulse-propagation experiments. The first diagnostic consisted of an eight-beam laser deflection measurement of channel density profiles and time histories. Reduced density channels were observed under a variety of accelerator operating conditions. The magnitude, size, and position of these channels were measured and are explained on the basis of the prevailing beam conditions. The second diagnostic, consisting of optical emission measurements of beam currents and channel temperatures, confirmed previous observations of shorter optical Faraday cup pulses and, under some operating conditions, behavior uncorrelated with beam bug signals. The latter observations may be related to beam hose instabilities. Vibrational temperatures deduced from the optical fluorescence signals also show a trend of increasing during the later pulses in a burst. The third diagnostic, a CO{sub 2} interferometer designed to measure on-axis conductivity levels, was built but not deployed. 21 refs., 22 figs., 9 tabs.