A 3.0 GHz pulsed microwave source operated at atmospheric pressure with a pulse power of 1.4 MW, a maximum repetition rate of 40 Hz, and a pulse length of 3.5 µs is experimentally studied with respect to the ability to remove NOx from synthetic exhaust gases. Experiments in gas mixtures containing N2/O2/NO with typically 500 ppm NO are carried out. The discharge is embedded in a high-Q microwave resonator, which provides a reliable plasma ignition. Vortex flow is applied to the exhaust gas to improve gas treatment. Concentration measurements by Fourier transform infrared spectroscopy confirm an NOx reduction of more than 90% in the case of N2/NO mixtures. The admixture of oxygen lowers the reductive potential of the reactor, but NOx reduction can still be observed up to 9% O2 concentration. Coherent anti-Stokes Raman scattering technique is applied to measure the vibrational and rotational temperature of N2. Gas temperatures of about 400 K are found, whilst the vibrational temperature is 3000-3500 K in pure N2. The vibrational temperature drops to 1500 K when O2 and/or NO are present. The randomly distributed relative frequency of occurrence of selected breakdown field intensities is measured by a calibrated, short linear-antenna. The breakdown field strength in pure N2 amounts to 2.2×106 V m-1, a value that is reproducible within 2%. In the case of O2 and/or NO admixture, the frequency distribution of the breakdown field strength scatters more and extends over a range from 3 to 8×106 V m-1.

Pulsed microwave discharges operated at atmospheric pressure in gas mixtures containing N 2 , O 2 , and NO are investigated experimentally and theoretically for various gas mixture constituents and operating conditions with respect to the ability of exhaust gas purification. The rotational gas temperature and the vibrational temperature of N 2 are derived from CARS measurements. The composition of the exhaust gas after treatment is monitored using FTIR spectroscopy. The processes of the chemical, electronic, and vibrational kinetics are described by a model that has been developed to calculate the species densities. The results obtained show that in N 2 /NO gas mixtures an overall reduction of NO x takes place. In the case of N 2 /O 2 /NO gas mixtures, no net reduction of NO x is achieved for a pulsed microwave power below 3600 W, a pulse length of 50 μs, and a typical repetition frequency of 2 kHz.

The vapor nucleation of argon was investigated in shock tube expansions starting from room temperature. The cooling from the superheated initial state to nucleation onset was attained in unsteady flow fields at high Mach numbers M=5. Thermodynamic states for homogeneous nucleation were observed between 30 and 180 Torr at corresponding temperatures in the range of 50–70 K. The high starting temperatures do not affect the nucleation onset states compared to previous experiments on the subject, where the expansions started from much lower temperatures. The slight differences in the onset states to previous experiments employing cryogenic shock and Ludwieg tubes may be attributed to the higher cooling rates and to nonisentropic expansion effects.

A coherent anti-Stokes Raman scattering (CARS) set-up has been developed to study the reduction of nitric oxide (NO) by a microwave-generated nitrogen plasma under atmospheric pressure. A frequency-doubled Nd:YAG laser provides two pump beams at nm and excites a dye laser, which is tunable between 588 and 615 nm. Density and temperature profile measurements of in the cylindrical microwave discharge by the common CARS technique deliver an axis temperature of 7000 K at P = 800 W input power. The detection of a minority of NO in under atmospheric pressure by CARS is limited to a concentration of 2500 ppm. By applying polarization-sensitive CARS the detection limit can be scaled down to 200 ppm. This technique is used to examine the reduction of NO in a reaction chamber fed by vibrationally excited and N entering the chamber through a nozzle. Behind the nozzle most of the NO is decomposed. An overall reduction efficiency for NO of 65-85% was found, decreasing with growing NO concentration.

A coherent, anti-Stokes Raman scattering (CARS) setup has been developed to detect contamination of atmospheric nitrogen by nitric oxide (NO). To allow spatially resolved measurements and the possibility of utilizing windows close by the test volume, we chose the folded BOXCARS setup with a CARS lens of focal length 0.5 m and a diameter of 80 mm. A frequency-doubled Nd:YAG laser (lambda = 532 nm; E-L = 50 mJ; tau(L) = 10 ns; repetition rate, 10 s(-1); bandwidth, 0.05 cm(-1)) serves as pump for a dye laser (E-p = 25 mJ; E-L = 2 mJ; bandwidth, 0.03 cm(-1)), which is tunable between 585 and 615 nm. Nitric oxide CARS spectra including the first hot band have been measured with high spectral resolution in a temperature range from 300 to 800 K. The detection limit of NO is on the order of 0.25% in nitrogen under atmospheric pressure. With suppression of the nonresonant background in the application of polarization CARS, the detection limit could not be scaled down in a desirable manner, The comparison between measured and calculated CARS spectra of NO in an N-2 surrounding confirms the reliability of the energy matrix elements and the Lorentzian width of the type Gamma(p,T = 0.06(298 K/T)(0.6)p/p(0) cm(-1).

The formation of argon clusters by homogeneous nucleation of pure argon diluted in helium was investigated in the supersonic outflow of a shock tube, where the clusters were detected by laser light scattering from the particles in supersaturated states. The thermodynamic states for the onset of homogeneous nucleation varied between 48 and 85 K with corresponding argon partial pressures in the range 2–850 Torr. Values of adiabatic supercooling with respect to the argon phase equilibrium ranged between 3 and 10 K. The experiments are in agreement with previous investigations in subsonic shock tube and supersonic Ludwieg tube expansions but disagree with previous investigations in steady supersonic nozzle expansions. It is possible to explain qualitatively the observed differences in argon nucleation behavior on the basis of a thermodynamic and kinetic concept independent of the basic assumptions of existing nucleation theories.

Measurements of the fundamental ac-susceptibility provide a sensitive tool to study the shielding behavior of ceramic high-T c superconducting material. In this work, ac-susceptibility data for differently prepared YBaCuO-samples are presented. From the data, information can be extracted about an effective grain size, which is not necessarily identical to the optically determined particle size. It is demonstrated that the data allow an estimation of the bulk quality which depends strongly on the preparation conditions.