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We have developed a technique for absolute measurements of electron density in pulse-repetitive microwave discharges in air. The technique is based on the time-resolved absolute intensity of a nitrogen spectral band belonging to the Second Positive System, the kinetic model and the detailed particle balance of the N2C3Πu (ν = 0) state. This new approach bridges the gap between two existing electron density measurement methods (Langmuir probe and Stark broadening). The electron density is obtained from the time-dependent rate equation for the population of N2C3Πu (ν = 0) using recorded waveforms of the absolute C3Πu → B3Πg (0-0) band intensity, the forward and reflected microwave power density. Measured electron density waveforms using numerical and approximated analytical methods are presented for the case of pulse repetitive planar surface microwave discharge at the aperture of a horn antenna covered with alumina ceramic plate. The discharge was generated in air at 11.8 Torr with a X-band microwave generator using 3.5 μs microwave pulses at peak power of 210 kW. In this case, we were able to time resolve the electron density within a single 3.5 μs pulse. We obtained (9.0 ± 0.6) × 1013 cm-3 for the peak and (5.0 ± 0.6) × 1013 cm-3 for the pulse-average electron density. The technique presents a convenient, non-intrusive diagnostic method for local, time-defined measurements of electron density in short duration discharges near atmospheric pressures. [ABSTRACT FROM AUTHOR]

In this article the refraction effects in the weak shock wave (SW) dispersion on an interface with a temperature variation between two mediums are described. In the case of a finite-gradient boundary, the effect of the SW dispersion is remarkably stronger than in the case of a step change in parameters. In the former case the vertical component of velocity for the transmitted SW (the refraction effect) must be taken into account. Results of comparative calculations based on the two-dimensional model corrected for the refraction effect show significant differences in the shapes of the dispersed SW fronts. [ABSTRACT FROM AUTHOR]

In this paper we are presenting the full characterization of a supersonic flowing CO2/N2/Ar discharge at static pressures of 1–20 Torr and Mach number 2.15. In all aspects besides the flow speed and gas temperature, these conditions correspond to Martian entry plasma. Plasma parameters were determined by optical emission spectroscopy techniques. The gas and vibrational temperature were found from analysis of the rotational and vibrational spectra of the CO B 1Σ+-A 1Π Ångstrom system, respectively. The electron density was determined from the absolute intensity of the N2 C 3Πu-B 3Πg second positive system. A kinetic model for the discharge was developed to calculate the electron density and compared with experimental data. [ABSTRACT FROM AUTHOR]

Detailed characterization of a microwave cavity discharge in the supersonic flow of Ar/H2/Air mixtures at static pressures of 1–10 Torr and Mach number 2 is mostly based on emission spectroscopy techniques. In the conditions close to real combustion environments, effects of hydrogen and air admixture to plasma parameters and population of excited species in the discharge are demonstrated. The effects resulting in ionization loss are discussed from the aspects of dominant mechanisms and consequences for the plasma assisted hydrogen oxidation. [ABSTRACT FROM AUTHOR]

The refraction effects in the weak shock wave (SW) dispersion on an interface with a temperature variation between two mediums are studied. The results of comparative calculations based on the two-dimensional model corrected for the refraction effect have shown major differences in the shapes of the dispersed SW fronts.

Supersonic flowing C[O.sub.2]/[N.sub.2]/Ar discharge at static pressures of 1-20 Torr and Mach number 2.15 is characterized. Plasma parameters are determined by optical emission spectroscopy methods and a kinetic model for the discharge is developed for calculating the electron density.

Microwave cavity discharge in the supersonic flow of Ar/[H.sub.2][Air mixtures and its characterization based on the emission spectroscopy techniques are described. The effects seen with addition of [H.sub.2] into Ar plasma and with addition of air into Ar/[H.sub.2] plasma is discussed.

Results of hydrogen Balmer line-shape study on microwave-induced plasma discharges operated with pure hydrogen and with argon-hydrogen or helium-hydrogen mixtures are reported. Findings show that in both cases, the emission profiles of the Balmer lines did not show excessive broadening.

A tomographic numerical method based on the two-dimensional Radon formula for a cylindrical cavity has been employed for obtaining spatial distributions of the argon excited levels. The spectroscopy measurements were taken at different positions and directions to observe populations of excited species in the plasmoid region and the corresponding excitation temperatures. Excited argon states are concentrated near the tube walls, thus, confirming the assumption that the post discharge plasma is dominantly sustained by travelling surface wave. An automated optical measurement system has been developed for reconstruction of local plasma parameters of the plasmoid structure formed in an argon supersonic flowing microwave discharge. The system carries out angle and distance measurements using a rotating, flat mirror, as well as two high precision stepper motors operated by a microcontroller-based system and several sensors for precise feedback control. [ABSTRACT FROM AUTHOR]