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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 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 average static (dc) electric dipole polarizabilities of the NaK and KCs heteronuclear alkali dimers have been measured, and those of the homonuclear molecules remeasured using molecular beam deflection in an inhomogeneous electric field. A congruent magnetic field enabled removal of the monomer constituents of the beam. The resulting deflection curves reflect both the permanent electric dipole force (for the heteronuclear dimers only), and the induced (polarizability) dipole force. It is assumed that the molecular constituents of the beam possess modified Maxwell–Boltzmann velocity and rotational state distributions. A Mach number is introduced to describe the sonic beam properties. The data analysis consists of a two-parameter least squares best fit of the experimental deflection curves to computed ones, the parameters being the polarizability and the Mach number. Values of the permanent heteronuclear dipole moments are taken from the literature. The obtained static electric dipole polarizabilities in units of (Å3) are 34±3 for Li2 (948 K), 40±3 for Na2 (676 K), 77±6 for K2 (542 K), 79±6 for Rb2 (527 K), 104±8 for Cs2 (480 K), 51±3 for NaK (612 K), and 89±5 for KCs (488 K). Comparison with recent calculations as well as earlier measurements of the homonuclear species are given. Two empirical rules are proposed for determining polarizabilities and dipole moments of heteronuclear molecules. [ABSTRACT FROM AUTHOR]

We have measured the average electric dipole polarizabilities of twenty alkali halide dimers, using a molecular beam electric deflection method. This is a continuation of the earlier measurements of five alkali halide dimers [R. Kremens et al., J. Chem. Phys. 81, 1676 (1984)]. We compare our measurements with a simple combination of bond (via a ‘‘spring’’ model) and effective ionic polarizabilities, using literature values for the required molecular constants. Agreement between our measured and calculated values is reasonable, in most cases, considering the relative crudeness of the model. [ABSTRACT FROM AUTHOR]

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]

An innovative type of subcritical streamer discharge, generated by bursts of focused microwave (MW) radiation in transverse electromagnetic mode with wavelength of 10 cm, pulse duration of 40 µs, and intensity of 5.6 × 10[sub 4] W/cm², was initiated at the surface of a polymer foil at 420 Torr in air. The MW field of a quasioptical beam was three times lower than the critical breakdown field. Exposure of a polymer foil to the discharge caused a transition from hydrophobicity to hydrophilicity. [ABSTRACT FROM AUTHOR]