A capacitive discharge in water vapour in the pressure range 133–150 Pa was studied. The discharge is an effective ecologically pure source of OH* hydroxyl emission in the VUV and UV spectral range (A  2Σ+ → X  2Π transition). The time profiles of densities of plasma species at different values of reduced electric field (E/N) were calculated using a kinetic model of the discharge. It is shown that E/N ∼ 190–200 Td is a breaking field for water vapour plasma, and with an increase in E/N a transition from electronegative to electropositive plasma takes place. The primary positive ions in the water vapour plasma are H3O+ ions, and the primary negative ions are OH− ions.

No abstract

Plasma jets are increasingly used in plasma medicine, in microelectronics and for surface treatment due to their unique properties, such as low gas temperature and high concentration of active species. This paper presents the results of a study of plasma jets generated by the atmospheric pressure dielectric barrier discharge while passing through it of argon-air, helium-air and helium-water vapor mixtures. Comparison of the plasma jets characteristics shows that the gas flow rate at which the maximum power of UV radiation is achieved increases in the series of He-H2O, He-air, Ar-air. Replacing Ar-air working mixture with He-air mixture leads to an increase in the plasma jet radiation power in ∼ 3 times. The maximum overall radiation power achieved in the He-air plasma jet was 0.07 W. The emission spectra of the plasma jets were identified in the spectral region of 270–900 nm, it was found that the molecular bands of the second positive and first negative systems of nitrogen predominate in the UV region of spectrum and lines of He I or Ar I prevail in the visible region. The distributions of the radiation intensity of excited plasma species along the jet length were measured. The analysis of difference in the emission spectra of the plasma jet in pure Ar and He and in their mixtures with air, as well as in a He-H2O mixture, has been performed taking into account values of the mean electron energy and rate constants of elementary processes in the plasma calculated using the Bolsig + code. The molecular and ionic reactions responsible for emission of radiation in the UV range of spectrum are considered.

The determination of plasma parameters in RF capacitive discharges enhanced by an external magnetic field using emission spectroscopy, double Langmuir probes and thermocouple methods is reported. The gas temperature, rotational temperature of CH radicals, electron temperature, and charged particle and atomic hydrogen densities as functions of the discharge parameters are determined. The system operating parameters can be adjusted in the following ranges: gas pressure in the discharge chamber 0.1 - 10 Pa; discharge power 80 - 200 W; magnetic field strength 0 - 200 G. Pure methane and pure argon, as well as mixtures of methane and argon in various proportions were used as working gases. In addition, carbon films were deposited on glass substrates and their optical properties were investigated. It is shown that the external magnetic field has a significant influence on both plasma parameters and properties of the deposited films.

In a previous study, the characteristics of plasma generated by fast electrons behind a grid anode with short glow discharge were studied using numerical simulation. The source of the post-anode plasma electrons is considered to be the direct current glow discharge itself in the gap between a cathode and a grid anode. However, the electron attenuation of the microwave radiation in the post-anode space measured in experiments does not correspond to the numerical predictions. In this paper, the current–voltage characteristics of the short glow discharge with a grid anode and the spectral characteristics of the discharge in both the electrode gap and the space behind the grid anode are studied; the effective thickness of the plasma in the post-anode space is estimated using a spectral method.