N. M. Šišović

Electric field distribution in the cathode-fall region of an abnormal glow discharge in hydrogen: experiment and theory

We present the results of an experimental and theoretical study of the electric field distribution in the cathode-fall (CF) region of an obstructed abnormal glow discharge in hydrogen. The distribution of electric field strength was measured using an improved Stark polarization spectroscopy technique of the hydrogen Balmer beta line profile. The developed technique extends field measurements to the low-field region while remaining in good agreement at larger field strengths with the well established Stark polarization peak separation electric field measurement technique. The experimental electric field distribution is modeled by a simple analytical formula, adopted after consideration of elementary processes relevant in the CF. It fits the experimental distribution within error bars and consequently enables determination of the CF parameters such as its thickness and the mean free path for electrons in the CF region.

Doppler spectroscopy of hydrogen Balmer lines in a hollow cathode water vapour and argon–water vapour glow discharge

The results of Doppler spectroscopy of hydrogen Balmer lines in a stainless steel (SS) and copper (Cu) hollow cathode (HC) water vapour and argon–water vapour glow discharge are reported. The experimental profiles in water vapour discharge are fitted well by superposing three Gaussian profiles. The half widths of narrow and medium Gaussian are, in energy units, 0.2–0.5 and 3–4 eV for SS HC and 0.14–0.38 and 2.7–3.7 eV for Cu HC which is expected on the basis of earlier electron beam → H2O vapour experiments. The half width of the largest Gaussian in water vapour is 22 eV and 13 eV for SS and Cu HC, respectively. In argon–water vapour discharge three Gaussians are also required to fit experimental profiles. While half widths of narrow and medium Gaussians are similar to those in water vapour, the half width of the largest Gaussian is 37 eV and 28 eV for SS and Cu HC, respectively. The half widths of the largest Gaussian in water vapour and in argon–water vapour mixture indicate the presence of excessive Doppler broadening. The differences in width of the excessively broadened part of the line profiles with SS and Cu HC in water vapour and in argon–water vapour mixture are explained as a consequence of oxide formation at the cathode surface. This study is an attempt to extend and compare our earlier investigations of anomalous Doppler broadening in HC discharge operated with hydrogen isotopes or hydrogen mixtures with inert gases to hydrogen containing inorganic molecules.

Excessive broadening of hydrogen Balmer lines for discharge-surface interaction monitoring

A comparative study of the hydrogen Hα line shapes in titanium and stainless steel hollow cathode discharges, run with hydrogen or argon–hydrogen mixture illustrates the possibility of using the excessively broadened part of line profile for heavy particle-cathode surface interaction monitoring.

Ar I and Ne I spectral line shapes for an abnormal glow discharge diagnostics

We report the results of an Ar I and Ne I line shape study in an abnormal glow discharge operating in argon and neon. The spectral lines were observed along the axis of a cylindrical glow discharge parallel (side-on) and perpendicular (end-on) to the cathode surface. The side-on spectra show spectral line shifting and sometimes simultaneous shifting and splitting in the cathode fall region of the glow discharge. The results of the measured line shift with available data for the dc Stark effect are used for measurement of electric field strength in the cathode fall region of the glow discharge. Electron temperatures of 2860 K and 4770 K in the negative glow region of argon and neon discharges, respectively, were determined from the relative intensities of Ar I or Ne I lines using the Boltzmann plot technique. An electron number density of ≈1020 m−3 (±25%) in the negative glow region of the argon discharge was determined from the widths of two plasma-broadened Ar I lines using theoretical Stark broadening data. The end-on recorded line profiles show 10–40% larger half-widths than the side-on recorded line profiles from the negative glow. This effect is a result of the superposition of line emission in the cathode fall region under the influence of the dc Stark effect on the line profile from the negative glow.

Spectroscopic study of high energy excited deuterium atoms in a hollow cathode glow discharge

The presented results are concerned with the shape of the Balmer alpha line emitted from a low pressure dc glow discharge with stainless steel (SS) and titanium (Ti) hollow cathode (HC) with D2 or Ar∕D2∕H2 gas mixture. The analysis indicates that the line profile represents a convolution of three Gaussian profiles resulting from different collision excitation processes. The average energy of excited deuterium atoms determined from the width of the broadest Gaussian is about 86eV in both HCs. In Ar∕D2∕H2 gas mixtures, the energies are in the range from 33eVto47eV, but with much larger contribution of this Gaussian to the Balmer alpha profile. In discharges with hydrogen isotopes, the energy derived from the medium-width Gaussian is in the range from 4eVto6eV, while in gas mixtures it is between 1eV and 2eV. The width of the narrowest Gaussian slightly exceeds the instrumental broadening and it is always below 0.5eV.

Spectroscopic application of an iterative kinetic model of the cathode-fall region in a hydrogen abnormal glow discharge

We present an iterative kinetic model of the cathode-fall (CF) region in a hydrogen abnormal glow discharge, providing efficient calculations of electric field spatial distribution and distribution functions of H atoms and H+, and ions. The model is very convenient for spectroscopic applications because the knowledge of these distributions enables calculation of virtually all spectroscopic quantities of interest, which is illustrated here by comparison of model predictions and experimental electric field distribution, and hydrogen Balmer beta line shapes recorded end-on and side-on for various positions along the CF region of the discharge.

Spectroscopic diagnostics of microhollow gas discharge in hydrogen

Hydrogen Balmer beta line profile from a microhollow gas discharge (MHGD) in hydrogen is used for diagnostics of cathode sheath (CS) parameters. The profile was recorded from a MHGD microhole (diameter 100 μm at narrow and 130 μm at wider side) of a gold-alumina-gold sandwich in the pressure range (100–400) mbars. The average electric field strength in CS (25–46) kV/cm and CS thickness (60–120) μm were determined by profile fitting with the aid of model recently developed and used in argon MHGD.

Rotational and gas temperatures of molecular deuterium in a hollow cathode glow discharge

Abstract We report the results of optical emission spectroscopy measurements of rotational Trot and translational (gas) temperature of deuterium molecules. The light source was a low-voltage high-pressure hollow cathode (HC) glow discharge with titanium cathode operated in deuterium. The rotational temperature of excited electronic states of D2 was determined from the intensity distribution in the rotational structure of Q-branches of the two Fulcher-α diagonal bands: [ν′ = ν″ = 2] and [ν′ =ν″ = 3]. The population of the excited energy levels, determined from relative line intensities, was used to derive the radial distributions of the temperature of the excited and the ground state of the deuterium molecule.

Ne I spectral line shapes in Grimm-type glow discharge

We report the results of five Ne I line shapes study in an abnormal Grimm-type glow discharge operating in neon. The spectral lines were observed along the axis of a cylindrical glow discharge parallel (side-on) and perpendicular (end-on) to the cathode surface. The side-on spectra showed a spectral line shift and sometimes a simultaneous shift and split in the cathode fall region of the glow discharge. The results of the measured line shift with the available data for the dc Stark effect were used to estimate the electric field strength in the cathode fall region of the glow discharge. The end-on recorded line profiles showed up to 30% larger half-widths than the side-on recorded line profiles from the negative glow. This effect is a result of the superposition of line emission in the cathode fall region under the influence of the dc Stark effect on the line profile from the negative glow. In addition, wavy features at the far wing in the direction of dc Stark shift were detected. All observed phenomena related to end-on line shapes in Grimm discharge were related quantitatively to the dc Stark effect in the cathode fall region and plasma line broadening in the negative glow region.

On the use of two hydrogen bands for spectroscopic temperature measurement in a low-pressure gas discharge

Abstract We report the results of the optical emission spectroscopy measurements of rotational Trot and translational temperature Ttr of hydrogen molecules. The light source was hollow cathode glow discharge with titanium cathode operated in hydrogen at low pressure. The rotational temperature of excited electronic states of H2 was determined either from the relative line intensities of R branch of the GK → B band or from the P, Q and R-branches of the Fulcher-α diagonal band. The population of excited energy levels, determined from the relative line intensities was used to derive rotational temperature of the ground state of hydrogen molecule.