Dj. Spasojević

Advanced fit technique for astrophysical spectra Approach insensitive to a large fraction of outliers

Aims. The purpose of this paper is to introduce a robust method of data fitting convenient for dealing with astrophysical spectra contaminated by a large fraction of outliers. Methods. We base our approach on the suitable defined measure: the density of the least squares (DLS) that characterizes subsets of the whole data set. The best-fit parameters are obtained by the least-square method on a subset having the maximum value of DLS or, less formally, on the largest subset free of outliers.

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.

Simultaneous plasma and electric field diagnostics of microdischarge from hydrogen Balmer line shape

Hydrogen Balmer beta line shape from a microhollow gas discharge in argon with traces of hydrogen is used for simultaneous diagnostics of plasma and cathode sheath parameters. Simple model of relevant processes responsible for line broadening is developed and results favorably compared with experiment at 500 mbar with the electron density 3.8×1020 m−3 and electric field strength of 127 kV/cm in the cathode sheath region.

Spectroscopic application of an iterative kinetic cathode sheath model to high voltage hollow cathode glow discharge in hydrogen

We present a simple one-dimensional iterative kinetic model of the cathode sheath region of high voltage, low-pressure hydrogen hollow cathode discharge. The models convenience as a supplemental diagnostic tool is demonstrated by determining the most relevant discharge parameters through an analysis of the spectral shape of the hydrogen Balmer alpha line recorded along the axis of a cylindrically symmetrical high voltage low-pressure hollow cathode glow discharge in hydrogen. Thus, an effectively one-dimensional approach is tested and shown to give satisfactory spectral lines fits with reasonable values for discharge parameters, most notably the gas temperature.

A contribution to spectroscopic diagnostics and cathode sheath modeling of micro-hollow gas discharge in argon

In this paper, the hydrogen Balmer beta line shape from a micro-hollow gas discharge (MHGD) in argon with traces of hydrogen is used for simultaneous diagnostics of plasma and cathode sheath (CS) parameters. For this purpose, a simple model of relevant processes responsible for the line broadening is introduced and applied to the Balmer beta profile recorded from a MHGD generated in the microhole (diameter 100 μm at narrow side and 130 μm at wider side) of a gold-alumina-gold sandwich in the pressure range (100–900 mbar). The electron number density Ne in the range (0.4–4.5) × 1020 m–3 is determined from the width of the central part of the Balmer beta line profile, while, from the extended wings of the Balmer beta profile, induced by dc Stark effect, the next three parameters are determined: the average value Ea of electric field strength in the CS in the range (16–95 kV/cm), the electric field strength E0 at the cathode surface in the range (32–190 kV/cm), and the CS thickness zg in the range (18–70 μm)...

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.