A two-temperature chemically non-equilibrium model describing in a self-consistent manner the heat transfer, the plasma chemistry, the electric and magnetic field in a high-current free-burning arc in argon has been developed. The model is aimed at unifying the description of a thermionic tungsten cathode, a flat copper anode, and the arc plasma including the electrode sheath regions. The heat transfer in the electrodes is coupled to the plasma heat transfer considering the energy fluxes onto the electrode boundaries with the plasma. The results of the non-equilibrium model for an arc current of 200 A and an argon flow rate of 12 slpm are presented along with results obtained from a model based on the assumption of local thermodynamic equilibrium (LTE) and from optical emission spectroscopy. The plasma shows a near-LTE behaviour along the arc axis and in a region surrounding the axis which becomes wider towards the anode. In the near-electrode regions, a large deviation from LTE is observed. The results are in good agreement with experimental findings from optical emission spectroscopy.

This review describes the experimental studies of contraction in neon, argon and helium, discussing the basic regularities of the phenomenon. These studies, extended over a long time, are still urgent. For pressures that are not too high a noticeable contraction of the plasma glow and a smooth non-monotonic dependence of the degree of contraction on the current are observed. Above a critical pressure the plasma immediately contracts into a bright thin cord, if the current reaches a critical value. A hysteresis phenomenon is observed during the transition from the diffuse state to the contracted state and vice versa. Experiments that show the secondary role of non-homogeneous gas heating for contraction in neon and argon, and the main role for contraction in helium, are described. Studies of the ionization waves (the strata), which propagate as pulses of the current cord area, are reviewed showing the close relationship between contraction and stratification. The roles of various mechanisms leading to the contraction and describing the general picture of the observed phenomena are analysed. For heavy noble gases the main role is played by ionization non-linearity as a function of electron concentration, which is related to the competition of electron-atom and electron-electron collisions. This non-linearity leads to plasma shrinkage and the development of ionization instability in the radial (contraction) and longitudinal (stratification) directions. For helium such non-linearity does not play a leading role, since the frequency of the elastic electron-atom collisions is considered to be constant over a large energy range, and this yields a Maxwellian distribution function. The contraction in helium is defined by thermal effects. In addition, recent studies on the numerical modelling of the contraction are discussed.

The replacement of mercury in conventional fluorescent lamps by other components is highly desirable for environmental reasons. This paper gives a short review of new types of mercury-free plasma light sources operating at low pressure. In particular, the features of cylindrical glow discharges in rare-gas mixtures including xenon are discussed, focusing on the generation of the 147 nm resonance radiation of xenon and its transition into visible light by new phosphors with sufficient efficiency. Laser absorption and vacuum ultraviolet emission spectroscopy are applied for several rare-gas mixtures to reveal the contributions of the different gas components and their excited states to the power balance and radiation output. The experimental research is assisted by theoretical studies applying self-consistent hybrid models of the cylindrical column plasma. The good agreement between experimental and theoretical results obtained at selected discharge conditions makes it possible to predict optimum discharge parameters by means of extensive model calculations. It is demonstrated that about half of the efficacy of a mercury fluorescent lamp can be reached if the rare-gas discharge is operated at pressures below 100 Pa.

Atoms in electronically excited states are of significant importance in a large number of different gas discharges. The spatio-temporal distribution particularly of the lower excited states, the metastable and resonance ones, influences the overall behavior of the plasma because of their role in the ionization and energy budget. This article is a review of the theoretical and experimental studies on the spatial formation and temporal evolution of metastable and resonance atoms in weakly ionized low-temperature plasmas. Therefore, the transport mechanisms due to collisional diffusion and resonance radiation are compared step by step. The differences in formation of spatio-temporal structures of metastable and resonance atoms in plasmas are attributed to these different transport mechanisms. The analysis is performed by obtaining solutions of the diffusion and radiation transport equations. Solutions of stationary and non-stationary problems by decomposition over the eigenfunctions of the corresponding operators showed that there is, on the one hand, an effective suppression of the highest diffusion modes and, on the other hand, a survival of the highest radiation modes. The role of the highest modes is illustrated by examples. In addition, the differences in the Green functions for the diffusion and radiation transport operators are discussed. Numerical methods for the simultaneous solution of the balance equations for metastable and resonance atoms are proposed. The radiation transport calculations consider large absorption coefficients according to the Lorentz contour of a spectral line. Measurements of the distributions of metastable and resonance atoms are reviewed for a larger number of discharge conditions, i.e. in the positive column plasma, afterglow plasma, constricted pulsed discharge, stratified discharge, magnetron discharge, and in a discharge with a cathode spot.

This paper presents an electrical arc model based on physical parameters of the arc including temperature, enthalpy, pressure, and also arc geometry. In this model, different mass flows and power losses are considered. The different powers including radiative and turbulent power as well as power gain and loss carried by axial and radial mass flows are calculated and simulated as a function of physical parameters. Moreover, the different arc diameter expressions and their influence on power losses are examined by arc experiments with high-speed imaging and arc dynamic behavior analysis. This model can provide the dynamic behavior of the arc easier in contrast to more complex physical models. The comparison with conventional arc models, such as Schwamaker, Habedank, Kema, and Schwarz, illustrates that the new arc model can better reproduce electrical measurements.