Plasma physics

• Fundamental parameters of the gas discharge plasma at conditions typical of the developed high-power deep ultraviolet, visible, and mid-infrared, such as gas temperature and  electron temperature have been determined. The distribution of gas temperature along the radius of a nanosecond pulsed longitudinal discharge was determined theoretically at the cases of uniform and non-uniform power input in the discharge. The thermal conductivity of binary gas systems was calculated for the case of gas discharges in He and Ne with small admixtures of copper, bromine, hydrogen and strontium. Analytical solution of the steady-state heat conduction equation is found. The average gas temperature is found by averaging the radial gas temperature distribution over the radius. By measuring the relative intensities of some He and Ne spectral lines, originating from different upper levels, the average electron temperature in the developed gas discharge tubes was evaluated.

• The processes in the plasma of a hollow cathode discharge (HCD) used for laser excitation were studied experimentally and by modeling. The optimal ratio of the cathode length and diameter at which the discharge is homogeneous in the whole discharge volume was defined. As a result, the excitation efficiency of a HCD sputtering copper ion laser was improved and higher laser output power was achieved. Based on the obtained results a new (patent protected) multi-cathode laser construction was designed. An analysis of the species behaviour and reactions for a HCD excited in a He–Ar–Cu mixture was made. A reduced chemistry module was developed, simplified by reducing the number of species and reactions. The model can be used in optimization studies of glow discharges in general. A kinetic Monte-Carlo model is developed describing the electron behaviour in a HCD by following closely the electrons while they travel and collide in the discharge. Results of the electron energy distribution function, the mean electron energy and the distribution of the ionization events in the discharge volume under typical discharge conditions, are obtained. The results from the kinetic model demonstrate that due to the high concentration of energetic electrons in the whole discharge volume, the HCD is very appropriate medium for excitation and ionization of laser ablated material for elemental analysis. Based on the results of modeling, a discharge tube for combination of laser ablation and emission analysis in a hollow cathode discharge was designed. The research was in the frame of joint projects with Antwerpen University, Belgium and Eindhoven Technical University, The Netherlands.

• The interaction of plasma media in HCD with external light, including laser light were investigated. The spontaneous coherent conductivity in a negative glow was observed and ascribed to the self-aligned excited states. It is an integral galvanic manifestation of the spontaneous coherence. Deconvolution of experimental dynamic opto-galvanic signals in the glow plasma of HCD was done. The signals were fitted with theoretical determined function and the decay lifetimes of the states, taking part in the processes, which were responsible for the signal creation at different discharge currents.