Control of plasma spatial distribution in gas discharge lamps filled with alkali metal vapors

The thermodynamic properties of alkali metal vapor plasma in the pressure range 0.25 - 3.0 atm and temperatures 1500 - 60000 K are considered. It is shown that a distinctive feature of this plasma is the existence of a relatively narrow critical temperature interval in which the plasma consists only of electrons and singly ionized atoms. The specific heat capacity of the plasma has a minimum value in the critical temperature range, corresponding to the heat capacity of a simple e-i plasma in which the second ionization of atoms has not begun. It has been shown that, due to this property, in gas discharge lamps filled with alkali metal vapors, it is possible to control the type of spatial distribution of the plasma. Under relatively low currents, when the temperature of the plasma doesn’t reach the critical range of the value, the traditional space distribution of the plasma is realized in the gas discharge tube. In this case, most of the plasma is concentrated in the axial region of the tube and its concentration decreases along the radius from the axis to the walls of the tube. With sufficiently high currents, when the plasma temperature on the axis exceeds the values from the critical interval, the opposite case is realized: the main part of the plasma is now concentrated on the periphery of the gas discharge volume. In this case, the plasma concentration increases along the radius from the axis to the tube walls. It is shown that the transformation of one type of spatial distribution of plasma into another occurs when the plasma temperature on the axis reaches values from the critical interval and the specific heat capacity approaches its minimum value, corresponding to a simple plasma consisting of electrons and single-charge ions.

Investigation of the plasma composition of a discharge with a self-heating hollow cathode and an active anode in a gas mixture with titanium and hexamethyldisilazane vapors

The analysis of composition of low-pressure (~0.1-1 mTorr) hollow cathode arc plasma in Ar+N2 gas mixture with Ti+hexamethyldisilazane vapors was carried out by optical emission spectroscopy. The influence of HMDS flow rate (1-10 g/h), discharge current (10-50 A) and Ti-vapors flow on hexamethyldisilazane decomposition degree and plasma composition and was investigated. The proposed plasma activation method provides both an intense flow and a high activation degree of metal vapors, and a sufficient decomposition degree of precursor vapors for the formation of solid TiSiCN coatings at a high deposition rate. Test coatings with a thickness of 6 microns and a hardness of 31 GPa were obtained in 1 hour at 400ºC.

Azide Method for Generating Metal Vapors in Space

Modern methods of rocket research of the upper layers of the atmosphere and near-Earth space cannot be imagined without the use of glowing artificial clouds (GAC). Traditional pyrotechnic methods for generating vapors of alkali and alkaline earth metals, used for the formation of GAC in space, are ineffective and require, as a rule, the use of metals with high chemical activity. The article presents the results of studies on the development of an alternative method for generating vapors of alkali and alkaline earth metals to create GAC in near-Earth space using inorganic azides of the corresponding metals. The long-term use of pyrotechnic metal vapor generators to create GAC in the upper atmosphere, equipped with azide pyrotechnic compositions, confirmed their high efficiency, reliability and safety of use.

Thermodynamics and transport properties of the supercritical fluid of metals

The proposed model allows to calculate the composition, thermodynamic and transport properties of the supercritical metal vapors within unified approach. The model includes atoms, immersed in jellium, and thermally ionized electrons and ions. The jellium is the part of the bound states electron density. The density of electron jellium increases with the compression of atomic gas and does not depend on temperature directly. At compression, the electrical conductivity passes through the minimum from the conductivity of thermal electrons to the conductivity of electrons of jellium accordingly. Calculations of the equation of state and the electrical conductivity of supercritical metal vapors agree well with physical and numerical experimental data.