Parameters of plasmaof high-current nanosecond dischargein air with small admixtures of copper vapor


Introduction. The use of a discharge in air of atmospheric pressure opens the possibility of developing windowless UV lamps that are promising for applications with significant mechanical overloads under various extreme conditions, since they do not contain any quartz elements (windows or bulbs). The output characteristics of such "point" lamps strongly depend on the plasma parameters of the nanosecond discharge with small admixtures of the vapor metal from which the electrodes are made. At present, there are no data on the parameters of air plasma with small admixtures of copper vapor under the operating conditions of a "point" lamp, which inhibits the establishment of mechanisms for populating the excited levels of atoms and copper ions in such a plasma. This in turn inhibits the long range optimization of the output characteristics of such "point" sources of UV radiation.
Purpose. The purpose of the study was to determine the emission characteristics in the spectral range of 200-250 nm of the plasma of high-current nanosecond discharge, between copper electrodes in air at atmospheric pressure under conditions of strong overstress of the discharge gap and to carry out a numerical simulation of the parameters of the plasma of air with small copper impurities under conditions close to those realized in the experiment.
Methods. The nanosecond discharge in air of atmospheric pressure between copper electrodes was ignited. The distance between the copper electrodes was 1 mm, which led to the ignition at atmospheric pressure air of a "point" diffuse discharge of a spherical shape with a diameter of 1 mm. The standard program was used to solve the Boltzmann kinetic equation for the electron energy distribution function (EEDF) for modeling air plasma atmospheric pressure parameters with small copper vapor admixtures, since under the experimental conditions the maximum value of the E/P parameter reached about 530 V cm-1 torr-1 , which is less than the critical value of E/P for nitrogen according to the local electron runaway criterion 590 V cm-1 torr-1.
Results. Numerical simulation of the plasma parameters established that for the range of reduced electric field strength 610 Td-810 Td, at which experimental studies of the characteristics of a "point" nanosecond discharge were carried out, mean electron energies varied within the range of 12.2-15.6 eV; the value of the electron concentration was 10.7·1021 m-3 – 8.7·1021 m-3 at a current density of 765·106 A / m2 on the surface of the copper electrode. The excitation constants of the 2P3/2,1/2, 2D3/2 , 2D5/2 , 4F7/2 , - states of the copper atom and its ionization were in the range (7.3 – 8.5) 10-13 m3/c, ( 0.29 – 0.28) 10-13 m3/c, ( 0.22 – 0.22) 10-13 m3/c, (0.19 – 0.22) 10-15 m3/c and (0.33 – 0.45) 10-13 m3/c, respectively. The maximum excitation rate constant for nitrogen molecules was for the sum of the singlet states: they were (1.4 10-14 ) m3/s for an electric field strength of 810 Td. The specific losses of the discharge power in the plasma on inelastic collisions of electrons with the components of the gas mixture were maximal for nitrogen molecules and reached 32% for excitation of the sum of singlet nitrogen states.
Conclusion. Radiation of the plasma is concentrated in a narrow spectral interval of 200-250 nm, is promising for use as a "point" UV lamp; the spectral lines 248.9 and 254.4 nm Cu II are promising for estimating the electron temperature in a plasma. Mean electron energy, electron mobility, specific electric power losses and the rate constants of elastic and inelastic scattering of electrons by copper, argon and carbon dioxide, oxygen and nitrogen molecules, the ratio of which was 3: 7.098: 0.266: 159.157: 593.438, depending on the magnitude of the reduced electric field (ratio of the electric field strength (E) to the total concentration of atoms and gas molecules (N)). The range of changes in the parameter E / N = 1-1300 Td (1∙10-17 – 1∙10-15 V∙cm2 ) and included the values of the parameter E / N, which were realized in the experiment (610-810) Td

Keywords: nanosecond discharge, copper, air, emission spectrum, ultraviolet, electron temperature and density, spec ific losses of discharge power, rate constants of electronic processes

10.24144/2415 8038.2018.43.89 95