Parameters of microwave discharge plasmas in powder mixtures

Abstract

A study is made of the optical emission spectra of a plasma produced under the action of a microwave beam with a field amplitude of about 3 kV/cm on a metal-dielectric mixture at atmospheric pressure. In the initial stage of the discharge, the plasma is localized in microscale sites at the target surface, the characteristic size of the glowing regions in the target plane being less than 1 mm. In this stage, the target material is evaporated and atomic spectral lines with excitation energies of up to 6–8 eV are emitted. The population temperature of the excited levels, which was determined from the intensity ratios of atomic spectral lines, can be interpreted as the temperature of the atmospheric-pressure plasma. The temperatures determined from different pairs of lines belonging to the same or different elements (Cu, Mo, Li, Fe) fall within the range 7000–9000 K. In the later stage of the discharge, when the characteristic plasma size reaches a few centimeters, no atomic lines are present in the spectrum, which corresponds to a Planckian continuum with a temperature of 2400–3200 K.