ELECTRICAL CONDUCTIVITY OF AN ARGON-POTASSIUM PLASMA AT LOW CURRENT DENSITIES AS A FUNCTION OF GAS TEMPERATURE

The electrical conductivity of a streaming argon-potassium plasma was measured as a function of the electric current density and compared with calculated values. The gas temperature varied from 1400°K to 2400°K, the potassium seed concentration from 0.1 to 0.5 per cent, and the maximum current density was 5 A/cm2. It was found that the value of the electron temperature at a current density j = 0 is strongly influenced by atom-atom excitation collisions. The unexpectedly high values of the electrical conductivity for current densities between 0 and 0.1 A/cm2 are due to a surplus of electrons carried from the hotter parts of the apparatus into the measuring channel. Calculations of electron density relaxation effects gave some idea, as well, of the efficiency of preionization. For values of j between 0.1 and 0.5 A/cm2 a contraction of the current in the measuring channel was observed. Hence the maximum in the current-voltage characteristic, not predicted by the theory, can be explained qualitatively. The influence of the gas temperature on the electrical conductivity for current densities between 0.5 and 5 A/cm2 is less than expected from the theory. The deviation, which are probably due to the uncertainties of the cross-sections used in the calculations, do not exceed 15 per cent.