NONEQUILIBRIUM ELECTRICAL CONDUCTIVITY OF A POTASSIUM-SEEDED ARGON PLASMA

Experiments have been made on the electrical conductivity of a nonequilibrium, potassium-seeded argon plasma at atmospheric pressure. The gas is heated uniformly in a vacuum heater up to a temperature of 1700°C. Electric field in the plasma is determined by electrostatic probes as a function of the current density through the plasma, which ranges from 10-5 to 2A/cm2. For small current density, the plasma is in thermal equilibrium and the conductivity is independent of the current density. The average momentum transfer cross section between electron and potassium atoms estimated from the equilibrium conductivity is 2.3 × 10-14 cm2. As the current density is increased the conductivity decreases, reaches a minimum, and then increases. When the current density is not small, the plasma is not in thermal equilibrium and the distribution function of electrons is not Maxwellian. The decrease of the conductivity is explained by considering inelastic collisions between electrons and potassium atoms and the radiation loss from the plasma. The apparent conductivity at large current density is much higher than the equilibrium value, although the uniformity of the current density was not assured.