Electrical Breakdown in High-temperature Gases

Abstract

RELATIVELY few experimental results are available for the breakdown of high-temperature gases at atmospheric pressure and above. Alston¹ has confirmed Paschen's law for air up to 1,100° C and obtained flashover voltages which were independent of electrode material. On the other hand, it is well known from investigations of the decaying properties of freely recovering arcs² that ‘thermal’ breakdown can occur at considerably reduced voltages while the charge concentration remains high and the electrodes retain their heat. Similar low voltages of breakdown have been observed in shock tube investigations³. Forman⁴ has recently described experiments with rare gases up to 300 mm pressure and for refractory cathodes at temperatures up to 3,000° K. The cathode was a filament of 0.01-in. diameter and the concentric anode had a diameter of 1 cm. Breakdown occurred at anode voltages considerably lower than the ionization potential of the gas for argon and xenon and cathode temperatures greater than 2,400° K, but was not observed for helium. Although the gas in the immediate vicinity of the cathode was assumed to be in thermal equilibrium at the cathode temperature, the bulk of the gas and certainly the anode were considerably cooler.