Electrical Properties of Inert Gas Plasmas Generated in Thermionic Cold-Cathode Diodes by Radiation in a Nuclear Reactor

Abstract

The electrical properties of inert gas (Xe, Kr, Ar) plasmas have been studied in a nuclear reactor environment at gamma radiation dose rates up to 6×108 rad/h. The measurements are made by inserting a gas-filled thermionic diode into the core of a 5-MW nuclear reactor. The space-charge neutralization effects caused by the ion-electron pairs generated in the gas are measured and interpreted in terms of plasma properties of the gas. The electrical conductivity of the plasma, at a constant radiation level, goes through a maximum as a function of pressure in the range of 1–300 Torr. If the radiation dosage is varied, keeping all other factors the same, one finds the electrical conductivity monotonically increases with dose rate in the range of 106−6×108 rad/h. Experiments are described which indicate that electrons can be removed from a low work function ``cold'' electrode into the plasma by a mechanism different from either thermionic or field emission. A physical model is proposed to explain this phenomenon.