Electron Density in Mixed Gas Plasmas Generated by Fission Fragments

Studies of electron density are reported for a quiescent neon-argon gas plasma generated by fission fragments in the core of a nuclear reactor. Reaction kinetic equations for the various ionic and excited species are solved self-consistently with electron-energy balance equations to yield values of electron density and temperature. It is shown that for containers of diffusion length of about 1.6 mm or greater, there exists a maximum value of electron density at a total gas pressure p≈90 Torr and [Ar]/[Ne]≈10−4; the dominant ion in this case is the atomic Ar+ ion. At low values of neutron flux (∼1010 cm−2 sec−1) and electron density (∼1010 cm−3), the electron temperature is computed to be at or near the gas temperature, but at high values of neutron flux (∼1013 cm−2 sec−1) and electron density (∼1012 cm−3), the electron temperature is higher than the gas temperature by an important amount (∼600°K). Inpile measurements of electron density using microwave techniques are in very good agreement with the theoretical predictions.