CESIUM DEPLETION IN POSITIVE COLUMN OF CS-AR DISCHARGES

The longitudinal electric field and the electron density and temperature have been measured in the positive column of low-pressure dc arc discharges in mixtures of cesium and argon at densities around 5×1018 and 5×1022 m-3, respectively. The measurements have been made with electrostatic probes and with a microwave interferometer. At a low discharge current cesium alone is ionized. When the discharge current is increased the cesium atom density is reduced by ionization and radial diffusion, and at a critical current a discontinuous transition to a state having a high electron temperature is observed. This discontinuity is explained as the result of a multivaluedness of the electric field as a function of the current density. Even at the present low degree of ionization the electron mobility is found to be strongly influenced by Coulomb collisions. © 1969 The American Institute of Physics.