Coherent Ion Plasma Oscillations in a DC Corona Discharge in Rarefied Air

Stable, nearly sinusoidal, phase-coherent ion plasma oscillations have been consistently observed superimposed on the dc levels of positive coaxial corona discharges at air pressures of the order of a few torr. The frequency of these oscillations, typically several hundred kilohertz, has been found to be a function of air density and dependent on the presence and concentration of gaseous trace contaminants. Various characteristics of these oscillations, a simplified theoretical model, and possible applications are discussed.