On-Line Measurement of Ion Density in Atmospheric Nitrogen Discharge Filaments via Radiation Signals from Plasma Oscillation*

Diagnosis of the particle number density of plasma plays an important role in the understanding of plasma sources and processing. Regular radiation signals from plasma oscillation in filaments of atmospheric nitrogen discharge, which were excited by the injection of secondary electron beams during the propagation of the streamer, are employed to determine the ion density of plasma and its evolution in the filaments. Results show that the density of N I in a filament of atmospheric nitrogen discharge is of the order of 1013 cm-3. It is also found that the recombination processes play a dominant role in plasma decay, and that the ion density decreases non-monotonically with time during streamer propagation.