Neutral particle density transients in gaseous discharges

A model is presented which describes the neutral density transients in gaseous discharges. It is shown that the duration of the initial density transient is governed by the speed of sound in the gas in which the discharge is produced. The development of the gas-flow velocity pattern in the discharge tube is a consequence of the interplay between three competing volume forces: (a) the driving volume force, which is generated by the interaction of the charged particles with the neutral particles, (b) the viscosity force, and (c) the neutral pressure gradient force. The influence of the geometry of the discharge tube on the neutral particle density transients is also discussed. The initial neutral particle density transient is believed to be the origin of acoustic resonances observed in rf-excited gaseous discharges.