Modeling neutral dynamics in pulsed helium short-gap spark discharges

A numerical analysis of the neutral dynamics is performed in the case of helium short-gap spark discharges to show the energy memory effect of recurring discharges. The millimetric (4 mm) and submillimetric (0.3 mm) discharges are studied at atmospheric pressure and ambient temperature (293 K). This corresponds to a neutral density of 25x10(25) m(-3). The maximum injected power is either 50 or 3 W with a duration of 1 mu s, the relaxation time between the two successive injections is 5 mu s, The evolution of the neutral gas is described with the classical transport equations written in a two-dimensional cylindrical geometry with plane electrodes and solved with powerful numerical schemes. The effect of the discharge an the neutral gas is represented by energy and momentum transfers. The neutral gas is no longer considered as an infinite sink dissipating the energy of the electrons and ions acquired from the field. It is shown that the energy and momentum transfer effects initiate and control the variations of temperature, pressure, and neutral population. Concerning the recurring aspect, the neutral memory effect persists during the time lapse between two successive discharges and directly influences the gas dynamics of the following discharge. The specific behavior of the gas dynamics for the shorter gap (0.3 mm) is also discussed in terms of boundary effects, In particular, the influence of the latter on the velocity field is studied. (C) 1996 American Institute of Physics.