Global models of pulse-power-modulated high-density, low-pressure discharges

Global (volume-averaged) models of high-density, low-pressure electropositive and electronegative discharges are described both for continuous wave (CW) and for pulsed-power excitation. Argon and chlorine discharges are treated. The particle and energy balance equations are applied to determine the charged particle and neutral dynamics. For argon just after the power has been turned on, the analysis shows an initial very sharp rise in electron temperature T-e, followed by a decay of T-e and an increase in the electron density n(e) to steady state values during the pulse-on time. Just after the power has been turned off, T-e decays rapidly and n(e) decays more slowly. The time-average n(e) can be considerably higher than that for CW discharges for the same time-average power. For chlorine, a CW discharge is highly dissociated and the negative ion density n(Cl)- is lower than n(e). For a pulsed discharge, the initial rise and subsequent decay of n(Cl)- just after the power has been turned off are determined analytically. A pulsed discharge can have the same neutral radical (Cl) flux to the walls for a reduced average power. The analytical models are compared to more complete global model simulations and to experimental observations. We find that global models can provide considerable insight into the discharge dynamics.