Spatio-temporal evolution of a pulsed chlorine discharge

A one-dimensional fluid model of a pulsed (square-wave power modulated) chlorine discharge was developed in order to study the spatiotemporal evolution of species densities and electron temperatures for various pressures, powers, pulsing frequencies and duty ratios. Simulation results show spontaneous separation of the plasma into an ion–ion core and an electron–ion edge during the power ‘on ’ (active glow) fraction of the cycle. A transition from an electron-dominated plasma to an ion–ion plasma occurs during the power ‘off ’ (afterglow) fraction of the cycle, under the conditions examined. The formation of an ion–ion plasma is favoured at lower power levels, higher pressures, and lower duty ratios. A minimum afterglow time is required for an ion–ion plasma to form and the negative ions to reach the walls. Increasing the afterglow period increases the fraction of time an ion–ion plasma is sustained in the reactor. The evolution of negative ion density profiles is especially complex due to the formation of self-sharpening fronts during power ‘on ’ and subsequent back-propagation of the fronts during the power ‘off ’ stage of the pulse. When possible, simulation results are compared to reported experimental data. In general, good agreement is obtained, except that the measured dependence of electron density on pulse period and duty ratio is more complex than predicted. 1.