A one-dimensional fluid simulation of a 13.56 MHz argon glow discharge including metastable species was performed as an example of a coupled glow-discharge/neutral-transport-reaction system. Due to the slow response time of metastables ( -10 ms) direct time integration of the coupled system requires -lo5 rf cycles to converge. This translates to prohibitively long computation time. An "acceleration" scheme was employed using the Newton-Raphson method to speed up convergence, thereby reducing the computation time by orders of magnitude. For a pressure of 1 Torr, metastables were found to play a major role in the discharge despite the fact that their mole fraction was less than 10V5. In particular, metastable (two-step) ionization was the main mechanism for electron production to sustain the discharge. Bulk electric field and electron energy were lower, and a smaller fraction of power was dissipated in the bulk plasma when compared to the case without metastables. These results suggest that neutral transport and reaction must be considered in a self-consistent manner in glow discharge simulations, even in noble gas discharges. 3668
Over the past few years multidimensional self-consistent plasma simulations including complex chemistry have been developed which are promising tools for furthering our understanding of reactive gas plasmas and for reactor design and optimization. These simulations must be benchmarked against experimental data obtained in well-characterized systems such as the Gaseous Electronics Conference (GEC) reference cell. Two-dimensional simulations relevant to the GEC Cell are reviewed in this paper with emphasis on fluid simulations. Important features observed experimentally, such as off-axis maxima in the charge density and hot spots of metastable species density near the electrode edges in capacitively-coupled GEC cells, have been captured by these simulations.
A particle-in cellldynamic Monte Carto simulation technique was developed to study the spatiotemporal electron dynamics in radio-frequency glow discharges. The electric field profile in a parallel plate one-dimensional geometly was obtained from a self-consistent fluid simulation. Using this profile, the particlein-celVdynamic Monte Carto simulation yielded the spatiotemporal electron velocity distribution function between the electrodes. A strongly electronegative chlorine discharge and an electropositive argon discharge were considered. At a pressure of 100 mTorr, the distribution function was non-Maxwellian except at the midgap of the chlorine discharge. The tail of the distribution was strongly modulated inside the sheath. Electron 'pile-ups' near the walls, charge double layers and negative plasma potential during part of the cycle were observed in the electronegative discharge at 13.56 MHz. lime-average results from the particle-in-cell/dynamic Monte Carlo simulation matched the fluid simulation favourably, even at a local Knudsen number Kn % 1, with differences confined mainly to the volume around the plasmahheath interface.
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