PARTICLE SIMULATIONS OF RADIOFREQUENCY GLOW-DISCHARGES

Particle-in-cell simulations are used to study the structure of radio-frequency (RF) glow discharges in helium between parallel-plate electrodes. We have examined a range of conditions and report on a variety of observed phenomena. Comparisons to experiment and analytical models are made, when possible. The differences between discharges in which secondary electrons play a key role in sustaining the discharge and those in which secondary electrons are unimportant are examined in three cases which illustrate the importance of the discharge-sustaining mechanisms. Electron-energy distributions are found to be, in general, non-Maxwellian, with shapes that depend in complex ways on discharge conditions. In the absence of secondary electron emission, electron heating in the sheath regions of the discharge is enhanced at higher voltages compared to ohmic heating in the bulk of the plasma. Fast electrons accelerated by the advancing sheath can carry a substantial fraction of the conduction current in the bulk of the discharge, reducing the effective bulk ohmic heating of electrons. Ion-energy distributions at electrode surfaces have been predicted and are compared to experimental measurements. Simulations indicate that ion power deposition scales as the square of the applied voltage, while electron power deposition scales approximately linearly with applied voltage. Discharge power is dominated by ion losses at higher voltages. These results are in good agreement with predictions from analytical models of RF discharges.