Steady RF discharge regimes and LF instability

The phenomena have been studied in the gas-discharge gap accompanying the occurrence of the nonmonotonous behavior of the active RF current in the discharge circuit in the noble gases. In the central part of the RF low pressure discharge in argon the region of nonmonotonous behavior of plasma density is observed. At low argon pressures this phenomenon accompanies the nonmonotonous behavior of the active RF current whereas at intermediate pressures these two phenomena exist in different RF voltage ranges. The nonmonotonous behavior of the plasma density is accompanied by LF noises and regular oscillations of increased amplitude (ionization instability). The nonmonotonous behavior of the plasma density and the regular oscillations manifest themselves most brightly in pure argon, whereas at concentrations of air in argon of more than 80% this phenomenon is not observed. The phenomena studied are attributed to the screening of RF field by the regions of enhanced plasma density at the boundaries of electrode layers. The authors suggest to continue the region of RF discharge α - γ hybrid regime to lower pressures and smaller gaps. RF frequency f = 13.56 MHz, p = 10-2 - 10 Torr. The spacing between plane stainless steel electrodes of 100 mm diameter was changed in the limits L = 7--54 mm. RF voltage was fed to one of the electrodes and another electrode was grounded