Kinetic modeling of the α to γ transition in radio frequency discharges

An accurate and comprehensive self-consistent kinetic model is applied to a helium radio frequency (rf) discharge which in experiments exhibits an ‘‘α to γ’’ transition. The main conclusions are (i) there is good agreement (factor of 2) between the experiment and simulation in plasma density, power density, and current density across two orders of magnitude of the applied voltage. (ii) The bulk electron temperature exhibits a transition from high at low driving voltages to low at high voltages. The low-voltage regime exhibits a larger bulk electric field in the simulation. (iii) Multistep ionization is important under all conditions studied.