TIME RESOLVED STUDY OF THE BULK PLASMA OF A 13.6 MHZ DISCHARGE IN ARGON

Time dependent population densities of excited states of Ar and Ar+ have been measured by time and space resolved optical emission spectroscopy in an asymmetric parallel plate plasma reactor in Ar at an excitation frequency of 13.6 MHz. Time averaged ion densities in the plasma have been determined by a floating double probe. At pressures above 20 Pa and at distances from the powered electrode beyond the emission intensity maximum the population densities are modulated with essentially the fundamental RF frequency. In order to explain this experimental result the bulk plasma was modelled under the assumption that the local electric field is the sum of a time dependent part oscillating with the fundamental frequency and a constant part of similar size. For the calculations, the electron Boltzmann equation and a set of rate equations were simultaneously solved in a fully time dependent way. The observed modulations of the emission intensity of the spectral line of Arl at 516.23 nm and of the calculated level population of the emitting 6d(1/2)1 state agree within the experimental errors.