Time-resolved investigations of pulsed microwave excited plasmas

Pulsed microwave excited (2.45 GHz) argon plasmas generated by a slot anten na type plasma source are investigated by various diagnostic tools. Through the combined use of time-resolved planar optical emission spectroscopy (TP OES), microwave interferometry (MWI) and Langmuir probes the temporal behav iour of the electron density, n(e)(t), and effective electron temperature, T-e(t), for the pulse frequency range of 0.2-20 kHz are measured. Additiona lly, from TPOES maps of Ar* and Ar+, the qualitative spatially and time-res olved electron temperature distribution is derived. The n(e)(t) and T-e(t) rise and decay times are almost constant throughout the examined frequency range. A n(e)(t) rise time of 1 ms and a decay time of 0.6 ms is derived fr om probe and MWI data at 5 Pa. A T-e(t) rise time between 5 and 10 mu s and a decay time between 50 mu s and 80 mu s is derived from TPOES and probe m easurements at 5 Pa. The maximum time-averaged electron density, (n) over b ar(e), at 5 Pa is obtained at a pulse frequency f of 200 Hz. With increasin g pressure and power the pulse frequency f at which a maximum of (n) over b ar(e) is reached decreases to f approximate to 50 Hz. The temporal n(e)(t) and T-e(t) behaviour for the investigated pressure range is described by a simple set of equations based on the 'Global Model' of pulsed plasmas. It c an be concluded that the electron loss rate nu(loss) controls both the rise and decay times of n(e)(t). The nu(loss) is in the first order a function of the plasma system dimensions and geometry. The decay of T-e(t) depends o n nu(loss) and the losses due to inelastic scattering.