Nitrogen vibrational excitation in a N-2/He pulsed planar-ICP RF discharge

A pure inductive regime of pulsed RF discharge in N-2-He mixtures at 0.2 Torr has been investigated by time resolved Langmuir probe and optical emission spectroscopy. A planar coil ICP with a Faraday shield has been used. Mixture compositions of 5-100% N-2 and duty cycles, T-ON = 1-15 ms and T-OFF = 15 ins, have been explored. The Langmuir probe analysis evidences a Maxwell electron energy distribution in the discharge and post-discharge, characterized by electron density and temperature that depend on both duty cycle and composition. The vibrational excitation of N-2(C) state is inferred by the N-2 second positive emissions. Its kinetic analysis reveals the formation of a high vibrational excitation of ground state nitrogen. A vibrational temperature higher than 10 000 K can be reached at the end of the 5 ms discharge pulse on the levels v = 0-3 of the X state. Such a high vibrational temperature slows the post-discharge relaxation of the electron temperature.