Time-resolved measurements of the gas temperature in a H2/CH4 medium pressure microwave 915 MHz pulsed plasma

Experimental measurements of the time variation of gas temperature in a non-equilibrium hydrogen-methane microwave plasma operating at medium pressure and under pulsed mode are presented. The hydrogen plasma is created using a 915 MHz microwave generator at an input microwave power up to 17 kW and the gas temperature is determined from the rotational distribution of the G 1 Σ g + excited state of H 2 ( T (G)). In continuous discharge, the rotational temperature T (G) of H 2 (G 1 Σ g + ) is found to be nearly equal to the gas temperature determined from rotational distribution of the a 3 Π u metastable state of C 2 molecule obtained from absorption spectroscopy. The time evolution of H 2 (G 1 Σ g + ) rotational distribution in pulsed discharges reaches a Boltzmann equilibrium only 100 µs after the beginning of the pulse. Variations of the T (G) in-pulse value as a function of pressure, volumetric power density and gas velocity is studied.