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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 1Σg+ excited state of H2(T(G)). In continuous discharge, the rotational temperature T(G) of H2(G 1Σg+) is found to be nearly equal to the gas temperature determined from rotational distribution of the a3Πu metastable state of C2 molecule obtained from absorption spectroscopy. The time evolution of H2(G 1Σg+) 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.