Spectroscopic temperature measurements of air breakdown plasma using a 110 GHz megawatt gyrotron beam

Temperature measurements are presented of a non-equilibrium air breakdown plasma using optical emission spectroscopy. A plasma is created with a focused 110 GHz 3 μs pulse gyrotron beam in air that produces power fluxes exceeding 1 MW/cm2. Rotational and vibrational temperatures are spectroscopically measured over a pressure range of 1–100 Torr as the gyrotron power is varied above threshold. The temperature dependence on microwave field as well as pressure is examined. Rotational temperature measurements of the plasma reveal gas temperatures in the range of 300–500 K and vibrational temperatures in the range of 4200–6200 K. The vibrational and rotational temperatures increase slowly with increasing applied microwave field over the range of microwave fields investigated.