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An atmospheric-pressure helium plasma generated in a 2.45-GHz microwave-induced cylindrical plasma torch has been investigated. The atmospheric-pressure helium plasma can be ignited at a microwave power of less than 400 W and sustained at as low as 100 W, at a gas flow of 50 L/min. The electron temperature Te, electron density ne, and gas temperature Tg measured by optical emission spectroscopy are 0.28-0.5 eV, 1015-1016 cm-3, and 1000-2000 K, respectively, at a power of 200-400 W and a gas flow rate of 20-50 L/min. In addition, it is noted that Te ≈ Tv (vibrational temperature) >; Tg ≈ Tr (rotational temperature) for these experiment parameters. These results show that the helium plasma generated in this atmosphericpressure plasma torch is in partial local thermodynamic equilibrium (pLTE).
Date of Publication: Dec. 2012