A 0.9 to 1.5 kW, 2.45 GHz atmospheric pressure air microwave plasma torch has been operated efficiently with less than 1 % reflected power. The plasma is sustained in a 28 mm internal diameter fused quartz tube which penetrates perpendicularly through the wide walls of a tapered and shorted WR-284 (72 x 17 mm cross-section) waveguide. A study has been made of the effects of power and airflow on the electronic excitation temperature, T exc. Abel inversion of radial profile chord averaged Fe I emission lines in the 370 to 377 nm range have been used to obtain localized profile measurements of T exc inside the waveguide excitation region. In general, temperature profiles peak on axis with no evidence of a skin effect in the large diameter (10 mm FWHM emission intensity) plasmas. A maximum central T exc of 6550 K ± 350 K is observed at an airflow rate of 28 lpm. When maintaining a constant flow rate of 14 lpm, a 55 % increase in microwave power from 0.9 to 1.4 kW causes a ~100 % increase in plasma volume without any noticeable effect on the central T exc value. At a constant microwave power of 1.4 kW, an increase in total flow rate from 11 to 28 lpm decreases the volume of the plasma by ~25 % and increases the central T exc by ~13 %. The axially peaked temperature profiles are consistent with an electron density of ~ 10 13 cm-3 .
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