In the present work, an argon microwave (2.45 GHz) plasma flame created at the end of a surface-wave-sustained discharge column in a helium environment has been experimentally studied. This is a plasma with new possibilities because under some experimental conditions it expands, being less contracted than the plasma flame created in open air. The new expanded discharge could offer additional advantages for applications in which larger extensions of plasma were required. The expansion phenomenon of this plasma flame was studied under different experimental conditions. In every case, the characteristic parameters of this expanded plasma such as electron density, electron and gas temperatures, or density population of excited atomic levels were measured by using optical emission spectroscopic techniques. From these results, the main advantages of this plasma source were pointed out.
M. C. García, M. Varo, and P. Martínez, "Spectroscopic Study of an Expanded Argon Microwave (2.45 GHz) Plasma at Atmospheric Pressure in a Helium Environment," Appl. Spectrosc. 63, 822-829 (2009)