Generation of Microwave Capillary Argon Plasmas at Atmospheric Pressure

A technique has been developed to generate stable Ar plasmas at atmospheric pressure inside of a quartz capillary tube. The microwave plasma in the capillary tube is produced by utilizing a single mode resonant circular cavity applicator with 2.45 GHz frequency excitation. The plasma can be confined or fully exposed outside the cavity as plasma jets depending on the operating conditions. The profile of the plasma front has been characterized as a conical tip or split branching jet plume. The measured discharge length and the power density of the plasma range from 6 to 10 cm and 35 to 75 W · cm
^-3
, respectively. Addition of CH
₄
into the Ar plasma results in an increase in the abundances of excited CN and C
₂
carbon radicals and a concomitant decrease in the intensity of the Ar emission.