Spatial Characterization of the Atmospheric-Pressure Moderate-Power He Microwave-Induced Plasma

Abstract

Three-dimensional emission profiles of several metallic and nonmetallic elements from a moderate-power (450 W) atmospheric-pressure helium microwave-induced plasma (He MIP) are presented. A torch using a tangential flow for plasma centering was developed, but the initial goal of forming a stable annular plasma was not achieved. Helium emission gave a symmetrical distribution with maximum emission in the center of the plasma both radially and longitudinally. Calcium atomic emission reached its longitudinal maximum about 3 mm from the cavity bottom and was radially much broader than most nonmetals. The maximum metal ionic emission occurred about 6 mm above the cavity bottom. Maximum chlorine emission occurred still higher and was not affected by nebulized water in the plasma. Emission distribution and behavior suggests that different excitation mechanisms exist for metals and nonmetals.