Design and preliminary characterization of a miniature pulsed RF APGD torch with downstream injection of the source of reactive species

The design of a miniature low-power atmospheric pressure glow discharge torch (APGD-t) and the results of its preliminary electrical and spectroscopic characterization are presented. A capacitively-coupled pulsed RF (13.56 MHz) helium plasma jet is formed in a converging confinement tube and O-2 is injected downstream in the plasma afterglow region through a capillary electrode. With 1 SLM He, the APGD-t produced a non-thermal plasma jet of 500 mu m-diameter and approximate to 2.5 mm-long at power levels ranging from 1 to 5 W. At approximate to 1 W, the gas temperature and He excitation temperature near the nozzle exit were approximate to 50 degrees C and slightly below 2000 K, respectively. The breakdown voltage in 1 SLM He is approximately 220 Vpk-to-O. Careful electric probe measurements and circuit analysis revealed the strong effect of the voltage probe on the total load impedance. The injection of 10 SCCM O-2 through the capillary electrode led to the transport of atomic O further downstream in the plasma jet and to a slight increase of the He excitation temperature without significant effects on the electrical properties and jet length. Alternatively, the addition of an equivalent amount of O-2 (1 v/v%) to the plasma-forming gas affected the electrical properties slightly, but led to a drastic contraction of the plasma jet. The atomic oxygen production and transport conditions provided by the APGD-t are promising for precise bio-applications such as the treatment of skin tissues and cells.