Enhancement of radical generation in a round helium atmospheric-pressure plasma jet by an on-time modulated power source

Summary form only given: Atmospheric-pressure plasma jet (APPJ) has attracted tremendous attention in the past decade mainly due to its low cost and flexibility without the use of expensive vacuum equipment. It has found numerous applications such as surface cleaning, surface modification, thin-film deposition and recently biomedical applications that may include sterilization, blood coagulation, cell growth enhancement and wound healing, to name a few.In this paper, a round APPJ device is developed and tested. This APPJ consists of four parts: a silicon tube, a stainless steel tube, an aluminum tube and an aluminum ring. Powered electrode, which includes a stainless steel tube and an aluminum tube, is placed inside the silicon tube. The grounded electrode (aluminum ring) is wrapped around at the surface of silicon tube with some proper distance from the powered electrode (aluminum tube) inside the silicon tube. An AC power source of 60 W with a frequency of 25 kHz is applied to this APPJ with different high-voltage on-time settings. Optical emission spectrometer (OES) and a mercury thermometer are used for measuring the OES and gas temperature in the jet region at various downstream locations, which is important for biomedical applications. Helium (99.99%) is used as the working gas with a flow rate of 4 slm. Gas composition analysis using gas chromatography (GC) shows that an appreciable amount of impurities including oxygen and nitrogen (more than 20ppm) is found. Corresponding Reynolds number based on the average speed and inner diameter of the silicon tube is 1,392, which is a typical laminar pipe flow. Results show that, with a longer high-voltage on-time applied voltage setting, the jet plume length can increase up to 30 mm with appreciable gas heating in the discharge and in the jet region. In addition, the measured OES (optical emission spectra) shows that atomic oxygen, hydroxyl radical and nitric oxide can be enhanced more than 10-30 times as compared wi- h the standard voltage input. Simulation shows that appreciable amount of ambient air (not dry) is entrained into the discharge region in the silicon tube, which is directly linked to the production of hydroxyl oxide. More important findings will be presented in the meeting.