Diagnostics of atmospheric pressure microwave generated micro-plasma by using optical emission spectroscopy

• Main Authors: Peiyao Liu, Grotjohn, Timothy A.
• Format: Conference Proceeding
• Language: English
• Subjects: Biomedical optical imaging; Cavity resonators; Discharges (electric); Microwave theory and techniques; Optical materials; Plasmas; Stimulated emission
• ISSN: 0730-9244; 2576-7208
• DOI: 10.1109/PLASMA.2014.7012596

Summary form only given. Portable low-cost microplasma sources received interest in the past decade due to their various applications including materials processing, biomedical and chemical analysis, and optical radiation sources.[1-5] In particular, for atmospheric pressure microwave microplasmas that do not require vacuum systems, it is possible to realize 3D motion operation and portable lower-cost operation. Further, by using higher frequency energy (radio frequency and microwave) to power the microplasma discharge, non-LTE (non-local thermodynamic equilibrium) plasmas have the advantage of reducing the erosion of electrodes and also producing high power density plasmas with reasonably low power consumption.In this investigation two microwave-powered microplasma systems are characterized using optical emission diagnostics. The first system is developed based on a double-strip-line structure. Top and bottom copper strip-lines are separated by a dielectric material. The structure is powered at one end and the plasma is formed at the other end where the two copper strip-lines are brought together to a gap with 250 microns separation. The feedgas is flowed through a channel in the dielectric such that it exits with the feedgas flowing into the gap created by the two strip-lines. The second system is constructed using a small foreshortened cylindrical cavity that has a hollow inner conductor and a small capacitive gap at the end of the cavity. The feedgas is flowed through a 2 mm inner diameter quartz tube which is located inside the hollow inner conductor of the cavity. Pure Argon, ArgonOxygen mixtures (up to 10% Oxygen) and Argon-Hydrogen (with 2% hydrogen) are used as feedgas. The microwave power used for the discharges varies from 5 to 60 Watts. The flow rate of the feed-gases varies from 900 sccm - 2100 sccm. The optical emission spectroscopy technique was used to diagnose the discharges. Plasma properties such as rotational temperatures and electron densities under different conditions (power, flow rate and gas combinations) are measured and analyzed.