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

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 - nder different conditions (power, flow rate and gas combinations) are measured and analyzed.