(351d) Experimental Diagnostics and Modeling of Microplasma Discharges

High pressure (100s of torr) microplasma (length scale 100s of microns) non-equilibrium discharges have potential applications in chemical microreactors, sensors, microelectromechanical systems (MEMS), and excimer radiation sources. Experimental and theoretical studies of these microplasmas can provide critical information on fundamental discharge characteristics, and help extend the window of stable discharge operation. Spatially resolved measurements (resolution ~ 5 microns) were taken across a 200 micron slot-type microdischarge in atmospheric pressure helium or argon. Small amounts of actinometer gases were added to the flow for optical emission spectroscopy measurements. Gas temperature profiles were determined from N2 emission rotational spectroscopy. Stark splitting of the hydrogen Balmer-beta line was used to investigate the electric field distribution in the cathode sheath region. Electron densities were determined from the spectral line broadening of H-beta emission. Despite the tremendous power loading (~50 kW/cm3), the gas temperature was relatively low due to the high surface-to-volume ratio of the microreactor. The gas temperature in He was significantly lower (350-550 K) than that in Ar (over 1000 K), a reflection of the much higher thermal conductivity of He. Increasing the gas flow rate had little effect on the gas temperature in He, but significantly reduced the gas temperature in Ar. This is consistent with the fact that conductive heat losses dominate in the helium microdischarge, while heat losses by convection play a major role in the Ar microdischarge. Gas heating had a strong effect on the electric field profiles in the negative glow and the anode sheath. A plasma flow simulation of the microdischarge, including a comprehensive chemistry set, was also performed. The experimental findings were in agreement with the simulation predictions.