Spatially Resolved Temperature Measurements of Atmospheric-Pressure Normal Glow Microplasmas in Air

The rotational and vibrational temperatures of DC normal glow air discharges were measured by comparing modeled optical emission spectra of the N₂ second positive system with spectroscopic measurements from the discharges. By using an imaging spectrometer and optical assembly, the temperature measurements were spatially resolved to about 6 mum. Results are presented for a 3.8-mA discharge at an electrode spacing of 400 mum. Rotational temperatures are highest in the near-cathode region around 1500 K and decrease toward the anode to about 1100 K. Throughout the discharge, higher rotational temperatures correspond with lower vibrational temperatures. The maximum vibrational temperature measured is around 5000 K. Emission from the N₂ ⁺ first negative system was also measured and is only intense in the negative glow (NG) region. The temperature near the anode is sensitive to the anode material. Gold, stainless steel, and tungsten electrodes were studied. Oxidizing anode materials can create a bright and hot anode spot several hundred kelvin warmer than for nonreacting anode materials. In addition, comparisons between spatially resolved and previously studied emission-averaged temperatures indicate that the emission-averaged temperatures correspond to those of the NG regions.