Emission spectroscopy characterization of electrode species in the freestream flow at the NASA Ames miniature Arc Jet II facility

Abstract

The second generation miniature Arc Jet (mARC II) is a subscale arc jet at NASA Ames Research Center that is undergoing initial characterization. During its operation, the electrodes used to produce continuous plasma flows deteriorate and the flow purity decreases. The present work reports the use of optical emission spectroscopy as a characterization tool for impurities in the plasma flow. The discussion is focused on the interpretation of spectroscopic measurements and their evolution under different testing conditions. Special emphasis is given to copper, the main atomic element of the anode, and to atomic oxygen and atomic nitrogen, two major components of air plasma. The highest rate of anode deterioration is found to occur during the arc jet ignition. Based on the experimental spectra, a preliminary numerical characterization of the plasma temperature, enthalpy and number density is conducted.