PLASMA DIAGNOSTICS IN AIR PLASMAS CONTAINING WATER DROPLETS Production of reactive nitrogen species (RNS) in water was demonstrated using atmospheric pressure plasmas through water droplets. Optical emission spectroscopy confirmed that gas phase RNS were generated under humid, high-speed airflow and high power conditions. Low pH values in the treated water suggested that water droplets efficiently captured RNS from the gas phase. Typical optical emission spectrum from an air plasma containing water droplets at two different powers. Evolution of pH in initially deionized water with non-equilibrium air plasma treatment. DOE Plasma Science Center Control of Plasma Kinetics HIGHLIGHT January_2018 1

ATMOSPHERIC PRESSURE PLASMA JET WITH CO-AXIAL SHIELDING GAS The plasma chemistry and plasma-surface interactions in APPJs depend on the ambient gas (most often air) entrained by the jet. To achieve better control of the system outcomes a co-axial shielding gas may be employed – N2 in this example The mole fraction of the contaminant in the ambient gas (O2 here) was reduced by increasing the shielding gas flow rate. The electron density at the end of a 60 ns pulse peaks over the powered pin electrode (P) and along the line separating He and N2. (top) He mole fraction in APPJ with N2 as the shielding gas and air as the ambient . (bottom) Electron density at the end of a 60 ns 5 kV pulse. P is the powered pin electrode. DOE Plasma Science Center Control of Plasma Kinetics January_2018 HIGHLIGHT 2