Nitrogen fixation using a Propeller Arc in air A novel plasma source (Propeller Arc or PA) utilizes a rotating cathode with a fixed anode to investigation basic plasma mechanisms governing N2-O2 reactions in air plasma. Peak NOx production efficiency with the PA is ~7×1016 molecules/J at 112 mA. Varying conditions enables investigation of mechanisms. One goal is to understand why air plasma NOx production efficiency varies with average E/N, this PA scaling with PNOx ~78(E/N)-0.85. Average E/N = (U/d)/((P/P0)/(T/T0)*N0) U: average discharge voltage (V) d: gap distance (m) P: gas pressure (atm), P0= 1 atm T: gas temperature (K), T0= 300 K N0: gas density, 2.43*1025 molecules/m3 Sony Cyber-shot, DSC-RX100 IV, 1000 fps, 1 ms Time-resolved images (15 Hz) Efficiency varies with average E/N DOE Plasma Science Center Control of Plasma Kinetics HIGHLIGHT July 2018 1

FLUID DYNAMICS DRIVE SELF-ORGANIZATION OF STREAMERS IN A BUBBLE Using a 2-dimensional plasma-in-liquid test cell, 2-D capillary waves initiated by streamer discharges have been observed. Chaotic streamers initially striking at the plasma-liquid interface act as forcing function. The streamers excite of dominantly capillary wave oscillations propagating along the bubble interface which provides feedback to the streamers. The oscillations lead to self- organization of the locations at which streamers strike the interface, which in turn further enhances the dominant oscillation mode. Back-lit interfacial capillary oscillations DOE Plasma Science Center Control of Plasma Kinetics HIGHLIGHT July 2018 2