Diagnostics for Metastable species and Electric Field in ns pulse PLASMAS Complementary diagnostics for measuring densities of metastable species in low- and high-pressure plasmas, and electric fields have been developed. ps Electric Field Induced Second Harmonic (EFISH) used for electric field measurements in a fast ionization wave in a discharge tube for N2 plasmas. EFISH signal is generated in the discharge tube wall, can be used for E-field measurements at low pressures, in capillary tubes, and helium plasma jets. Laplacian front Ionization front Quasi-steady-state discharge N2(A3Σu+,v=0-2) density after a ns pulse discharge burst E-field in a fast ionization wave in nitrogen (wave speed 0.4 cm/ns) DOE Plasma Science Center Control of Plasma Kinetics HIGHLIGHT March 2019 1

DISCHARGES IN BUBBLES IN HIGH VISCOSITY LIQUIDS Discharges in bubbles in hydrogels were investigated as a means to investigate plasma generation on and interaction with water-based gels. Repeatable discharges were produced in an argon bubble in hydrogel. Emission from OH (306.4 nm) results from plasma-surface interactions. Stronger OH band emission in the positive (needle) polarity than in the negative polarity. Fast OH emission decay due to collisional quenching. Current studies focus on the mechanical effect of discharge on bubble (e.g. oscillations, motion) and its dependence on gel viscoelasticity. Spectra of OH 306.4 nm band for a discharge in Ar bubble in positive and negative polarities. Experimental set up and typical voltage and current traces DOE Plasma Science Center Control of Plasma Kinetics HIGHLIGHT March 2019 2