Experimental characterization of a section of a spherically imploding plasma liner formed by merging hypersonic plasma jets

Abstract: We report experimental results on merging of hypersonic plasma jets, which is the fundamental building block for forming spherically imploding plasma liners as a potential standoff compression driver for mangeto-inertial fusion. Jets are formed and launched by contoured-gap coaxial plasma guns mounted at the six spherical chamber. First, from experiments with two and three merging jets of four different species (N, Ar, Kr, Xe), we show that (1) density spatial non-uniformities can be large (with electron-density jumps ranging from 2.9 for N to 6.6 for Xe) when shocks form upon jet merging, but smaller (density jumps <2) when shocks do not form; (2) jet impurities (20% Ti in these experiments) can increase the level of density spatial non-uniformity by increasing the collisionality of jet merging; and (3) the liner Mach number can remain high (>10), as required for plasma liners to be an effective compression driver. Second, from experiments with six and seven merging jets using Ar, we present results with improved jet-to-jet balance of <2% across jets, including (1) evidence of substantially increased balance in the jet merging and symmetry of the liner structure, and (2) potentially favorable changes in the jet-merging morphology with the addition of the seventh jet. For both experiments, we present comparison between experimental and synthetic data from three-dimensional hydrodynamic codes.