Experimental characterization of a section of a spherically imploding plasma liner formed by merging hyper-sonic plasma jets

Spherically imploding plasma liners are a proposed stand-off compression driver for magneto-inertial fusion. We report experimental results on the formation of a section of a spherically imploding plasma liner via the merging of up to seven hyper-sonic plasma jets launched by state of the art, contoured-gap, coaxial plasma guns. Previously, we described initial results on the merging of six plasma jets that had greater than 50 percent mass variation across the jets, leading to poor symmetry in the liner structure. This paper reports more comprehensive results with mass variation across jets of less than 2 percent, achieved by using improved gas valves in the plasma guns. A suite of diagnostics is used to characterize the section of the plasma liner formed by six merging plasma jets and provides evidence of increased balance in the merging plasma jets. We also report on experiments focused on the merging of two and three jets with variable initial angles and velocities to evaluate the merging effects on Mach number degradation due to shock ion heating and the formation and evolution of non-uniform density structures. Experimental data are used to benchmark simulation utilizing three-dimensional hydrodynamic codes. The diagnostic results indicate readiness for a 36 gun experiment to form a fully spherical imploding plasma liner that will provide data on peak ram pressure scaling and non-uniform density evolution.