Development of Schlieren Imaging and Interferometry to Diagnose Density Profiles in a DPF

The MJOLNIR (MegaJOuLe Neutron Imaging Radiography) dense plasma focus (DPF) at LLNL is designed to perform neutron radiography of dynamic events. The DPF (2.6 MA, 1 MJ stored energy) consists of two coaxial electrodes, which generate a plasma sheath by ionizing deuterium gas. The sheath implodes on the axis in a z-pinch geometry. When the pinch breaks apart, it produces a beam of ions that impacts the "target", a region of the sheath assembled on axis past the pinch (n_e ~1e19/cm^3). The beam-target interaction produces a neutron burst. A laser interferometry diagnostic will measure the electron density of the pinch and target regions; allowing us to infer the ion density in the target region, study dynamics during implosion to optimize beam generation in the pinch region, and. compare with hybrid fluid-kinetic particle-in-cell stimulations to verify models. Our implementation of the interferometer began with a Schlieren imaging system, the results of which we present here. The Schlieren technique allows us to image density gradients in the plasma, putting upper and lower bounds on the density and showing small-scale features and structure in the plasma. LLNL-ABS-836612