Browsing by Author "Hartigan, Patrick M"

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    Exploring Supersonic Magnetized Astrophysical Flows with Numerical Simulations and Multiple Experimental Techniques on the OMEGA Laser
    (2017-11-27) Liao, Andy Sha; Hartigan, Patrick M
    Gas and magnetic fields play codominant roles in the dynamics of many astrophysical plasma flows in the Galaxy. Technological advances in magnetic field generation have only recently opened these strong-field regimes to high energy laser astrophysics experiments. To investigate astrophysical magnetized supersonic flow interactions in the controlled environment of the laboratory, we took advantage of the new capability of the MIFEDS pulsed-power generator to magnetize supersonic plasma flows we produced using the OMEGA laser in a series of scaleable experiments. Our experimental campaigns on OMEGA recreated three different astrophysical scenarios involving magnetized supersonic flows. The first of these produced an analogue of a magnetized star-forming cloud undergoing collapse and fragmentation following the passage of a strong shock. The second of these produced an analogue of magnetospheric accretion flows on young stars. In this thesis we elaborate on the third of these in which a supersonic plasma flow from a laser drive was directed against a magnetized wire. Combined, our apparatus makes an analogue of stellar wind interactions with a planetary magnetosphere. To diagnose the plasma in our experimental analogue of planetary magnetospheres, we employed a tetrad of state-of-the-art plasma diagnostics. The two-plasmon decay imager is a gated instrument that produces two-dimensional still images from nanosecond-timescale exposures of the plasma's optical self-emissions; we use the gated optical imager to reveal the large-scale structure of the evolving plasma. The streaked optical pyrometer functions as a streak camera that we use to produce a continuous history of the plasma's optical self-emissions that are spatially resolved in a single axis. We use a monoenergetic proton radiography technique to projectively image the plasma's magnetic field independently from the gas. We use spatially-resolved Thomson-scattering spectroscopy to directly probe the structure of the plasma's interfaces. To recover the dynamics of the experimental plasma from the diagnostic data, we assembled a numerical toolkit to help reconstruct the evolution trajectory of the plasma from first principles. Our toolkit includes Eulerian hydrodynamics codes AstroBEAR and FLASH; we use the IONMIX routines to implement realistic materials and radiative transfer in our global hydrodynamical simulations of the laser drive. We use the particle-in-cell code EPOCH to model the plasma kinetics. Combining numerical simulations and composite instrumentation, we determined that radiative ablation of the wire ahead of the directed inflow from the laser drive produced outflowing gas that helped to advect magnetic flux into an overdense layer concident with a hydrodynamical shock. In this case, our experimental analogy extends beyond that of a conventional planetary magnetosphere to that of an evaporating, weakly and poorly magnetized exoplanet. Consequently, in the weakly and poorly magnetized regime our experiments show that seed magnetic fields from the MIFEDS generator can still be used as a tracer of plasma interfaces revealed by proton radiography; they help show the way towards laser astrophysics experiments that one day will be able to assess the strongly and effectively magnetized regime that is the key to predictive experimental modeling of magnetized astrophysics.