Experimental study of the hydrodynamics of high Mach number blast waves
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We have performed a series of experiments examining the properties of high Mach number blast waves. Preliminary experiments were conducted on the Janus laser at Lawrence Livermore National Laboratory while the majority of experiments were carried out on the Z-Beamlet laser at Sandia National Laboratories. We created blast waves in the laboratory by using 10 J- 1000 J laser pulses to illuminate millimeter scale solid targets immersed in gas. The experimental results can be grouped into three categories. Firstly, we confirmed the importance of line radiation on the evolution of the blast wave and that this importance increased with the atomic number of the gas used. This was determined through three measurements: Interferometric measurements of the size of the radiative precursor preceding the blast front, measurements of the blast wave trajectory, and measurements of the size of additional blast waves created by the radiation ablating material in the blast wave path. The second set of experiments examined the effect of the passage of a laser pulse on the subsequent evolution of the created blast wave. We find that the laser’s passage creates a warm channel of gas where a blast wave travels at higher velocity than it does through unperturbed gas. This creates a bulge-like feature on the blast wave surface. This effect is magnified in higher atomic number gases where multi-photon ionization is more prevalent, causing additional energy to be deposited in the gas. The final set of experiments studied the validity of theories forwarded to explain the dynamics of perturbations on astrophysical blast waves. These experiments consisted of a systematic scan of the decay rates of perturbations of known primary mode number induced on the surface of blast waves by means of a regularly spaced wire array. The amplitude of the induced perturbations relative to the radius of the blast wave was tracked and fit to a power law in time. Measurements were taken for a number of different mode numbers and background gasses and the results show qualitative agreement with previously published theories for the hydrodynamics of thin shell blast wave.