Browsing by Subject "Blast waves"
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Item Hydrodynamic instabilities of radiative blast waves(2013-12) Kim, In Tai; Ditmire, Todd R.We present the results from a series of experimental investigations into the hydrodynamic instabilities that occur in radiative blast waves. In particular, we examine the Vishniac instability in which the perturbation modes oscillate in time and, for certain mode numbers and polytropic index of the medium, can exhibit a growth in their amplitudes. Experiments were conducted on the GHOST laser laboratory in which a source of atomic clusters was irradiated by a 1J-2J, 115fs laser pulse to produce cylindrical blast waves. The thrust of this thesis falls into two categories. First, we analyze the effects radiative cooling has on the evolution of blast waves such as the lowering of the effective polytropic index and consequently the lowering of their deceleration parameter. Radiation from the blast wave surface results in a preheated ionization precursor in the upstream material and is indicated by a gradual decline in the electron density profile of the blast wave rather than a sharp jump. This mechanism, if strong enough, can also create a secondary shock wave to form ahead of the main blast wave. The second set of experiments investigates the temporal evolution of longitudinal perturbations induced on the blast waves by use of a transverse interferometric beam that modifies the cluster medium prior to the onset of the main pump beam. These perturbations are analyzed and compared to theory set forth in Vishniac's mechanism for oscillatory instabilities and their growth rate.Item Supernova in a bottle : experimental study of magnetic and radiative effects on scaled supernova remnant shocks(2016-12) Riley, Nathan James; Ditmire, Todd; Bengtson, Roger; Breizman, Boris; Keto, John; Shapiro, PaulRadiative shocks and blast waves are important in many astrophysical contexts, such as supernova remnant formation, cosmic ray production, and gamma ray bursts. Structure formation on radiative blast wave fronts in late-stage supernova remnants is expected to play a role in star formation via seeding of the Jeans instability. The origin of these structures is believed to be an instability described theoretically by Vishniac (ApJ 274, 152 (1983)), which has been subject to continued numerical and experimental investigation. Several laboratory experiments have been performed to study the stability of radiative blast waves in late-stage supernova remnants (PRL 66, 2738 (1991); PRL 87, 085004, (2001); PRL 95, 244503 (2005)), but have been limited by the lack of a realistic magnetic field within which the blast wave evolves. Magnetic fields play a significant role in the dynamics of astrophysical objects on multiple scales, such as shock collisionality, magnetic turbulence, and large-scale structure formation, but experimental efforts to investigate these effects on blast wave structure have been sparse. This work extends previous work in this area to cover the evolution of radiative blast waves in a dynamically significant magnetic field.