Radiative Reverse Shock Experiments in High-energy-density Plasmas.

Abstract

This thesis presents the development of a new high-energy-density laboratory astrophysics (HEDLA) experimental platform that explores radiative reverse shock waves. In the context of this work, a reverse shock is a shock wave that develops when a freely flowing, supersonic plasma is impeded. Obtaining a radiative reverse shock in the laboratory requires a sufficiently fast flow (> 60 km/s) within a material whose opacity is large enough to produce energetically significant emission from experimentally achievable layers. Data show that when these conditions are met, the post-shock material evolution is quite different than in an analogous purely hydrodynamic system. In the case where a plasma flow collides orthogonal to a surface, radiative losses cause the collapse of shocked material to high densities, such that the compression across the shock is >> 4. Additionally, when a stream impacts a surface at an angle, an oblique shock will divert the material moving through it, creating a supersonic shear flow that may become unstable. This work is motivated by the ambiguities that surround reverse radiative shocks and their contribution to the evolving dynamics of the cataclysmic variable in which they occur. Cataclysmic variables are close binary star systems containing a white dwarf (WD) which accretes matter from its late-type main sequence companion star. They can be classified under two main categories, non-magnetic and magnetic. In the process of accretion, both types involve strongly radiating shocks that provide the main source of radiation in the binary systems. In the case of the non-magnetic CV, mass onto an accretion disk produces this ‘hot spot’, where the infalling supersonic flow obliquely strikes the rotating accretion disk. Astrophysical simulations of this collision region show various outcomes as a function of the code's treatment of radiative cooling [1]. Ultimately, HEDLA experiments aim to bridge the gap between theoretical models and observations, and the design of laboratory experiments presented in this text suggest that correlations may be made to the CV system. [1] P.J. Armitage and M. Livio. Hydrodynamics of the Stream-Disk Impact in Interacting Binaries. Astrophysical Journal, 493:898, January 1998.PhDApplied PhysicsUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/102293/1/krauland_1.pd