Laboratory-astrophysics jet experiments at the omega laser facility

Abstract

Supersonic collimated jets are ubiquitous phenomena in astrophysics. Detailed information about astrophysical jets has traditionally come only from telescopes, theoretical analysis and numerical, resolution-limited, computer simulations which may not include all relevant physical processes. However, large high-energy-density facilities, such as the University of Rochester's Omega laser, now allow laboratory experiments on macroscopic volumes of plasma of relevance to astrophysics, and we use the laser to study the hydrodynamics of supersonic jets and bow shocks, with the aim of increasing understanding of astrophysical jets. We present results of an experiment in which a high-Mach-number, high-Reynolds-number millimeter-sized jet is formed by hohraum-driven radiation ablation of a 125-μm-thickness titanium foil mounted over a 700-μm-thickness titanium washer with a central, cylindrical hole. Some of the resulting shocked titanium expands, cools, and accelerates through the vacuum region (the hole in the washer) and then enters a cylinder of low-density foam as a jet. The jet is imaged using pinhole-apertured point-projection radiography. Such complex experimental data provide a challenge for both astrophysical and laser-plasma hydrocodes Although the high Reynolds number of the jet suggests that turbulence should develop, this behaviour cannot be reliably modelled by present, resolution-limited simulations. In addition to experimental results, we present data from 2D simulations which include the use of sub-grid-scale mix models.