Numerical simulation of supernova-relevant laser-driven hydro experiments on OMEGA

Abstract

In ongoing experiments performed on the OMEGA laser [J. M. Soures et al., Phys. Plasmas 5, 2108 (1996)] at the University of Rochester Laboratory for Laser Energetics, nanosecond laser pulses are used to drive strong blast waves into two-layer targets. Perturbations on the interface between the two materials are unstable to the Richtmyer–Meshkov instability as a result of shock transit and the Rayleigh–Taylor instability during the deceleration-phase behind the shock front. These experiments are designed to produce a strongly shocked interface whose evolution is a scaled version of the unstable hydrogen–helium interface in core-collapse supernovae such as SN 1987A. The ultimate goal of this research is to develop an understanding of the effect of hydrodynamic instabilities and the resulting transition to turbulence on supernovae observables that remain as yet unexplained. The authors are, at present, particularly interested in the development of the Rayleigh–Taylor instability through the late nonlinear stage, the transition to turbulence, and the subsequent transport of material within the turbulent region. In this paper, the results of numerical simulations of two-dimensional (2D) single and multimode experiments are presented. These simulations are run using the 2D Arbitrary Lagrangian Eulerian radiation hydrodynamics code CALE [R. T. Barton, Numerical Astrophysics (Jones and Bartlett, Boston, 1985)]. The simulation results are shown to compare well with experimental radiography. A buoyancy-drag model captures the behavior of the single-mode interface, but gives only partial agreement in the multimode cases. The Richtmyer–Meshkov and target decompression contributions to the perturbation growth are both estimated and shown to be significant. Significant dependence of the simulation results on the material equation of state is demonstrated, and the prospect of continuing the experiments to conclusively demonstrate the transition to turbulence is discussed.

Nonlinear mixing behavior of the three-dimensional Rayleigh–Taylor instability at a decelerating interface

“…This rapid growth of the spikes in the data leads one to ask whether or not their behavior is consistent with the buoyancy-drag models often used to describe RT turbulence, and fairly successful at describing the mix-layer growth for two-dimensional perturbations. 15 It makes sense here to examine the growth of the spikes as we can determine this more accurately because expansion is not an essential aspect. In addition, one might hope the model would be more accurate for the spikes, as during their evolution there is little compression and the theory is formally for incompressible fluids.…”

“…In recent work with decelerating-interface experiments, buoyancy-drag models have proven successful, after adjusting for compressibility effects, in explaining observations with single-mode perturbations and 2D simulations have proven able to reproduce, on the whole, observations with 2D multimode perturbations. 15 In addition, simulations of complex astrophysical phenomena remain largely 2D.…”

Approaches to turbulence in high-energy-density experiments

“…Note also that in this case, there are no indications of rollups at the spike tips. Experiments using 2D initial perturbations, having a comparable value of R, do observe definite rollups at the tips but also do not show an onset of turbulence [29], in contrast with results from low-energy-density, low-Atwood-number experiments [22].…”

“…Other extensive work has also been undertaken and is ongoing in the context of inertial fusion research. In addition, RT growth has been studied when a blast wave first shocks and then decelerates an embedded interface, in experiments motivated by supernova explosion dynamics [28][29][30][31]. In these cases, there is an initial RM response followed by a longer period of RT growth.…”

Concept Development for Astrophysically Relevant Turbulence on NIF

“…Therefore, we mark this time (40 ns) as the experimental time scale. Note that the impulsive positive acceleration of the interface by the blast wave front induce some Richtmyer-Meshkov instability (RM) growth [17,22], which can be viewed as adding to the total growth or as establishing an initial condition for RT with a significant velocity perturbation [18,7]. However, the RM contribution is expected to be small comparing to the RT growth, due to the fast decay in the induced velocity behind the blast wave front.…”