Single-mode and multimode Rayleigh–Taylor experiments on Nova

Abstract

Rayleigh–Taylor (RT) experiments have been conducted with planar CH(Br) foils accelerated by x-ray ablation from a shaped, low adiabat drive. The surface perturbations investigated consisted of single-mode, two-mode, and eight-mode sinusoids. The perturbation evolution begins during the shock transit phase, when perturbations show gradual growth due to Richtmyer–Meshkov-like dynamics. After shock breakout, the compressed foils accelerate and perturbation growth continues due to the Rayleigh–Taylor instability. Detailed comparisons with simulations indicate that in the linear Rayleigh–Taylor regime, the single-mode perturbations grow exponentially in time. In the nonlinear regime, the growth slows and the perturbation shape changes from sinusoidal to ‘‘bubble and spike’’ with the appearance of higher Fourier harmonics. In the multimode perturbations, the individual modes grow independently in the linear regime, but become coupled in the nonlinear regime. In addition to the higher harmonics of the individual modes, coupling leads to the appearance of ki±kj ‘‘beat’’ modes. This results in a redistribution of the perturbation into a broader Fourier spectrum causing a change of shape: bubbles become broader and flatter and spikes narrower, in agreement with simulations and multimode theory.

Progress toward the Laboratory Simulation of Young Supernova Remnants

“…The basic structure of the target was developed over a period of several years (Glendinning et al 1992 ;Kau †man et al 1994 ;Louis et al 1995 ;Peyser et al 1995 ;Remington et al 1995 ;Dimonte et al 1996). It has been used successfully for many hydrodynamic experiments.…”

Experiments in ICF, materials science, and astrophysics

“…In Fig. 1a, we show the measured planar ablation front RT dispersion curve from radiatively driven CH(Br) foils [1][2][3] vs. classical RT growth at an embedded, CH(Br)-Ti interface [4]. The ablation front RT growth vs. perturbation wavelength (lower, red curve) displays strong ablative stabilization, with the shortest wavelength ripples ( = 20 m) hardly growing at all.…”

“…The smooth curves represent simulations for the 2-mode superposed pattern, including nonlinear mode coupling (black) and for each wavelength simulated alone (gray curves). The difference represents the perturbation strength being shifted into the coupled terms, k 3 ± k 2 [3,7]. (d) Experiments and simulations of 2D vs. 3D single-mode perturbations growing at the ablation front of an x-ray driven CH(Br) foil.…”

Approaches to turbulence in high-energy-density experiments

“…The RT instability has been observed in HEDP systems, both at the ablation surface [26], where the action of the energy source causes hot, low-density plasma to accelerate cooler, denser plasma, and at an embedded interface [27], a case closer to the simple RT case. Other extensive work has also been undertaken and is ongoing in the context of inertial fusion research.…”