Ablation front rayleigh taylor dispersion curve in indirect drive
The Rayleigh-Taylor (RT) instability, which occurs when a lower-density fluid accelerates a higher-density layer, is common in nature. At an ablation front a sharp reduction in the growth rate of the instability at short wave-lengths can occur, in marked contrast to the classical case where growth rates are highest at the shortest wavelengths. Theoretical and numerical investigations of the ablative RT instability are numerous and differ considerably on the level of stabilization expected. We present here the results of a series of laser experiments designed to probe the roll-over and cutoff region of the ablation-front RT dispersion curve in indirect drive. Aluminum foils with imposed sinusoidal perturbations ranging in wavelength from 10 to 70 pm were ablatively accelerated with a radiation drive generated in a gold cylindrical hohlraum. A strong shock wave compresses the package followed by an {approx}2 ns period of roughly constant acceleration and the experiment is diagnosed via face-on radiography. Perturbations with wavelengths {ge} 20 {micro}m experienced substantial growth during the acceleration phase while shorter wavelengths showed a sharp drop off in overall growth. These experimental results compared favorably to calculations with a 2-D radiation-hydrodynamics code, however, the growth is significantly affected by the rippled shock launched by the drive. We performed numerical simulations to elucidate the influence of the rippled shock wave on the eventual growth of the perturbations, allowing comparisons to the analytic model developed by Betti et al. This combination of experiments, simulations and analytic modeling illustrates the qualitative simplicity yet quantitative complexity of the compressible RT instability. We have measured the Rayleigh-Taylor (RT) dispersion curve for a radiatively-driven sample in a series of experiments on the Nova laser facility. Planar aluminum foils were ablatively-accelerated and the subsequent perturbation growth was diagnosed via x-ray radiography. These measurements unambiguously map out the linear regime dispersion curve, including the observation of stabilization at short wavelengths. The data are compared favorably to two-dimensional simulations. Due to the influence of the rippled shock transit phase of the experiment, direct comparison to the ablation front RT theory of R. Betti was difficult. Instead, a numerical ''experiment'' was constructed that minimized the influence of the shock and this was compared to the Betti model showing quite good agreement.
- Research Organization:
- Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States)
- Sponsoring Organization:
- US Department of Energy (US)
- DOE Contract Number:
- W-7405-ENG-48
- OSTI ID:
- 15006505
- Report Number(s):
- UCRL-JC-139581; TRN: US0400835
- Resource Relation:
- Journal Volume: 8; Journal Issue: 5; Conference: 42nd Annual Meeting of the APS Division of Plasma Physics, Quebec City (CA), 10/23/2000--10/27/2000; Other Information: PBD: 17 Nov 2000
- Country of Publication:
- United States
- Language:
- English
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