Rayleigh-taylor instability growth experiments in a cylindrically convergent geometry Page: 3 of 9
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Rayleigh-Taylor Instability Growth Experiments...
Rayleigh-Taylor Instability Growth
Experiments in a Cylindrically
Convergent Geometry
S.T. Weir, E.A. Chandler, and B.T. Goodwin
Lawrence Livermore National Laboratory
University of California, P.O. Box 808
Livermore, CA 94550
Abstract: Convergent geometry Rayleigh-Taylor experiments have been performed with a
122-point detonation initiation system on cylinders having sinusoidal perturbations on the
outer surface ranging from mode-6 to mode-36. Experiments were performed with various
perturbation mode numbers, perturbation amplitudes, and ring accelerations. Feedthrough
perturbation growth on the inner surface was observed in several experiments, and in one
experiment the feedthrough perturbation underwent a phase inversion. These experimental
results were found to be in good agreement with linear, small-amplitude analysis of feedthrough
growth in an incompressible, cylindrically convergent geometry.
1. Introduction
The gelatin cylinder techniques has many features which make it a very attractive method
for studying Rayleigh-Taylor instabilities. Precise control can be exercised over the gelatin
strength, the driving pressure, and the initial perturbations. In addition, by using high-speed
framing cameras, it is possible to obtain high-resolution images of the entire implosion history
and to examine in detail all stages of the instability growth and cylinder collapse.
A number of interesting topics can be studied with this technique, including the rate of
turbulent mix development in a convergent geometry, the mode-mode coupling of RT unstable
modes in the weakly non-linear regime, and the feedthrough growth of perturbations on the
inner surface of the cylinder. This last topic is of special interest to members of the intertial
confinement fusion (ICF) community, since the feedthrough growth of instabilities is an impor-
tant ICF capsule design concern. In our most recent experiments, we have chosen to focus on
the observation and analysis of feedthrough growth in a cylindrically convergent geometry.
2. Experimental
In the previous set of experiments, we utilized up to 12 exploding bridge wires (EBWs) to
initiate the detonation of the oxygen-acetylene driving gas. However, with this small number
of initiation points, detonation front interactions between adjacent EBWs were significant, and
this seeded large localized perturbations on the cylinder. In our latest series of experiments,
we eliminated these large pressure-induced perturbations by using a 122-point EBW system.
With this new initiation system, we are able to systematically study the RT and feedthrough
growth rates for various initial perturbation wavelengths and amplitudes.
Our apparatus is essentially the same as that used in our previous experiments2, except
for the introduction of the 122-point EBW system. The gelatin rings were formed using water
with a 6% concentration of gelatin (Kind and Knox Company, 225 Bloom gelatin). The rings1
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Weir, S. T., LLNL. Rayleigh-taylor instability growth experiments in a cylindrically convergent geometry, article, June 11, 1997; (https://digital.library.unt.edu/ark:/67531/metadc619939/m1/3/: accessed April 24, 2024), University of North Texas Libraries, UNT Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.