UCRL-JC-131851
PREPRINT
Developing Solid State Experiments
on the Nova Laser
D. H. Kalantar, B. A. Remington, E. A. Chandler,
J. D. Colvin, D. M. Gold, K. 0. Mikaelian,
S. V. Weber, L. G. Wiley, J. S. Wark,
A. Loveridge, B. H. Failor, A. Hatter,
M. A. Meyers, and G. Ravichandran
This paper was prepared for submittal to the
Second International Workshop on Laboratory
Astrophysics with Intense Lasers
Tucson, Arizona
March 19-21, 1998
August 6,1999
This is a preprint of a paper intended for publication in a journal or proceedings.
Since changes may be made before publication, this preprint is made available with
the understanding that it will not be cited or reproduced without the permission of the
author.
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Developing solid state experiments on the Nova Laser”
D. H. Kalantar, B. A. Remington, E. A. Chandler, J. D. Colvin,
D. M. Gold, K. 0. Mikaelian, S. V. Weber, L. G. Wiley
Lawreme Livermore National Laboratory
J. S. Wark, A. Loveridge
University of Oxford
B. H. Failor, A. Hauer
Los Alamos National Laboratory
M. A. Meyers
University of California, San Diego
G. Ravichandran
California Institute of Technology
An x-ray drive has been developed to shock compress metal foils in the solid
state using an internally shielded hohlraum with a high contrast shaped pulse from
the Nova laser. The drive has been characterized and hydrodynamics experiments
designed to study growth of the Rayleigh-Taylor (RT) instability in Cu foils at 3 Mbar
peak pressures in the plastic flow regime have been started. Pre-imposed
modulations with an initial wavelength of 20-50 pm, and amplitudes of 1.0-2.5 pm
show growth consistent with simulations.
In the Nova experiments, the fluid and
solid states are expected to behave similarly for Cu. An analytic stability analysis is
used to motivate an experimental design with an Al foil where the effects of
material strength on the RT growth are significantly enhanced. The conditions
reached in the metal foils at peak compression are similar to those predicted at the
core of the earth.
Introduction
In a classical fluid model, when a light fluid accelerates a heavier fluid, the
interface is Rayleigh-Taylor (RT) unstable. As a result, any mass modulation at the
embedded material interface is unstable, and can grow when accelerated. However,
when the material is in the solid state, the strength of the material can counter the
effect of the RT instability. The parameters that define whether a material is stable
or unstable to instability growth in the solid state depend on the wavelength and
amplitude of the modulation, the acceleration, foil thickness, and material
properties, such as yield stress, shear modulus, and the acceleration history.
Solid state instability growth will occur in the plastic flow regime. Plastic
behavior is described by a semi-empirical constitutive model [Steinberg, D. J., 19801
that has been developed for phenomena that occur at strain rates <lo5 s-l. This
model is an elastic-perfectly plastic model. When a stress is applied to a sample, it
responds elastically
up
to the point where the stress exceeds the yield stress. At that
point, it yields to plastic flow.
In fact, the material has a lattice structure not accounted for in such an
empirical description.
When the solid undergoes deformation at high pressure,
stresses that occur at a lattice level result in the generation and subsequent
propagation of d’ 1 1s ocations [Chhabildas, L. C., 1979; Lebedev, A. I., 19931. It is the
rearrangement of the lattice structure by transport of these dislocations that
constitute plastic material flow. Such plastic flow has been modeled either
microscopically by the theory of lattice dislocations, or macroscopically by an
effective lattice viscosity [Chhabildas, L. C., 19791. The best approach to describe the