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Proceedings Paper

High-speed imaging of Raleigh-Taylor instabilities in laser-driven plates
Author(s): Alan M. Frank; Calvin H. Gillespie; Wayne M. Trott
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Paper Abstract

We have previously reported our observations of the dynamic behavior of laser driven plates. Recent improvements and modification of the imaging techniques have identified and provided measurements of Raleigh-Taylor (R-T) instabilities that occur in these events. The microscope system in the LLNL Micro Detonics Facility, was converted to an epi- illuminated polarization configuration. A double pulse nanosecond illuminator and a second independently focusable frame camera were also added to the system. A laser driven plate, that is a dense solid driven by a laser heated, lower density plasma, is inherently R-T unstable. The characteristics and growth of the instability determine whether or not the plate remains intact. In earlier reports we correlated the surface patterning of thin plates with the fiber-optical transmission modes. In subsequent experiments we noted that the plasma burn through patterning in thin plates and the surface patterning of thicker plates did not correspond to the thin plate early time patterning. These observations led to the suspicion of R-T instability. A series of experiments correlating plate thickness and pattern spatial frequency has verified the instability. The plates are aluminum, deposited on the ends of optical fibers. They are launched by a YAG laser pulse traveling down the fiber. Plate velocities are several kilometers per second and characteristic dimensions of the instabilities are a few to tens of microns. Several techniques were used to examine the plates, the most successful being specularly reflecting polarization microscopy looking directly at the plate as it flies toward the camera. These images gave data on the spatial frequencies of the instabilities but could not give the amplitudes. To measure the amplitude of the instability a semi-transparent witness plate was placed a known distance from the plate. As above, the plate was observed using the polarization microscope but using the streak camera as the detector. Both the launch of the plate and its impact into the witness plate are observed on the streak record. Knowing the plate velocity function from earlier velocimetry measurements and observing the variations in the arrival time across the plate, the amplitude of the instability can be calculated.

Paper Details

Date Published: 28 May 1997
PDF: 9 pages
Proc. SPIE 2869, 22nd International Congress on High-Speed Photography and Photonics, (28 May 1997); doi: 10.1117/12.273355
Show Author Affiliations
Alan M. Frank, Lawrence Livermore National Lab. (United States)
Calvin H. Gillespie, Lawrence Livermore National Lab. (United States)
Wayne M. Trott, Sandia National Labs. (United States)

Published in SPIE Proceedings Vol. 2869:
22nd International Congress on High-Speed Photography and Photonics
Dennis L. Paisley; ALan M. Frank, Editor(s)

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