Turbulent hydrodynamics experiments using a new plasma piston
- Lawrence Livermore National Laboratory, P.O. Box 808, Livermore, California 94550 (United States)
A new method for performing compressible hydrodynamic instability experiments using high-power lasers is presented. A plasma piston is created by supersonically heating a low-density carbon based foam with x-rays from a gold hohlraum heated to {approx}200 eV by a {approx}1 ns Nova laser pulse [E. M. Campbell et al., Laser Part. Beams 9, 209 (1991)]. The piston causes an almost shockless acceleration of a thin, higher-density payload consisting of a layer of gold, initially 1/2 {mu}m thick, supported on 10 {mu}m of solid plastic, at {approx}45 {mu}m/ns{sup 2}. The payload is also heated by hohlraum x-rays to in excess of 150 eV so that the Au layer expands to {approx}20 {mu}m prior to the onset of instability growth. The Atwood number between foam and Au is {approx}0.7. Rayleigh-Taylor instability, seeded by the random fibrous structure of the foam, causes a turbulent mixing region with a Reynolds number >10{sup 5} to develop between piston and Au. The macroscopic width of the mixing region was inferred from the change in Au layer width, which was recorded via time resolved x-radiography. The mix width thus inferred is demonstrated to depend on the magnitude of the initial foam seed. For a small initial seed, the bubble front in the turbulent mixing region is estimated indirectly to grow as {approx}0.036{+-}0.19 [{integral}{radical}(Ag)dt]{sup 2} which would imply for a constant acceleration 0.036{+-}0.019 Agt{sup 2}. More direct measurement techniques must be developed in larger scale experiments to remove potential complicating factors and reduce the error bar to a level that would permit the measurements to discriminate between various theories and models of turbulent mixing. (c) 2000 American Institute of Physics.
- OSTI ID:
- 20216075
- Journal Information:
- Physics of Plasmas, Vol. 7, Issue 5; Other Information: PBD: May 2000; ISSN 1070-664X
- Country of Publication:
- United States
- Language:
- English
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