Turbulent hydrodynamics experiments using a new plasma piston

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 similar to 200 eV by a similar to 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 similar to 45 mu m/ns(2). The payload is also heated by hohlraum x-rays to in excess of 150 eV so that the Au layer expands to similar to 20 mu m prior to the onset of instability growth. The Atwood number between foam and Au is similar to 0.7. Rayleigh-Taylor instability, seeded by the random fibrous structure of the foam, causes a turbulent mixing region with a Reynolds number > 10(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 similar to 0.036 +/- 0.19 [integral root(Ag)dt](2) which would imply for a constant acceleration 0.036 +/- 0.019 Agt(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. [S1070-664X(00)95305-9].