Richtmyer-Meshkov instability experiments on the Nova laser from nonlinear initial perturbations

We present the results from a series of experiments recently completed on the Nova laser studying the growth of the Richtmyer-Meshkov instability from an initially nonlinear perturbation. These are the first experimental measurements of the time-dependent mixing of materials at a shocked interface from a high-amplitude, short-wavelength perturbation in a high Mach number regime. The experiments were simulated using CALE, a two-dimensional arbitrary Lagrangian-Eulerian hydrodynamics code. The calculations correctly captured the measured growth of the mixing zone from the initial applied perturbation. The simulations also permitted consideration of nonideal effects (e.g. post-shock decompression) required to compare the results of calculation and experiment with theory. Both the experiment and calculations were found to be in good agreement with recent theories for the nonlinear evolution of the instability

Experimental study of the richtmyer-meshkov instability, including amplitude and wavelength variations

We report on results of an experimental study of the Richtmyer- Meshkov instability. The growth of the mixing region in the nonlinear regime is measured for a set of cases in which the amplitude and wavelength of the initial perturbation are varied systematically. The experiments are conducted on the Nova laser facility, and use a Nova hohlraum as a driver source to launch a high-Mach-number shock into a miniature shock tube attached to the hohlraum. The shock tube contains brominated plastic and low-density carbon foam as the two working fluids, with a micro-machined, triangular sawtooth interface between them serving as the initial perturbation. The sawtooth perturbation waveform is dominated by a single mode, and the perturbation amplitudes are chosen to expedite transition into the nonlinear phase of the instability. The shock, upon crossing the perturbation at the interface, instigates the Richtmyer- Meshkov instability. The resulting growth of the mixing region is diagnosed radiographically. Quantitative measurements of the temporal growth of the width of the mixing region are made for six different combinations of amplitude and wavelength, building upon previous results which employed a single amplitude/wavelength combination. Data from both experiment and supporting simulations suggest that the nonlinear growth of the mix width admits a logarithmic time dependence. The results also suggest that, properly normalized, the total mixing width grows in a nearly self-similar fashion, with a weak shape dependence

Mass distribution of hydrodynamic jets produced on the national ignition facility

The production of supersonic jets of material via the interaction of a strong shock wave with a spatially localized density perturbation is a common feature of inertial confinement fusion and astrophysics. The spatial structure and mass evolution of supersonic jets has previously been investigated in detail [J. M. Foster et. al, Phys. Plasmas 9, 2251 (2002) and B. E. Blue et. al, Phys. Plasmas 12, 056312 (2005)]. In this paper, the results from the first series of hydrodynamic experiments will be presented in which the mass distribution within the jet was quantified. In these experiments, two of the first four beams of NIF are used to drive a 40 Mbar shock wave into millimeter scale aluminum targets backed by 100 mg/cc carbon aerogel foam. The remaining beams are delayed in time and are used to provide a point-projection x-ray backlighter source for diagnosing the structure of the jet. Comparisons between data and simulations using several codes are presented