The Shock/Shear platform for planar radiation-hydrodynamics experiments on the National Ignition Facility

Abstract

An indirectly-driven shock tube experiment fielded on the National Ignition Facility (NIF) was used to create a high-energy-density hydrodynamics platform at unprecedented scale. Scaling up a shear-induced mixing experiment previously fielded at OMEGA, the NIF shear platform drives 130 μm/ns shocks into a CH foam-filled shock tube (∼ 60 mg/cc) with interior dimensions of 1.5 mm diameter and 5 mm length. The pulse-shaping capabilities of the NIF are used to extend the drive for >10 ns, and the large interior tube volumes are used to isolate physics-altering edge effects from the region of interest. The scaling of the experiment to the NIF allows for considerable improvement in maximum driving time of hydrodynamics, in fidelity of physics under examination, and in diagnostic clarity. Details of the experimental platform and post-shot simulations used in the analysis of the platform-qualifying data are presented. Hydrodynamic scaling is used to compare shear data from OMEGA with that from NIF, suggesting a possible change in the dimensionality of the instability at late times from one platform to the other.

Late-Time Mixing Sensitivity to Initial Broadband Surface Roughness in High-Energy-Density Shear Layers

“…The overall mixing layer Reynolds number, calculated conventionally at late times using the overall dynamic mixing-layer width (∼300 μm) as the scale length [11,35], remains over 10 6 , and is expected to be post-transition in both cases. Reference [8] has details about how the tracer mix layer evolves on the surface and in the bulk under KH shear, and can be thought of as a half-layer for the energy and mix analysis [25].…”

“…volume of this platform is large enough that edge effects and drive transients do not have time to propagate inward to interfere with the physics over the time scale over which the data are collected [8]. Varying the initial roughness on otherwise identical aluminum foils, we have observed a change in the behavior of the mixing layer as it is forced from typical Kelvin-Helmholtz (KH) coherent features [6,7], corresponding to an initial Reynolds number of ∼10 3 , to an increasingly turbulent behavior with highly stochastic features at an initial Reynolds number of > 10 5 .…”

“…However, KH systems driven single sidedly by impulsive decaying shock waves have been studied previously and typically in only one of the two mixing materials or in the presence of imposed initial sinusoidal seed perturbations [17][18][19][20][21][22][23]. This platform [8,24,25] uses a 10 ns indirect drive from two sides to support the shocks during the experiment.…”

“…However, these experiments did not last long enough for a full determination of the late-time asymptotic behavior of the system. Thus, a similar experimental platform was developed for the NIF [8,24,25] using indirectly (soft x-ray) driven ablators. The platform is shown in Fig.…”

Evolution of surface structure in laser-preheated perturbed materials

“…This is not necessarily valid [36] and a more thorough understanding of how initial conditions evolve is important in correctly interpreting the results of these experiments. For instance, the work presented here is part of a larger experimental effort investigating shear instability in a geometry involving counterpropagating flows [37,38]. The flow consists of two shocks in a low-density CH foam, driven in opposite directions by laser ablation, on either side of an aluminum collimating layer.…”