Passive freeze-out of the Richtmyer-Meshkov instability

Abstract

The Richtmyer-Meshkov instability (RMI) poses a major challenge in inertial confinement fusion (ICF) due to its role in mixing and performance degradation. We report the first experimental observation of passive freeze-out of RMI in a low-pressure surrogate regime; an instability stagnation effect induced without modifying the driving pressure pulse or the target surface geometry. Using additively manufactured sub-surface voids in a sinusoidal target, we convert a single shock into a sequence of weaker shocks that suppress instability growth upstream of the surface by over 70%. High-speed X-ray imaging and hydrodynamic simulations suggest that this suppression arises primarily from temporal shaping, with lesser contributions from spatial curvature and shock weakening. Our results demonstrate a driver-independent pathway for controlling shock-driven hydrodynamic instabilities relevant to ICF and other high energy density systems.

Figures (5)

• Figure 1: (a) Side-on and isometric view of the experimental setup showing the exploding copper foil, direction of the current flow, and sample geometry. (b) Initial conditions of the baseline (i) and instability mitigation (ii) sample geometry. Functions $L_i$ correspond to linear functions that approximate the optimal void geometry that is detailed in the Methods section.
• Figure 2: (a) X-ray radiographs of our baseline experiment showing shock compression of a sinusoidal surface. (b) Sequence of radiographs showing compression of the instability suppression sample. Green dashed lines highlight void structures while red lines show tracked interfaces.
• Figure 3: (a) Simulated pressure and density fields for the baseline scenario. (b) Corresponding fields from the instability suppression case, highlighting key dynamics. In each plot, the top half shows pressure, and the bottom half shows density. Pressure plots include white dashed contours indicating material interfaces or strong density gradients. Note: To highlight features, the pressure color bars vary between plots.
• Figure 4: (a) Jet tip position (red) and mean interface position (blue) vs. time for the baseline geometry. (b) Same as (a), for the suppression geometry (c) Integrated areal impulse delivered to the gelatine–air interface in the baseline case. (d) Same as (c), for the suppression case. The dashed vertical line indicates the time of interface inversion in all subplots.
• Figure 5: Mass modulation $\delta m / \left \langle \delta m_0 \right \rangle$ at three characteristic times, before shock-compression, shortly after, and at late time. Axis $y$ is perpendicular to direction of compression.