Description
Low-density polymer foams wicked with cryogenic liquid hydrogen are prime candidates to deliver nuclear fuel in inertial fusion power plants. These targets allow fast filling and uniform distribution of the fuel on the inside of a spherical capsule that is required for high-convergence implosions using laser-driven shock waves driven by ablation pressure. Their design requires high-precision equation of state data and understanding of instability hydrodynamics.
In April 2026, we completed the first cryogenic wetted foam experiment that visualizes shock wave propagation through foams that have been wicked with liquid deuterium at 25K. We utilized high-resolution X-ray imaging measurements at the Titan laser facility at Lawrence Livermore National Laboratory that delivered a 150-J, 600 fs short-pulse laser beam to drive a Cu K-alpha X-ray backlighter source at 8 keV. This setup provides X-ray phase-contrast images with 100 picosecond temporal resolution and 20-micron spatial resolution of the shock-compressed plasma driven by a second long-pulse laser beam at 450 J energies and smoothed with a 600-micron continuous phase plate. Our measurements provide new results on the shock speed and the shock uniformity for various types of foam structures revealing a path towards approaching the uniformity achieved in a pure deuterium liquid. The data further visualize the mixing of foam material with the liquid behind the shock, providing important benchmark data for hydrodynamic simulations of laser-driven fusion targets for inertial fusion energy.
These experiments provide the first measurements of the equation of state of wetted foams and comparisons with liquid deuterium. The results are of critically importance to design inertial fusion targets for public and private fusion efforts.
This work was funded by the DOE Office of Science, Fusion Energy Science under FWP100182. We acknowledge support from Department of Energy (DOE), Office of Science, Fusion Energy Sciences, under Award No. DE-SC 0024882: IFE-STAR was issued as SLAC FWP 101126. The work of XX, JV., SM, and RC was performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under Contract No. DE-AC52-07NA27344.