Abstract
Foam materials are starting to find application in laser-heated Hohlraums used to drive inertial confinement fusion implosions. Foams made using additive manufacturing (AM) techniques are now available and may have advantages over traditional chemical (aerogel) foams. Here, we present new experimental data on laser-heated AM foams. Samples of four different types of printed AM foams were heated using a single 527 nm laser beam at the Jupiter Laser Facility. The laser pulse was ∼180 J square pulse with an FWHM of 1.6 ns and a peak intensity of 3–4 × 1014 W/cm2. The foam densities ranged from 12 to 93 mg/cc (all supercritical for 527 nm light). We measured the backscattered light (power and spectrum), the transmitted light, side-on x-ray images, and the Ti K-shell emission that was used to infer the time-integrated temperature. The fraction of backscattered light was 6%–15% of the input laser energy. The pure carbon foam sample had less backscatter than a C8H9O3 foam of similar density, which was consistent with multi-fluid calculations that predicted less ion heating for the C8H9O3 foam. The level of backscatter and the thermal front speeds for the AM foams were similar to values measured for stochastic (aerogel) foams under similar conditions.
Highlights
In the indirect drive concept for inertial confinement fusion, laserheated cavities (“Hohlraums”) produce an x-ray radiation drive that implodes a deuterium-filled capsule
II, we describe the four types of foam samples that we made for this study
Experiments were performed at the Jupiter Laser Facility (JLF) at the Lawrence Livermore National Laboratory
Summary
In the indirect drive concept for inertial confinement fusion, laserheated cavities (“Hohlraums”) produce an x-ray radiation drive that implodes a deuterium-filled capsule. Foam liners have been proposed as a means to reduce Hohlraum wall motion and help control symmetry.[2,3,4] Here, densities of 10–100 mg/cc may be optimal, and so supercritical density foams are of interest. A number of simplified models have been developed to treat the foam structure without having to completely resolve it spatially These include 1D analytical models that account for the foam element expansion using similarity solutions.[6,7,8] Fully three dimensional calculations that treat the solid elements as pre-expanded “pixels” have been employed with success[9] because they are still expensive, their utility is primarily in testing and improving the simpler models. The foam densities ranged from 12 to 93 mg/cc and were all at or above critical density for green light
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