Speaker
Jose Luis Milovich
Description
See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P1.2012.pdf
Simulation Studies of the Interaction of Laser Radiation with Additively
Manufactured Foams*
J.L. Milovich1, O. S. Jones1, S. Wilks1, B. Winjum2, S. Langer1, L. Zepeda-Ruiz1, J.
Biener1 and M. Stadermann1
1
Lawrence Livermore National Laboratory, Livermore CA 94551
2
University of California, Los Angeles CA 90095
In indirect drive inertial confinement fusion, a high-Z enclosure (or “hohlraum”) surrounds a low-
Z capsule containing DT fuel. Laser beams irradiate the interior of the hohlraum, which creates an
x-ray radiation bath compressing the fuel to ignition conditions. The irradiated hohlraum wall
motion leads to dynamic drive symmetry swings that degrade the implosion. To mitigate this wall
motion, hohlraums are typically filled with helium gas. A side effect is that for moderately high
fill densities (> 0.6 mg/cc) experiments have shown a substantial amount of backscattered light,
while for low densities the wall motion increases. Modern hohlraum designs are beginning to use
foams in two ways. First, high-Z metallic foams may be effective in reducing wall motion without
compromising capsule drive. Second, low-density mid-Z foams can be used as a substitute for
higher density gas fills with the added advantage of possibly using embedded dopants to
potentially mitigate backscatter losses. The interaction of laser radiation with foams of various
porosity sizes and average densities has been the subject of several numerical and experimental
studies [1]. In all cases, modelling foams using standard radiation-hydrodynamics codes have
shown considerably disagreement with experimental measurements. These discrepancies have
been attributed in large part to the inability of rad-hydro codes to faithfully represent the statistical
nature of foams (solid ligaments of full density material and large vacuum pore sizes ~ 1-10 µm),
typically modelled as a uniform gas of equivalent density. This deficiency may benefit from
modern computer architectures (many processors) and newly developed equation of state models.
In this work we use the rad-hydro code HYDRA and a simple foam statistical representation to
show that this configuration goes a long way to bridge the modelling disparities. Further ease on
modelling requirements can be leveraged from the use of structured foams. Recent developments
in additive manufacturing (AM) allow for the fabrication of structured foams of specified average
density. Currently, strands with ~ 500 nm diameter and pore sizes as small as several microns can
be laid down in a structured pattern, but the technology is quickly evolving. We use HYDRA to
survey a variety of AM foam configurations to find an optimal design for hohlraum experiments.
[1] S.Y. Gus’kov et al., Quantum Electron., 24 696 (1997); S.Y. Gus’kov et al., Phys. of Plasmas 18, 103114
(2011); Ph. Nicolai et al., Phys. of Plasmas 19, 113105 (2012).
* Work performed under the auspices of U.S. Department of Energy by LLNL under Contract DE-AC52-07NA27344
and supported by LDRD-17-ERD-118
