When Lawrence Livermore National Laboratory (LLNL) achieved fusion ignition at the National Ignition Facility (NIF) in December 2022, the world's attention turned to the prospect of how that breakthrough experiment - designed to secure the nation's nuclear weapons stockpile - might also pave the way for virtually limitless, safe and carbon-free fusion energy.
Advanced 3D printing offers one potential solution to bridging the science and technology gaps presented by current efforts to make inertial fusion energy (IFE) power plants a reality.
"Now that we have achieved and repeated fusion ignition," said Tammy Ma, lead for LLNL's inertial fusion energy institutional initiative, "the Lab is rapidly applying our decades of know-how into solving the core physics and engineering challenges that come with the monumental task of building the fusion ecosystem necessary for a laser fusion power plant. The mass production of ignition-grade targets is one of these, and cutting-edge 3D printing could help get us there."
Today's ignition targets are nearly perfect spheres of hollow diamond encasing the deuterium and tritium (DT) fusion fuel, suspended in a golden cylinder called a hohlraum. When exposed to intense laser energy, these hydrogen isotopes fuse and can produce more energy than was needed to start the reaction.
The need for perfection is such that, if a NIF capsule were enlarged to the size of the Earth, an imperfection higher than the Hollywood sign in Los Angeles would be disqualifying.
While NIF targets take months to manufacture, a functioning fusion energy power plant will require nearly one million targets a day, igniting at a rate of ten times a second. The physical reaction would be similar to ignition at NIF, but the production of targets requires a fundamentally new approach that can work at scale.
To explore new approaches, a Laboratory Directed Research and Development (LDRD) effort is developing a 3D-printed target capability at NIF.
This project, led by James Oakdale and Xiaoxing Xia, is advancing additive manufacturing by constructing a workflow to design, fabricate, characterize and field fully 3D-printed fuel capsules. It is also developing a first-of-its-kind dual-wavelength, two-photon polymerization (DW-2PP) approach to push the current limits of additive manufacturing to meet the stringent engineering demands of ignition targets.
"We are focusing on a specific type of wetted-foam capsule, in which liquid DT can be wicked into a uniform foam layer on the inside of the spherical capsule by capillary action," said Xia, co-principal investigator and a staff scientist in the Lab's Materials Engineering Division. "The current DT ice layering process takes up to a week to complete with extreme meticulousness. It's possible that 3D printing is the only tool for this kind of complex geometry at scale."
In addition, the new DW-2PP approach will further enhance printing resolution and enable multi-material printing. If successful, this project will address critical bottlenecks towards 3D-printing ignition capsules in their entirety.
"Our DW-2PP printer uses two light sources with different wavelengths to selectively print different materials with sub-micron resolution," said co-principal investigator Oakdale, a staff scientist in the Lab's Materials Science Division. "This novel capability gives us exquisite control over the spatial chemistry and densities within both the capsule and inner foam material, which allows us to respond quickly to bespoke or one-off capsule designs."
The work is already showing promise, with 3D-printed targets successfully used during two NIF experiments in 2024 and more expected in the year ahead.
Whether this technology turns out to be a fusion energy solution remains to be seen. The use of 3D printing in NIF experiments has already produced vital data in support of the nation's Stockpile Stewardship Program, which makes use of singular facilities like NIF to understand nuclear weapons without underground testing.
"Unlocking fusion is a strategic asset for U.S. competitiveness," said Jeff Wisoff, principal associate director for LLNL's NIF & Photon Science Directorate. "It's imperative that we invest in fundamental science and technology to build on the historic achievement of fusion ignition. Doing so secures the stockpile as well as lays the groundwork for a fusion energy revolution."
- Thomas Lynch
