What happens when additive manufacturing meets target fabrication engineering? An impossibly small, sub-millimeter scale cone that can be manufactured 10 times faster than before, enabling new target configurations for experiments at Lawrence Livermore National Laboratory (LLNL)'s National Ignition Facility (NIF).
"The compound parabolic concentrator is very challenging to work with," said LLNL mechanical designer Scott Vonhof. "At about 1.5 millimeters in size, it's smaller than the vacuum tips we used to manipulate parts and it has no flat surfaces. It was a problem in need of a solution."
Vonhof is part of a team of skilled experts that design, fabricate, assemble and test targets for NIF experiments. These tiny, precise assemblies contain dozens of components that channel laser energy to the fuel capsule and enable diagnostics to collect data. NIF can create conditions of extreme pressure and temperature to study high-energy-density (HED) physics.
"Target fabrication never sits still. We are constantly innovating to create targets that can deliver the experimental results the physicists want. We have many ideas that are waiting for the right technology to come along," said target fabrication engineer Soojin Stadermann.
One of those ideas was finding a better way to fabricate a compound parabolic concentrator (CPC), which channels an X-ray source to the fuel capsule during implosion to collect diagnostic data. The lengthy process involves diamond-turning a copper mandrel and coating it with gold and plastic, then machining the CPC again to form its final shape and leaching away the mandrel. Finally, the cone is mounted to a support structure.
The right technology enabling the idea was two-photon polymerization, or 2PP, an emerging additive manufacturing technique that uses a high-intensity, tightly-focused laser. The focal spot is smaller than one micron, so it can absorb two photons simultaneously.
"Previously, additive manufacturing couldn't achieve the required feature sizes," said Maxim Shusteff, the additive manufacturing deployment lead for target fabrication. "And the print area was too small, so we had to stitch parts together and those parts didn't meet the surface roughness requirements. 2PP opens a lot of design space for target fabrication."
The technique solved both issues. A CPC could be printed as a single assembly that didn't require gold coating, reducing production time from ten days to one day.
Fabricating the cone was only the first step. Any new component introduced into a NIF experiment, which produces critical national security data, must be meticulously characterized and tested to ensure it will not negatively impact experiments. With only about 300 NIF experiments conducted a year, new components are first tested at other lasers, like LLNL's Jupiter Laser Facility or the University of Rochester's Laboratory for Laser Energetics.
Targets must also be designed to prevent reflected laser light from traveling back into the beamlines and damaging optics. This requires strict tolerances for surface roughness and geometries that do not permit unwanted reflection.
In an April 2026 experiment, the 2PP-printed CPC was fielded as a component of a gold disc target, used to calibrate diagnostics. It performed as well as conventionally manufactured components. The new component was ready for prime time, and researchers had just the right experiment.
In support of ion fast ignition, a discovery science campaign studying how ions propagate through and interact with dense plasma needed a new target design that integrated the Advanced Radiographic Capability (ARC) ion source with the capsule using an indirect-drive design. About 8% of NIF's experimental time is dedicated to discovery science campaigns, which use the facility's extreme conditions to study HED physics in addition to its primary national-security mission.
"This would have been impossible without the new 2PP method," said Stadermann. "Directly attaching the CPC to the ion source was challenging because of the obscured location and stringent assembly tolerances."
For this experiment, target fabrication was able to design a new 2PP printed CPC that had the same inner shape as the one on a comparison shot a few months earlier, but its outer profile was different to make it easy to assemble inside a gold cone. By adding "guide rails" in the gold cone, the CPC could be slid into place accurately and tacked with glue.
2PP printing was also used for a second component: the re-entrant cone, which sits near the CPC cone. This part must be made with very high accuracy to prevent backscatter of laser light. This could have been accomplished with diamond turning, but the part's off-axis geometry would have made that very difficult.
The first experiment was successfully conducted in September 2026. The experimental team is analyzing the data, which will inform improvements in the target design for the next experiment in the campaign.
The engineers are also exploring other target fabrication applications for 2PP printing, including fuel capsules with lattice structures that could hold wetted foams, a new approach to forming capsule's the fuel layer.
"Now we have this geometric freedom that has really blown open the design possibilities," said Vonhof. "This component is just the beginning."
