Lawrence Livermore National Laboratory has achieved fusion ignition nine more times since it conducted the world’s first successful ignition experiment on Dec. 5, 2022 – setting records for fusion yield along the way.
(Download Image)Target Breakthrough Enabled Fusion Record at NIF
A variety of scientific and engineering breakthroughs – in lasers, optics, modeling, and diagnostics – have contributed to the series of successful fusion ignition experiments at Lawrence Livermore National Laboratory (LLNL)’s National Ignition Facility (NIF).
But perhaps no other single factor has been more important than the steady improvements in the quality of the tiny target capsules that hold the fusion fuel. In fact, a high-quality, custom-made high-density carbon (diamond) capsule was at the heart of the milestone NIF shot on April 7, 2025, that produced an unprecedented 8.6 megajoules (MJ) of fusion energy.
“The repeated achievement of fusion ignition at NIF is the outcome of an unparalleled degree of teamwork, innovation, and commitment to LLNL’s vital national security mission,” said Vincent Tang, Principal Associate Director of the NIF and Photon Science Directorate at LLNL. “This record result, enabled in part by a major innovation in target design, has sent a clear signal that the U.S. is expanding the frontier of fusion science and technology. These results continue to bolster NIF ignition capabilities we are applying to accelerate stockpile modernization”
“Success in target fabrication is shared very widely.”—Sal Baxamusa
The key to this record result was a process known as continuous gradient doping, in which a small amount of tungsten is gradually added to the vanishingly thin layers of synthetic diamond during capsule fabrication—a significant advancement in capsule design for inertial confinement fusion (ICF) research.
The April 2025 experiment achieved ignition—producing more fusion energy than the amount of laser energy delivered to the target—for the eighth time. In that shot, NIF’s lasers fired 2.08 MJ of energy into the target and produced a record fusion yield of 8.6 MJ, for a target gain greater than four.
Fusion ignition is a key element of NIF’s support for the National Nuclear Security Administration’s efforts to manage and modernize the nuclear stockpile. Record target gains also provide a physics basis for establishing fusion energy as a source of enduring baseload power with profound implications for economic security.
A ‘Dimmer Switch’
NIF’s indirect-drive ICF system relies on lasers heating the inside of a hohlraum, which emits x rays that implode the capsule inside and drive the fusion process. But hard “M-band” x rays can penetrate the capsule and preheat the fuel, reducing an implosion’s efficiency.
Traditionally, NIF capsules have used “step,” or uniform, dopant concentrations to absorb the unwanted x rays; but the presence of discrete layers of dopant introduces instabilities that also interfere with performance.
NIF’s diamond capsules are produced by a process called plasma-assisted chemical vapor deposition, in which tiny diamond crystals are painstakingly layered around a silicon carbide core over several days.
Continuous dopant technology, explains LLNL Target Fabrication engineer Sean Hayes, gradually ramps up the tungsten concentration from zero to its maximum (approximately 0.44 atomic percentage) over 10 microns of capsule thickness, then smoothly ramps it down again toward the outside of the shell. This process eliminates abrupt changes in dopant density.
“It’s the difference between having an off/on light switch and a dimmer switch,” says LLNL chemical engineer Sal Baxamusa, deputy program manager for Target Fabrication. “This is a way of ‘mitigating the mitigation.’ You put the dopant in to fix the x rays; then you grade the dopant so that you fix the density.”
The first full-scale test of continuous doping was conducted on Feb. 23, 2025, in an experiment that produced 5 MJ of fusion energy. According to Baxamusa, the innovation was made possible by years of incremental improvements in capsule quality, laser drive, and supporting technologies.
“If we had tried to use this trick as the cure for all our issues five years ago,” he says, “we would have been pretty disappointed.”
Manufacturing the advanced capsules requires a high degree of precision and collaboration. The Target Fabrication team, along with partners at Diamond Materials GmbH of Freiburg, Germany, and General Atomics in San Diego, succeeded in producing capsules with the exact dopant profile needed on the first attempt. Baxamusa credits every assembler, engineer, and scientist involved. “Success in target fabrication is shared very widely,” he says.
The process included high-throughput screening tools, such as the General Atomics 4Pi Integrated Metrology System, which enabled selection of the best capsules for deployment.
Integrating these new capsules into NIF experiments is not just a technical milestone but also a testament to the collaborative infrastructure built over years, Hayes says. “Target Fab has set up the infrastructure in a way where we could immediately pivot to this design and deliver it to support shots in the future.”
Mitigating Mix
According to LLNL physicist Dan Clark, deputy program lead for modeling in the ICF program and lead designer of the recent experiments, the primary benefit of continuous doping is its ability to reduce “mix”—the contamination of the fusion fuel by capsule material. The record April 2025 shot was only the second ignition experiment to use such a target.
“One of the big jumps in yield in the last few years was the step from 3.88 megajoules (on July 30, 2023) to the 8.6 megajoules that we saw” in the record shot, Clark says. “You get higher compression, you get cleaner fuel, and everything burns hotter and brighter.”
Matching the Models
The success of the continuous doping experiments was not unexpected. By modeling dopant introduction in computational simulations, Clark and his team had shown how mix could lead to substantial implosion degradation.
“Over the last couple of years,” he says, “we’ve spent a lot of effort and energy in very high-resolution modeling of our implosions. It became apparent that the jump from the undoped inner part of the HDC ablator to the doped HDC ablator was very unstable. A lot of mix starts right at that interface.”
The simulations suggested that continuous doping could reduce hydrodynamic instabilities and mix. That in turn had the potential to significantly increase implosion compression and fusion yield.
Clark praised the Target Fabrication team for producing the “magic targets” that met the demanding specifications suggested by the models. “They worked for a couple of years to get it right,” he says, “and finally got something that was pretty close to what the modeling said would do what we wanted it to do.”
Looking ahead, experiments at NIF will continue to evaluate how these new target designs can unlock higher fusion yields, opening new applications for national security research.
More Information:
“Big Ideas Lab Podcast Zooms in on Tiny Targets,” NIF & Photon Science News, March 10, 2026
“The Future of Ignition,” Science & Technology Review, July/August 2025
“Cracking the Fusion Codes,” Science & Technology Review, July/August 2025
“Target Evolution Is a Key to NIF’s Continued Success,” NIF & Photon Science News, April 20, 2023
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