For the last six decades, LLNL researchers and their colleagues have been working to achieve one of the most challenging goals in all of science and a primary objective of NIF: fusion ignition. The goal was reached on Dec. 5, 2022, thanks to a wide-ranging international partnership and sustained efforts by every aspect of NIF and LLNL operations—the laser, targets, optics, diagnostics, modeling and simulations, and the people who make it all possible (see “Keys to Our Success”).
Achieving ignition—producing more fusion energy than the amount of laser energy delivered to the NIF target—provides new opportunities for stockpile stewardship applications; NIF’s recreation of extreme environments allows scientists to study the behavior of materials under weapons-relevant conditions that were previously impossible to achieve in a laboratory setting. The 2022 achievement is not only vital for maintaining the effectiveness and safety of the U.S. nuclear arsenal but also enhances the prospects for an inertial fusion energy future.
In “indirect drive” inertial confinement fusion (ICF) experiments on NIF, up to 192 laser beams are fired into a centimeter-sized hollow cylinder called a hohlraum. This generates a “bath” of soft x rays that ablate, or blow off, the surface of a peppercorn-sized capsule suspended in the hohlraum.
The result is a rocket-like implosion that compresses and heats partially frozen hydrogen isotopes inside the capsule to conditions of pressure and temperature found only in the cores of stars and giant planets and in exploding nuclear weapons. The speed of the implosion—more than 400 kilometers per second—allows the fusion reactions to take place before the fuel can disassemble; the fuel is trapped by its own inertia (hence the term inertial confinement fusion).
What Is Fusion?
Fusion describes what happens when the nuclei of light atoms such as hydrogen overcome the repulsive electrostatic force that keeps them apart. When the nuclei get close enough, the force that binds protons and neutrons together, the strong force, takes over and pulls the nuclei even closer together so they “fuse” into a new, heavier helium nucleus with two neutrons and two protons.
The helium nucleus, also known as an alpha particle, has a slightly smaller mass than the sum of the masses of the two hydrogen nuclei, and the difference in mass is released as energy according to Albert Einstein’s famous formula E=mc2. The energy is released in the form of the alpha particles, high-energy neutrons, and other forms of energy such as electromagnetic radiation.
Nuclear fusion is different from nuclear fission, where the nuclei of heavy elements like uranium are split, forming two lighter elements—the process used in today’s nuclear power plants. In both nuclear reactions, the elements themselves change and become new elements—and in the process, a small amount of mass is converted to a large amount of energy.
What Is Ignition?
Fusion ignition occurs when the heating power from alpha particles produced by fusion reactions in the hot spot at the center of the target capsule overcomes the cooling effects of x-ray losses, electron conduction, and implosion expansion. When enough alpha particles are “stopped,” or absorbed, in the high-density fuel layer, a process known as alpha heating, a burn wave of fusion reactions propagates into the cold fuel surrounding the hot spot. When the energy deposition by the alpha particles contributes more than 50 percent of the heating of the fuel, a self-sustaining feedback loop known as a “burning plasma” results in an explosive amplification of energy output.
The NIF experiment on Dec. 5, 2022, far surpassed the ignition threshold by producing 3.15 megajoules (MJ) of fusion energy output from 2.05 MJ of laser energy delivered to the target.
LLNL researchers have since continued to repeat the ignition achievement with increasing yield and target gain. Some of the major milestones have included:
- On Oct. 30, 2023, NIF set a new record for laser energy, firing 2.2 MJ of energy for the first time on an ignition target. This experiment resulted in 3.4 MJ of fusion energy yield.
- An experiment on Feb 12, 2024, produced an estimated 5.2 MJ—more than doubling the input energy of 2.2 MJ.
- An experiment on April 7, 2025, set new records for both energy yield and target gain. NIF achieved a yield of 8.6 MJ with a measurement uncertainty of +/- 0.45 MJ. NIF’s lasers delivered 2.08 MJ of energy to the target in a 456-terawatt peak power pulse, producing a target gain of 4.13.
- On June 22, 2025, a Los Alamos National Laboratory-led team working with LLNL achieved ignition using NIF. The team conducted an experiment that generated a yield of 2.4 MJ of energy, with a measurement uncertainty of +/- 0.09 MJ and created a self-sustaining feedback loop called a burning plasma.
- On Oct. 1, 2025, LLNL conducted an experiment at NIF that generated a yield of 3.5 MJ, with a measurement uncertainty of +/- 0.17& MJ. NIF's lasers delivered 2.065 MJ of laser energy to the target, producing a target gain of 1.74. This experiment assessed the ability of U.S. nuclear weapons to survive encounters with adversary missile defenses and reach their targets, a demonstration of a new capability to analyze nuclear materials under extreme conditions to advance stockpile modernization.
Additional experiments using higher laser energies and producing even higher energy yields are expected, further demonstrating that NIF can repeatedly conduct fusion experiments at multi-megajoule levels of energy output.
Achieving ignition was an unprecedented, game-changing breakthrough that advances the science of ensuring the reliability of the nation’s nuclear stockpile (see “NIF and Stockpile Stewardship”) as well as the potential use of fusion as a safe, clean, and virtually unlimited energy source.
Gaining New Understanding
While reaching ignition on NIF proved more challenging than first expected, researchers gained new understanding of the process with every experiment. For example, they learned important lessons about the initial limitations of their simulations and used that knowledge to continually improve both the models and implosion performance.
In particular, the advent of high-resolution 3D modeling and simulations contributed to a better understanding of the perturbation sources—including such “engineering features” as the thin membranes that suspend the target capsule inside the hohlraum and the fill tubes used to inject fuel into the capsule—that interfere with implosion performance. Other factors inhibiting energy yield are laser-plasma and hydrodynamic instabilities, asymmetries in the hohlraum x-ray flux that drives the implosion, and the mixing of capsule material with the fuel.
The addition of new and enhanced diagnostics, such as multiple line-of-sight neutron detectors, also led to improved target performance. The ability of new high-performance supercomputers and powerful “deep learning” techniques to process, analyze, and simulate the mountain of data produced by these diagnostics in 3D over a broad range of perturbation sources—capsule surface imperfections, engineering features, drive asymmetries—significantly improved the ability of simulations to match, and even predict, experimental results (see “Pursuing Ignition: A Decade of Progress”).
Setting Energy Records
Since the first NIF laser shots, scientists have set records for neutron yield and the amount of energy generated. Neutron yields have grown exponentially since NIF experiments began; more energy is being coupled to the target capsule; implosion velocities have increased; and the pressures in the center of the implosion are many times higher. The result has been a steady increase in energy yield that culminated with the NIF experiment that produced a yield of more than 8 MJ, more than six times the record yield of 1.35 MJ set in 2021 (see “Threshold of Ignition”).
“Nature does not give up her secrets easily.”—NIF Senior Scientist John Lindl
NIF also made history in May, 2018, when it fired a record 2.15 MJ of ultraviolet energy to the Target Chamber—a 15 percent improvement over NIF’s design specification of 1.8 MJ and more than 10 percent higher than NIF’s previous 1.9 MJ energy record set in March, 2012. Subsequent experiments have further boosted the laser's energy to a new record high of 2.2 MJ.
Researchers strive to further improve NIF’s performance by coupling even more laser energy to the capsule while maintaining symmetry control and minimizing fuel contamination from target capsule material, or “mix.” We also are pursuing strategies like novel hohlraum designs; larger and thicker capsules; and new methods for finishing, mounting, and filling capsules.
We owe our progress to the decades of remarkable work by previous generations of LLNL scientists and engineers who advanced the field of high energy density and ICF science to where it is today. A new generation of LLNL researchers are carrying on this tradition of excellence.
More Information:
“The Age of Ignition: Inside LLNL's Fusion Breakthrough,” a NIF & Photon Science News Special Report
“Beyond Ignition,” Science & Technology Review, July/August 2025
“LLNL Conducts Milestone Nuclear Survivability Experiment at NIF,” NIF & Photon Science News, December 1, 2025
“New Book Documents Optics Innovations That Were Integral to Ignition,” NIF & Photon Science News, September 9, 2025
“LLNL Researchers Employed an AI-Driven Model to Predict Fusion Ignition Shot,” NIF & Photon Science News, August 29, 2025
“The Fire That Powers the Universe: Harnessing Inertial Fusion Energy,” NIF & Photon Science News, December 1, 2024
“Diagnostics Explored the ‘Unknowns’ in NIF Ignition Experiments,” NIF & Photon Science News, September 25, 2024
“Automated Target Measurements Contribute to LLNL's Ignition Success,” NIF & Photon Science News, September 5, 2024
“Ignition Gives U.S. ‘Unique Opportunity’ to Lead World’s IFE Research,” NIF & Photon Science News, February 2, 2023
