An experiment at Lawrence Livermore National Laboratory’s (LLNL’s) National Ignition Facility (NIF) appears to have approached fusion ignition as it recreated the extreme temperatures and pressures at the heart of the sun for a tiny fraction of a second. The momentous step has fueled new optimism for fusion energy.
The experiment on Aug. 8 “was enabled by focusing laser light from NIF—the size of three football fields—onto a target the size of a BB that produces a hot-spot the diameter of a human hair, generating more than 10 quadrillion watts of fusion power for 100 trillionths of a second,” LLNL reported on Aug. 18. It achieved a yield of more than 1.3 megajoules (MJ)—exceeding the 1-MJ threshold that researchers suggest is required for the onset of nuclear fusion ignition.
“The yield was significantly greater than the energy deposited in the hot spot by the implosion,” said Ed Moses, a former principal associate director for NIF and Photon Science. “This represents an important advance in establishing a self-sustaining burning target, the next critical step on the path to fusion ignition on NIF.”
Initial analysis suggests the 1.3 MJ output is an eightfold improvement over experiments conducted in spring 2021, and an increase of 25 times over NIF’s 2018 record yield. According to experts from the Imperial College of London, the results suggest the experiment produced more energy than any previous inertial confinement fusion experiment—and it proves ignition is possible.
Why Ignition Is Such an Important Step
Fusion happens when the nuclei of light atoms (like hydrogen) overcome the electrical resistance that keeps them apart, allowing them to get close enough to activate the strong nuclear force that “fuses” them together to form heavier elements (such as helium). To enable this “fusion,” fuel is heated to very high temperatures, forming a plasma—a cloud of charged ions—in which fusion reactions take place. During fusion reactions, several particles— including “alpha” particles—are released, and these interact with the surrounding plasma and heat it up further. The heated plasma then releases more and more alpha particles in a self-sustaining reaction—a process referred to as “ignition.”
Essentially, fusion “ignition” refers to the moment when the energy from a controlled fusion reaction outstrips the rate at which x-ray radiation losses and electron conduction cool the implosion. It must achieve “as much or more energy ‘out’ than ‘in,’ ” explains LLNL.
While the latest experiment still required more energy input than it put out, the effort is the first suspected to have reached that crucial, long-sought stage of “ignition,” which allowed considerably more energy to be produced than ever before. As crucially, it paves the way for “break-even,” where the energy in is matched by the energy out.
“Achieving ignition would be an unprecedented, game-changing breakthrough for science and could lead to a new source of boundless clean energy for the world,” LLNL said.
“Demonstration of ignition has been a major scientific grand challenge since the idea was first published almost 50 years ago. It was the principal reason for the construction of NIF and has been its primary objective for over a decade,” said Professor Jeremy Chittenden, co-director of Imperial’s Centre for Inertial Fusion Studies. “After 10 years of steady progress towards demonstrating ignition, the results of experiments over the last year have been more spectacular, as small improvements in the fusion energy output are strongly amplified by the ignition process,” he said.
“The pace of improvement in energy output has been rapid, suggesting we may soon reach more energy milestones, such as exceeding the energy input from the lasers used to kick-start the process.”
LLNL researchers and their colleagues have worked for the last six decades to refine their efforts to demonstrate fusion ignition. At NIF, the March 2009-completed facility that houses one of the world’s largest and most energetic lasers, fusion ignition is a primary objective. Experiments have focused on an “indirect drive” inertial confinement fusion approach, in which 192 laser beams at NIF 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,” LLNL said.
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,” it said. “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).”
The breakthrough results on Aug. 8 built on several advances gained from insights developed over the last several years on new diagnostics; target fabrication improvements in the hohlraum, capsule shell, and fill tube; improved laser precision; and design changes to increase the energy coupled to the implosion and the compression of the implosion, LLNL said.
Now, the team—which includes “collaborators” at Los Alamos National Laboratory and Sandia National Laboratories, the University of Rochester’s Laboratory for Laser Energetics, and General Atomics—will await a full scientific interpretation of their results through the peer-reviewed journal/conference process.
DOE Says This Is a Big Deal for National Security—but Academia, Industry Say It Has Clean Energy Implications
For LLNL and the U.S. Department of Energy (DOE), the achievement could unlock a significant new direction for nuclear weapons under the National Nuclear Security Administration’s (NNSA’s) “Path Forward” strategy. According to that strategy, which is outlined in a 2012 report to Congress, NIF’s pursuit of ignition and high fusion yields in the laboratory will illuminate understanding of high energy density (HED) science issues related to the nation’s nuclear weapons stockpile.
“These extraordinary results from NIF advance the science that NNSA depends on to modernize our nuclear weapons and production as well as open new avenues of research,” Jill Hruby, DOE undersecretary for Nuclear Security and NNSA administrator, said on Wednesday.
“This result is a historic step forward for inertial confinement fusion research, opening a fundamentally new regime for exploration and the advancement of our critical national security missions,” said LLNL Director Kim Budil.
Elsewhere around the world, however, the feat was celebrated as a potential breakthrough for clean energy. It brings demonstrating the feasibility of fusion energy—an energy resource that essentially replicates the process which powers the sun—a small step closer to fruition, suggested several experts. The achievement is another milestone that is fueling optimism for the long-sought but long-elusive energy source. The scientific community has suggested fusion energy is closer than many people realize.
Physicists at Imperial College London, which are helping to analyze the data from participating academic institutions, have already suggested the experiment was a success.
“While the NIF is primarily a physics experiment, and does not have the main goal of creating fusion energy, this incredible result means that this dream is closer to being a reality,” said Chittenden. “We have now proven it is possible to reach ignition, giving inspiration to other laboratories and start-ups around the world working on fusion energy production to try to realize the same conditions using a simpler, more robust, and above all cheaper method.”
Dr. Arthur Turrell, from the Department of Physics at Imperial put it another way: “The team at the National Ignition Facility, and their partners around the world, deserve every plaudit for overcoming some of the most fearsome scientific and engineering challenges that humanity has ever taken on. The extraordinary energy release achieved will embolden nuclear fusion efforts the world over, lending momentum to a trend that was already well underway.”
Dr. Aidan Crilly, research associate in the Centre for Inertial Fusion Studies at Imperial, added: “Reproducing the conditions at the center of the Sun will allow us to study states of matter we’ve never been able to create in the lab before, including those found in stars and supernovae,” he said. “We could also gain insights into quantum states of matter and even conditions closer and closer to the beginning of the Big Bang—the hotter we get, the closer we get to the very first state of the Universe.”
Industry Perspective: Energy Gain by Fusion ‘Imminent’
Offering an industry perspective, Dr. Georg Korn, co-founder and chief technology officer at Marvel Fusion—a firm that is making notable headway on commercial fusion energy through its work with highly concentrating ultra-short high-peak power lasers—also notably hailed the milestone as indicative “that energy gain by fusion is imminent.”
Marvel Fusion is looking to demonstrate proof of a net energy gain from fusion within the next two to four years and is targeting commercial use beginning in 2030. Korn told POWER the NIF achievement “is a massive milestone for the entire fusion community and the current success makes me even more optimistic for fusion than ever.” Lasers are becoming more and more powerful and are finally closing in on the necessary parameters for initiating fusion processes, he explained.
“These high-intensity lasers can be used to concentrate energy in a plasma and create conditions in which fusion reactions occur amply. While in the latest NIF experiments, the total energy released through fusion reactions is still less than the energy in the laser pulse (about 70%), the results illustrate the rapid pace of innovation in today’s fusion landscape. We are closer to our collective goals than ever before,” he said.
Korn suggested technology advancements will only open more opportunities. “Moving forward, the next generation of lasers, diode-pumped high repetition rate, will assist us in the urgent process of developing a clean, dense, and efficient technology, which, in turn, help solve the world’s energy crisis through large-scale decarbonized energy production. For physicists, like myself, the rapid advancement of lasers to that end is nothing short of revolutionary with much more to come,” he said.
—Sonal Patel is a POWER senior associate editor (@sonalcpatel, @POWERmagazine).