NIF Laser Systems Chief Engineer to Discuss Historic Fusion Ignition Achievement at Photonics West 2023

Photonics & Imaging Technology INSIDER

On Dec. 5, 2022, Lawrence Livermore National Laboratory's (LLNL) Nuclear Ignition Facility (NIF) made history, demonstrating fusion ignition for the first time in a laboratory setting.

LLNL officials and scientists confirmed that, for a fraction of a second, LLNL researchers produced 3.15 megajoules (MJ) of fusion energy output using 2.05 MJ of laser energy delivered to the target, demonstrating the fundamental science basis for inertial fusion energy. The results were peer-reviewed and verified by outside parties, scientists said.

Hailed by government officials as a watershed moment for fusion energy, the results are a “proof of concept” that a thermonuclear fusion reaction — the same reaction that powers the sun and stars — can be reproduced in the laboratory and result in a net energy gain, opening doors to a new scientific understanding of fusion and technological advancements in national defense and energy production.

During a live-streamed technical panel held after the achievement, experts from NIF further discussed the broader implications of this historic breakthrough. NIF’s Program Director for Weapon Physics and Design Mark Herrmann moderated the panel, providing an overview of NIF and a play-by-play of the historic shot.

Herrmann said on Dec. 5, NIF scientists performed a NIF shot as they always do — firing the facility’s 192 powerful lasers onto a BB-sized target of deuterium and tritium (DT), heavier isotopes of hydrogen. However, in this experiment, the laser energy was upped to 2.05 MJ, and conditions of implosion symmetry, heat and compression were just right, generating the record-breaking energy output of 3.15 MJ.

“There's a race between heating and cooling and if that plasma gets a little bit hotter, the fusion reaction rate goes up, creating even more fusions, which gets even more hot — so the question is, can we win the race?” Hermann said. “For many decades, we lost the race, and we got more cooling out than we got the heating up, so we didn't get to this ignition event. But last Monday, that all changed, and we able were able to win the race and get very significant heating of the fusion plasma up to very high temperatures.”

Considered the “holy grail” of fusion energy research, ignition comes just over a year after NIF reached a then-record-setting 1.3 megajoule shot, which produced about 70 percent of the energy put into the experiment via fusion reaction, planting NIF firmly on the doorstep of the milestone.

Researchers attributed the success after previous near misses to a combination of improvements in target design, better predictive modeling backed by machine learning and “cognitive simulation,” advances in laser capabilities and other adjustments.

Annie Kritcher, team lead for Integrated Modeling and the principal designer for the experiment, said the shot was part of a new NIF campaign that began in September, where the team introduced a new laser capability and a thicker capsule for the fusion fuel, providing more margin for achieving ignition. The team also made changes to improve implosion symmetry, which were fed to a cognitive simulation design team that determined there was high probability of a “yield gain of at least one,” Kritcher said.

Given the recent advancements and promising models, team members said they had “high hopes” and “good reasons to be optimistic” that the Dec. 5 shot would be extraordinary.

Arthur Pak, team lead for Stagnation Science, said that the team confirmed the net energy yield using multiple independent diagnostics to measure the number of neutrons that escaped the reaction, including radioactive decay and a magnetic spectrometer, giving them “high confidence” in the results.

Pak credited the breakthrough to the “tireless work of technicians and operators” that make observations of fusion plasma with improved diagnostics. Chief Engineer for the NIF Laser System Jean-Michel Di Nicola said the team stood “on the shoulders of multiple generations of optical, material and laser physicists who have designed and optimized ever-increasing performance in terms of laser delivery.” Principal Experimentalist Alex Zylstra, representing the experimental team, said the effort built on knowledge gained from a long history of previous experiments with specialized configurations and new diagnostics.

“All that work led up to a moment just after 1 a.m. last Monday when we took a shot and as the data started to come in, we saw the first indications that we'd produced more fusion energy from the laser inputs,” Zylstra said.

In addition to describing the behind-the-scenes work of the history-making shot to attendees and media, team members shared personal stories of hearing of the news of ignition later that morning.

Kritcher said she’d had “vivid dreams of possible outcomes” prior to the event and awoke to excited texts from Zylstra, informing her of ignition.

“You start looking and you see one diagnostic and you think, ‘well, maybe that's not real.’ And then you start to see more and more diagnostics, rolling and pointing to the same thing,” Kritcher said. “It was just a great feeling.”

Tammy Ma, who leads the Laboratory’s Inertial Fusion Energy (IFE) Institutional Initiative, said she was at the San Francisco International Airport waiting to board a plane for Washington when her phone rang.

“I got a call from my boss saying, ‘I think we got ignition,’ and I burst into tears,” Ma recalled. “I was jumping up and down in the waiting area — the crazy person. And yeah, the tears were streaming down my face.”

Looking to the future, Ma said ignition “lays the groundwork” for the feasibility of inertial fusion energy and creates a roadmap for reaching even higher energy gains and, potentially, a pathway to pilot commercial fusion plants in the coming decades.

“Developing an economically attractive approach to fusion energy is a grand scientific and engineering challenge — without a doubt, it will be a monumental undertaking,” Ma said. “However, the potential benefits are enormous; clean, carbon-free, abundant reliable energy capable of meeting the world's energy demands, and furthermore, providing for the energy sovereignty and energy security of the U.S.”

Ma said that an upcoming DOE Office of Fusion Energy report will set the framework for a new IFE program in the U.S., which is currently at a “divergent point” where more investments are needed to make the technology simpler and more efficient, and to determine the best design for fusion energy.

“Such a program will inevitably require participation from across the community, both the public sector but the private sector as well,” Ma said. “We look forward to working with the Department of Energy to leverage and capitalize on these great results for a fusion energy future. The time is now.”

As impressive as the ignition accomplishment is, researchers said they already have their sights set on future improvements for fusion experiments at NIF. Next summer, Di Nicola said, the team will design experiments and field shots with additional laser energy, providing them with more margins for ignition, and, with more investments, could produce even larger target gains. Target Fabrication Program Manager Michael Stadermann added that the target capsule used in the ignition shot had flaws, which was “very encouraging” for the team.

“This gives us confidence that we can make shells of equal quality and better quality in the future, and that we'll be able to reproduce this experiment or even improve on it,” Stadermann said.

Di Nicola will discuss the next steps for NIF and an outlook to future high yield applications and the pursuit of Inertial Fusion Energy during his presentation on the first day of Photonics West LASE.

Source¹ 

Source² 

---