For six decades, scientists have been working towards realizing the concept of inertial confinement fusion, in which a fusion ignition releases more energy than it takes to put in. In December 2022, the National Ignition Facility at Lawrence Livermore National Laboratory achieved a historic breakthrough in science by facilitating a successful fusion ignition — a game changer for the future of nuclear defense and clean energy. 

The experiment required 192 laser beams, each longer than a football field, to hit a target of deuterium and tritium, heavier and radioactive isotopes of hydrogen, respectively. This small volume of hydrogen fuel was heated and compressed by the lasers, resulting in the fusion of atoms. UC Santa Barbara alum Sarah Nelson, acting office director of the Office of Experimental Sciences at the National Nuclear Security Administration (NNSA), helped oversee and manage the research and development program that achieved this. 

Fusing those atoms together is not something mother nature wants to do naturally, requiring extreme temperatures and pressures to overcome the repulsion between the nuclei,” explained Nelson. “Fusion is the power source of the Sun and other stars, where hydrogen nuclei such as deuterium (D) and tritium (T) are fused into helium. Researchers focus on DT reactions both because they produce large amounts of energy and they occur at lower temperatures than other elements.”

The experiment was successfully replicated by the Lawrence Livermore National Laboratory (LLNL) in August 2023, producing an even higher energy yield than that of the initial shot. The reproducibility of the experiment points toward a future of many other discoveries at the forefront of science that have capabilities to benefit society. 

One such benefit is maintaining the safety and security of the nuclear stockpile without resorting to nuclear testing. In addition, the breakthrough opens the possibility for a future of clean energy. According to Nelson, the two shots that have already been accomplished would need to happen 10 times a second to support something like a power plant. Although the research is far from being able to put energy on the grid, this experiment has shown that it is possible. 

Nelson, along with NNSA physical scientist Samantha Calkins, was recently named a Service to America Medals finalist for energy innovation. In light of this recognition, Nelson paid tribute to those who came before her. 

I am just the latest person, along with Samantha Calkins, to be filling these roles, and a number of people in the past have advocated for this program over the years,” Nelson said. “I feel so lucky and this is such an honor to be able to be doing this work right now.” 

Reflecting upon her career path, Nelson recalls her experience as a UCSB undergraduate student working in professor Steven Buratto’s lab in the Department of Chemistry and Biochemistry. Here she found a community of support, encouragement and freedom to explore the field of science. As an undergraduate student she enrolled in an internship program at the LLNL, the very place where the ignition breakthrough occurred. When Nelson received news of the experiment’s success, she recognized how far both she and the science had come.

“I thought back to the time when I was taking a tour of the National Ignition Facility in Livermore, California as an undergraduate before its construction had even finished,” Nelson recalled. “What a fantastic experience to witness when this machine was being constructed in 2002 [and then] to [be] the one who happens to be in the chair running this program in 2022.”

As a woman in S.T.E.M., Nelson encourages women to continue to pursue science and technology despite what others may say.

“The tide is changing,” Nelson said. “Do not let the opinions of others turn into your own voice. Women in science are just as valuable and should feel confident in their contributions.”

Nelson and the National Ignition Facility continue to conduct research to advance the progress of this recent achievement as well as improve the results of the ignition experiments and their potential applications.