Rerun: The Clean Energy Potential of Nuclear Fusion, with Annie Kritcher

Rectangular blue tiles are aligned, overlapping, in a circular pattern around a central focal point.

Image: The target chamber of the National Ignition Facility (NIF), at the Lawrence Livermore National Laboratory in northern California, is the destination for pulses shot from high-powered lasers. The NIF’s precise engineering assures the accuracy of the laser beam, down to the equivalent of the diameter of a human hair. Image by: Lawrence Livermore National Security.

Script by: Marie Hogan Blurb by: Elizabeth Sherstinsky Audio editing by: Xu Wangyuxan

What is nuclear fusion?

Nuclear fusion produces energy by fusing atoms together. Atomic cores (nuclei) merge together to form a heavier—though unstable—nucleus, releasing mass to regain stability. This mass release corresponds to an energy release, given Einstein’s equation E=mc2, which says in part that mass and energy can be converted into each other. The sun, along with all other stars, uses nuclear fusion to generate energy, which is released as heat and light. 

The 2022 Fusion Breakthrough 

In late 2022, scientists led by Dr. Annie Kritcher at the Lawrence Livermore National Laboratory (LLNL) briefly replicated the power of the sun. Replicating the sun’s power requires replicating the extreme heat and density conditions within the sun’s core. Atomic cores are positively charged, meaning they repel each other. To overcome this barrier, scientists need to apply massive amounts of heat and keep atomic cores extremely close together. For the first time, scientists produced more energy from fusion than the amount of energy it took to maintain these conditions. 

Fusion is a greenhouse-gas-free source of potentially unlimited electricity, powered by hydrogen we can take from water, and creating no long-lived radioactive waste. According to the International Atomic Energy Agency, fusion generates four times more energy per kilogram than the fission used for powering nuclear plants, and nearly 4 million times more energy than burning fossil fuels for energy. 

What’s Next?

Commercial nuclear fusion is still a long way off. While the physics aspect of fusion is “solved,” fusion remains a complicated engineering problem. The National Ignition Facility (NIF) at Lawrence Livermore National Laboratory has the most powerful laser in the world to blast heat at atoms, but it is the size of three football stadiums, very old, slow, inefficient, and clunky. There are still unanswered questions, such as how to affordably capture fusion energy, and how to keep a fusion reaction going for a long period of time. And although the laser shots at the NIF were weaker than its fusion output, the amount of energy drawn from the grid to create those lasers is 120 times more than the fusion output generated at LLNL. 

About Dr. Annie Kritcher

Dr. Annie Kritcher is a nuclear engineer and physicist at the National Ignition Facility at Lawrence Livermore National Laboratory Weapons and Complex Integration’s Design Physics Division. She led the recent nuclear fusion breakthrough at LLNL. In 2022, Kritcher was elected fellow of the American Physical Society. She earned her PhD at UC Berkeley. 

Further reading

A shot for the ages: Fusion ignition breakthrough hailed as ‘one of the most impressive scientific feats of the 21st century’ | Lawrence Livermore National Laboratory 

UK Power Grid Could Have First Commercial Fusion Reactor By 2030s

World’s largest nuclear fusion reactor promises clean energy, but the challenges are huge – ABC News

Annie Kritcher leads revolutionary nuclear fusion experiment 

IAEA, What is nuclear fusion?

NOVA Now, Universe Revealed Podcast, Can we Recreate the Power of Stars Down on Earth? (YouTube or NOVA Podcast website)


Ethan: I’m Ethan Elkind, and you’re listening to Climate Break—climate solutions in a hurry. Today’s proposal? Using nuclear fusion to generate carbon-free electricity. Unlike nuclear fission made famous by the atomic bomb, nuclear fusion produces energy by fusing together hydrogen isotopes. It’s been an elusive but ultimately unattainable goal. That is until a recent breakthrough at Lawrence Livermore National Laboratory in California. Physicist Annie Kritcher led the team that made this advance. She explains fusion’s promise.

Dr. Kritcher: Fusion is nice because it offers clean, unlimited energy, powered by isotopes of hydrogen which occur in water and do not create any long-lived radioactive waste.

Ethan: But fusion requires energy-intensive conditions: heat and pressure even more extreme than the center of the sun. In the past, that’s meant the process required more energy input than it actually produced. But Kritcher’s team broke this barrier. 

Dr. Kritcher: For the first time we got more fusion energy out than the amount of energy that was required to drive the system. 

Ethan: She credits the breakthrough to a more energy-efficient design. But she says we’re still years away from scaling up to full-scale nuclear fusion power plants operating outside of the laboratory setting.

Dr. Kritcher: Achieving ignition and fusion gain greater than one proves there’s nothing fundamentally limiting us from using fusion as a controlled energy source. So we’ve basically answered  the really hard physics questions and now it’s just getting the engineering to catch up.

Ethan: Learn more about Kritcher’s lab and the energy possibilities of nuclear fusion at

Rerun: The Clean Energy Potential of Nuclear Fusion, with Annie Kritcher