Energy from fusion: What is the promise? What hurdles remain?

The Explainer

It’s a question that has been tantalizing scientists for almost a century: Can humans tap the same force that powers the stars? On Dec. 5, an experiment by scientists in California signaled yes. Researchers at the Lawrence Livermore National Laboratory (LLNL) in California produced a brief nuclear fusion reaction resulting in a net energy gain, or more energy created than was used to start the reaction. 

It took years of effort, but collaboration and innovation turned hope into reality. 

At least for a fraction of a second. More advances are needed to bring nuclear fusion into practical use. And the work comes with controversy, since the research has military as well as civilian applications. But the potential benefit – a future with abundant and relatively clean energy – gives hope to many scientists and environmentalists alike. 

What is nuclear fusion?

Nuclear fusion is the energy that powers the sun and other stars – a process first theorized by British physicist Arthur Eddington in 1920. It occurs when two atoms combine, or fuse together, to make a heavier one. Fusion releases energy because the mass of the new singular nucleus is less than the mass of the two before, and the leftover mass becomes energy. 

When applied to energy production on Earth, fusion will be very different from the fission reactions used in nuclear power plants today. Fission involves splitting a nucleus into two smaller nuclei. Less energy is produced with nuclear fission, and the resulting waste is much more radioactive. Where fusion involves light gases (types of hydrogen), fission generally uses heavy elements like uranium.

Why was this experiment so important?

For one thing, it’s a sign that persistence and collaboration can pay off after decades of effort dating back as far as the 1950s. 

“There were a lot of times where people, even leadership, were like, ‘It’s not going to work. This is not going to do it,’” says Ryan McBride, a nuclear engineering professor at the University of Michigan. “And finally, they stuck with it and figured out how to get it working, which is really impressive.” 

The breakthrough came down to lasers focused on a small capsule of fuel.

Around 1 a.m. on Dec. 5, data from the experiment at the LLNL’s National Ignition Facility began to pour in. The team realized it had reached “ignition,” or the creation of more energy than what was used to start the reaction. One researcher said it brought her to tears. 

The facility’s 192 lasers – the world’s largest laser system, in a building the size of a sports stadium – were aimed at a
diamond-coated capsule the size of a peppercorn. That creates the immense pressure and temperature required (several times hotter than the sun’s core). The landmark test delivered 2.05 megajoules of energy to the target and resulted in 3.15 MJ of fusion energy output. But the tiniest differences in the capsule can create a different result each time.

There were two design changes that helped create the desired result. The capsule that held the fusion fuel was made thicker, and the power of the lasers was turned up by 8% while their symmetry was adjusted, says Arthur Pak, the team lead of stagnation science in the lab’s fusion work. 

The success was hailed as a win for military as well as civilian science. (The experiment was funded by the Department of Energy’s National Nuclear Security Administration, which focuses on nuclear warfare.) It signals fusion’s potential to replace underground tests for nuclear weapons. 

“That gives credibility to certifying our nuclear weapons stockpile and making sure that they can be as safe and secure and reliable as possible, especially in the era of not testing them,” says Dr. McBride. 

The experiment’s wider message for the world is simple, however: We finally know that ignition is possible. 

“I hope the public will ... realize that they shouldn’t be asking questions about how practical it is at the beginning, because first you have to know that it can be done,” says Paul Bellan, a plasma physicist at the California Institute of Technology. “Then you start making it practical.” 

What is the potential benefit? 

It’s nothing less than “clean, carbon free, abundance – reliable energy capable of meeting the world’s energy demands,” said Tammy Ma, the lead for LLNL’s institutional initiative, during a panel announcing the revolutionary achievement. 

Fusion’s radioactive waste has a relatively short half-life, posing little threat, scientists say. They add that there is no risk of meltdown, because fusion stops within seconds without ongoing inputs of energy to sustain it. 

Already, universities and the private sector are teaming up in efforts to make fusion practical, with ways to convert heat from plasma into electricity. Commonwealth Fusion Systems, for example, aims to build a fusion plant by the early 2030s by working with the Massachusetts Institute of Technology. Their focus: magnetic fusion. 

It’s a different approach to fusion than lasers, or inertial fusion. In magnetic fusion, magnets are used to contain the fuel that becomes energy-producing plasma (heated by electric current). 

“We set up this collaboration agreement with MIT that effectively allowed us to be born in scale,” says Brandon Sorbom, co-founder and chief scientist at Commonwealth Fusion Systems, based in Cambridge, Massachusetts. “We started with a fully functioning lab with 50 years of history and experts in their respective field that have been working on fusion for decades in some cases. And that really was able to sort of catapult us into getting results faster.”

What hurdles remain? 

There are both scientific and technical challenges, says Mr. Pak at LLNL. The biggest: increasing the efficiency of the process. The 3 MJ of fusion energy created on Dec. 5 was greater than the 2 MJ of laser energy fired at the capsule, but 300 MJ of power was used to make those laser bursts. 

Beyond that, the process needs to be sustained over time and at scale. The fuel capsule in the experiment would power about 10 teakettles. To run a power plant, much more fuel would be needed, and lasers would need to shoot about every 10 seconds – something the National Ignition Facility can’t currently do.

Resources are another issue. Although deuterium is plentiful, there is the possibility that tritium, the other gas needed in the capsule, could run out. There are trace amounts in the atmosphere, but scientists say that tritium can be produced, or that eventually fusion will only need deuterium. 

For all the challenges, nations from Europe to China are chasing the fusion dream. 

“The pursuit of fusion ignition in the laboratory is one of the most significant scientific challenges ever tackled by humanity,” LLNL Director Kim Budil said at a press briefing last month. “Achieving it is a triumph of science, engineering, and most of all, people.”