It was touted as a “major scientific breakthrough” and, it seems, the rumors were true: On Tuesday, scientists at Lawrence Livermore National Laboratory announced that they have, for the first time, achieved net energy gain in a controlled fusion experiment.

“We have taken the first tentative steps toward a clean energy source that could revolutionize the world,” Jill Hruby, administrator of the National Nuclear Security Administration, said in a press conference Tuesday.

The triumph comes courtesy of the National Ignition Facility at LLNL in San Francisco. This facility has long tried to master nuclear fusion — a process that powers the sun and other stars — in an effort to harness the massive amounts of energy released during the reaction because, as Hruby points out, all that energy is “clean” energy.

Despite decades of effort, however, there had been a major kink in these fusion experiments: the amount of energy used to achieve fusion has far outweighed the energy coming out. As part of the NIF mission, scientists had long hoped to achieve “ignition,” where the energy output is “greater than or equal to laser drive energy.”

Some experts have remained skeptical that such a feat was even possible with fusion reactors currently in operation. But slowly, NIF pushed forward. In August last year, LLNL revealed it had come close to this threshold by generating around 1.3 megajoules (a measure of energy) against a laser drive using 1.9 megajoules.

But on Dec. 5, LLNL’s scientists say, they managed to cross the threshold.

They achieved ignition.

All in all, this achievement is cause for celebration. It’s the culmination of decades of scientific research and incremental progress. It’s a critical, albeit small, step forward, to demonstrate that this type of reactor can, in fact, generate energy.

“Reaching ignition in a controlled fusion experiment is an achievement that has come after more than 60 years of global research, development, engineering and experimentation,” Hruby said.

“It’s a scientific milestone,” Arati Prabhakar, policy director for the White House Office of Science and Technology, said during the conference, “but it’s also an engineering marvel.”

Still, a fully operational platform, connected to the grid and used to power homes and businesses, likely remains a few decades away.

“This is one igniting capsule at one time,” Kim Budil, director of LLNL, said. “To realize commercial fusion energy you have to do many things. You have to be able to produce many, many fusion ignition events per minute, and you have to have a robust system of drivers to enable that.”

So how did we get here? And what does the future hold for fusion energy?

Simulating stars

The underlying physics of nuclear fusion has been well understood for almost a century.

Fusion is a reaction between the nuclei of atoms that occurs under extreme conditions, like those present in stars. The sun, for instance, is about 75% hydrogen and, because of the all-encompassing heat and pressure at its core, these hydrogen atoms are squeezed together, fusing to form helium atoms.

If atoms had feelings, it would be easy to say they don’t particularly like being squished together. It takes a lot of energy to do so. Stars are fusion powerhouses; their gravity creates the perfect conditions for a self-sustaining fusion reaction and they keep burning until all their fuel — those atoms — are used up.

This idea forms the basis of fusion reactors.

Building a unit that can artificially re-create the conditions within the sun would allow for an extremely green source of energy. Fusion doesn’t directly produce greenhouse gases, like carbon dioxide and methane, which contribute to global warming.

And critically, a fusion reactor also doesn’t have the downsides of nuclear fission, the splitting of atoms used in nuclear bombs and reactors today.

In other words, a fusion power plant wouldn’t produce the radioactive waste associated with nuclear fission.

The big fusion experiment

The NIF, which takes up the space of around three football fields at LLNL, is the most powerful “inertial confinement fusion” experiment in the world.

In the center of the chamber lies a target: a “hohlraum,” or cylinder-shaped device that houses a tiny capsule. The capsule, about as big as a peppercorn, is filled with isotopes of hydrogen, deuterium and tritium, or D-T fuel, for short. The NIF focuses all 192 lasers at the target, creating extreme heat that produces plasma and kicks off an implosion. As a result, the D-T fuel is subject to extreme temperatures and pressures, fusing the hydrogen isotopes into helium — and a consequence of the reaction is a ton of extra energy and the release of neutrons.

You can think of this experiment as briefly simulating the conditions of a star.

The complicated part, though, is that the reaction also requires a ton of energy to start. Powering the entire laser system used by the NIF requires more than 400 megajoules — but only a small percentage actually hits the hohlraum with each firing of the beams. Previously, the NIF had been able to pretty consistently hit the target with around 2 megajoules from its lasers.

But on Dec. 5, during one run, something changed.

“Last week, for the first time, they designed this experiment so that the fusion fuel stayed hot enough, dense enough and round enough for long enough that it ignited,” Marv Adams, deputy administrator at the NNSA, said during the conference. “And it produced more energy than the lasers had deposited.”

More specifically, scientists at NIF kickstarted a fusion reaction using about 2 megajoules of energy to power the lasers and were able to get about 3 megajoules out. Based on the definition of ignition used by NIF, the benchmark has been passed during this one short pulse.

You might also see that energy gain in a fusion reaction is denoted by a variable, Q.

Like ignition, the Q value can refer to different things for different experiments. But here, it’s referring to the energy input from the lasers versus the energy output from the capsule. If Q = 1, scientists say they have achieved “breakeven,” where energy in equals energy out.

The Q value for this run, for context, was around 1.5.

In the grand scheme of things, the energy created with this Q value is only about enough to boil water in a kettle.

“The calculation of energy gain only considers the energy that hit the target, and not the [very large] energy consumption that goes into supporting the infrastructure,” said Patrick Burr, a nuclear engineer at the University of New South Wales.

The NIF is not the only facility chasing fusion — and inertial confinement is not the only way to kickstart the process. “The more common approach is magnetically confined fusion,” said Richard Garrett, senior advisor on strategic projects at the Australian Nuclear Science and Technology Organization. These reactors use magnetic fields to control the fusion reaction in a gas, typically in a giant, hollow donut reactor known as a tokamak.

Those devices have a much lower density than NIF’s pellets, so temperatures need to be increased to well over 100 million degrees. Garrett said he does not expect the NIF result to accelerate tokamak fusion programs because, fundamentally, the two processes work quite differently.

However, significant progress is also being made with magnetically confined fusion. For instance, the ITER experiment, under construction in France, uses a tokamak and is expected to begin testing in the next decade. It has lofty goals, aiming to achieve a Q greater than 10 and to develop commercial fusion by 2050.

The future of fusion

The experiment at NIF might be transformative for research, but it won’t immediately translate to a fusion energy revolution. This isn’t a power-generating experiment. It’s a proof of concept.

This is a point worth paying attention to today, especially as fusion has often been touted as a way to combat the climate crisis and reduce reliance on fossil fuels or as a salve for the world’s energy problems. Construction and utilization of fusion energy to power homes and businesses is still a ways off — decades, conservatively — and inherently reliant on technological improvements and investment in alternative energy sources.

Generating around 2.5 megajoules of energy when the total input from the laser system is well above 400 megajoules is, of course, not efficient. And in the case of the NIF experiment, it was one short pulse.

Looking further ahead, constant, reliable, long pulses will be required if this is to become sustainable enough to power kettles, homes or entire cities.

“It’s unlikely that fusion power … will save us from climate change,” said Ken Baldwin, a physicist at the Australian National University. If we are to prevent the largest increases in global average temperature, fusion power is likely going to be a little too late.

Other investment is going to come from private companies, which are seeking to operate tokamak fusion reactors in the next few years. For instance, Tokamak Energy in the UK is building a spherical tokamak reactor and seeks to hit breakeven by the middle of this decade.

Then there’s Commonwealth Fusion Systems, spun out of MIT, which is hoping to generate around 400 megawatts of power, enough for tens of thousands of homes, by the 2030s. Modern nuclear power plants can produce almost three times as much.

And as CNET editor Stephen Shankland noted in a recent piece, fusion reactors will also need to compete against solar and wind power — so even with today’s revelatory findings, fusion energy remains entrenched in the experimental phase of its existence.

But we can now cast one eye toward the future.

It may not prevent the worst of climate change but, harnessed to its full potential, it could produce a near-limitless supply of energy for generations to come. It’s one thing to think about the future of energy on Earth and how it will be utilized, but our eyes may fall on horizons even further out — deep space travel could utilize fusion reactors that blast us well beyond the reaches of our sun’s gravity, the very thing that helped teach us about fusion reactions, and into interstellar space.

Perhaps then, we’d remember Dec. 5, 2022, as the first tiny step toward places we dared once only dream about.

Correction, 8:44 a.m. PT: This article initially misstated the amount of energy in the fusion reaction. NIF powered the lasers with about 2 megajoules and produced 3 megajoules as a result.