Nuclear fusion is the ephemeral holy grail of climate technology. It would provide nearly limitless amounts of clean energy without the byproduct of long-lasting radioactive waste to be managed.

It’s also the biggest bet Silicon Valley luminary Sam Altman has ever made.

“This is the biggest investment I’ve ever made,” Altman told CNBC of his $375 million investment in Helion Energy, announced Friday. It’s part of a larger $500 million round that the start-up will use to complete the construction of a fusion facility near its headquarters in Everett, Washington.

Altman was the president of the Silicon Valley start-up shop Y Combinator from 2014 through 2019 and is now the CEO of Open AI, an organization that researches artificial intelligence, which he co-founded with Elon Musk and others. (Musk has since stepped away, citing conflicts of interest with Tesla’s AI pursuits.) Altman has also been a big proponent of universal basic income, the idea that the government should give every citizen a basic living wage to compensate for technological disruptions that make some jobs irrelevant.

Years ago, Altman had made a list of the technologies he wanted to get involved in, and artificial intelligence and energy topped that list.

Altman visited four fusion companies, and made his first investment of $9.5 million into Helion 2015.

“I immediately upon meeting the Helion founders thought they were the best and their technical approach was the best by far,” he said.

Nuclear fusion is the opposite reaction of nuclear fission: Where fission splits a larger atom into two smaller atoms, releasing energy, fusion happens when two lighter nuclei slam together to form a heavier atom. It’s the way the sun makes energy, and the basis of hydrogen bombs. Helion is one of a handful of start-ups working to control and commercialize fusion as an energy source, including Commonwealth Fusion Systems and TAE Technologies.

Perhaps the best-known fusion project is Iter in Southern France, where about 35 nations are collaborating to build a donut-shaped fusion machine called a tokamak.

Helion does not use a tokamak, said David Kirtley, Helion’s co-founder and CEO. The fusion machine Helion is building is long and narrow.

Helion uses “pulsed magnetic fusion,” Kirtley explained. That means the company uses aluminum magnets to compress its fuel and then expand it to get electricity out directly.

Extremely high temperatures are needed to create the create and maintain the delicate state of matter called plasma, where electrons are separated from nuclei, and where fusion can occur.

In June, Helion announced it exceeded 100 million degrees Celsius in its 6th fusion generator prototype, Trenta.

Kirtley compares Helion’s fusion machine to a diesel engine, while older technologies are more like a campfire. With a campfire, you stoke the fire to generate heat. In a diesel engine, you inject the fuel into a container, then compress and heat the fuel until it begins to burn. “And then you use the expansion of it to directly do useful work,” said Kirtley.

“By taking this new fresh approach and some of the old physics, we can we can move forward and do it fast,” Kirtley said. “The systems end up being a lot smaller, a lot faster to iterate, and then that gets us to commercially useful electricity, which is solving the climate change problem, as soon as possible.”

Helion Energy is using aneutronic fusion, meaning “they don’t have a lot high energy neutrons present in their fusion reaction,” according to Brett Rampal, the Director of Nuclear Innovation at the non-profit Clean Air Task Force.

There are still unknowns with aneutronic fusion, Rampal said.

“An aneutronic approach, like Helion Energy is pursuing, could have potential benefits that other approaches do not, but could also have different downsides and challenges to achieving commercial fusion energy production,” Rampal said.

Overall, though, Rampal believes the wave of investment and innovation in fusion over the last two decades is good news for the industry.

“With so much left to be proven for true commercial fusion approaches, coming at the problem from multiple different angles and trying to determine where the best pros and cons lie with individual technologies is exactly where the fusion industry should be right now,” Rampal told CNBC.

For Altman, fusion is part of his overall vision of increasing abundance through technological innovation — a vision that stands apart from many investors and thinkers in the climate space.

“Number one, I think it is our best shot to get out of the climate crisis,” Altman said.

More generally, “decreasing the cost of energy is one of the best ways to improve people’s quality of lives,” Altman said. “The correlation there is just incredibly big.”

Altman’s utopian vision encompasses three parts.

Artificial intelligence, Altman said, will drive the cost of goods and services down with exponential increases in productivity. Universal basic income will be necessary to pay people’s cost of living in the transition period where many jobs are eliminated. And virtually limitless, low-cost, green energy is the third part of Altman’s vision for the world.

“So for the same reason I’m so interested in AI, I think that fusion, as a path to abundant energy, is sort of the other part of the equation to get to abundance,” Altman told CNBC.

“I think fundamentally today in the world, the two limiting commodities you see everywhere are intelligence, which we’re trying to work on with AI, and energy, which I think Helion has the most exciting thing in the entire world happening for right now.”

But Altman knows that fusion has been elusive for decades. “The joke in fusion is that it’s been 30 years away for 50 years,” he said.

Kirtley was similarly dismayed by the seemingly impossibly time frames to commercialize fusion. “I got into fusion, spent a couple of years learning everything I could about fusion and all the typical approaches, and actually pivoted away from fusion. I said that these timelines don’t help us,” Kirtley told CNBC.

He worked with NASA, the Air Force and the Defense Advanced Research Projects Agency (DARPA) working on space propulsion technology to help humans travel to Mars and beyond.

But the idea of using approaching fusion with new technologies drew Kirtley back.

Kirtley joined his co-founders John Slough, George Votroubek and Chris Pihl to launch Helion in 2013. “We were able to show that there are actually new approaches to fusion that take modern technology — electronics, and fiber optics and computers — that haven’t been applied to the fusion industry as a whole,” Kirtley said.

The money from the round announced on Friday will be used to complete the construction of Polaris, Helion’s 7th generation fusion facility, which it broke ground on in July and which it aims to use to demonstrate net electricity production in 2024.

Other investors in Helion include LinkedIn founder Reid Hoffman, and Dustin Moskovitz, a Facebook co-founder. Moskovitz also participated again in Friday’s funding round.

The mission is personal for Kirtley, as tackling climate change is for so many. He moved from Southern California to Washington in 2008.

“I watch now Washington summers where we have fires now, and we didn’t when I first moved here,” he said. The urgency is tangible as they are “watching the glaciers melt on Mount Rainier.”