Man-made stars producing clean, cheap, almost limitless electricity. Like Wakanda’s vibranium, it sounds too good to be true, but a growing number of scientists, government officials and businesses believe that’s what nuclear fusion could provide and that it could be just a decade or so away.

Sceptics will point out that scientists working on nuclear fusion have been claiming it’s a decade or so away for much longer than a decade. And we have already have technologies which can produce clean, cheap and limitless electricity from the sun, wind and waves.

But, while they don’t dispute the urgency of renewable investment and that there are still obstacles to overcome, nuclear fusion advocates can point to a scientific breakthrough and growing momentum to suggest star power could help the world get and stay off fossil fuels, particularly towards the middle and end of this century.

What is nuclear fusion?

When we talk about nuclear power plants and nuclear bombs, we’re talking about nuclear fission. That’s splitting one nucleus into two, producing a load of energy which you can either use to spin a turbine to produce electricity or let off in an explosion.

Nuclear fusion produces energy by smashing hydrogen nucleuses together to produce heat and to spin a turbine to make electricity. Minus the turbine, it’s how the sun and others stars produce the energy which powers life on earth. Massachusetts Institute of Technology (MIT) nuclear fusion professor Dennis Whyte says that pursuing nuclear fusion is just listening to “Mother Nature”.

“It’s very important to listen to her,” he said in a TED talk. “She’s already told us that fusion is the power source of the universe.”

Is it clean?

Kind of. Whereas burning fossil fuels produce greenhouse gases, nuclear fusion produces only helium. That doesn’t cause climate change and it’s safe to breathe in. Millions of parents let their children take it into their lungs in order to talk in a funny high-pitched voice.

Like nuclear fission, nuclear fusion produces radioactive material which has to be stored until the radioactivity wears off.

Nuclear fusion advocates say the waste is not “long-lived” but how long is long?

International nuclear fusion project Iter say it can be recycled or reused within 100 years and the Max Planck Institute says that after 100-500 years, the radioactivity drops to a similar level to coal ash.

That’s similar to claims made by the nuclear fission industry – that, while their waste is “weakly radioactive for a few hundred thousand years, the radioactivity from the main component of the waste which could cause health problems will have decayed to safe levels within a few hundred years”.

Is it safe?

Yes. University of Oklahama research has shown that Americans associate “nuclear energy” with words like “dangerous”, “radiation” and “explosion”.

They’re thinking here of nuclear fission, which was responsible for mass destruction when Hiroshima and Nagasaki were bombed and when Chernobyl nuclear power plant exploded.

But, leaving aside debates about fission’s safety, fusion advocates say it is intrinsically much safer than nuclear fusion.

Nuclear fission reactors have to be kept cool. The Chernobyl, Fukushima and Three Mile Island nuclear fission plant failures were all because  cooling measures failed. Similarly, the current fear for Ukraine’s Zaporizhzhia power plant is that cooling systems will be disabled.

On the other hand, nuclear fusion reactors have to be kept very hot, around 100 million degrees C. If the outside world intrudes at all on a reactor, Whyte said, it won’t blow up. The reaction will fizzle out instantly.

Is it cheap to build?

Not yet. 30,000 construction workers are working 24/7 for Iter to build a fusion reactor in the south of France. It’s estimated to cost €20bn ($20bn) and was supposed to open in 2016.

Whyte’s students at MIT have made a breakthrough that he says will make reactors dramatically smaller, cheaper and faster to build.

To get a powerful reactor, you have to keep the stuff inside it (plasma) stable. The sun does that with its own magnetic field created by its sheer size.

To do that on earth, fusion reactors use very powerful donut-shaped magnets. The more powerful the magnets, the more powerful the reactor.

But the power of the magnets is limited because they run on electricity which is transported through copper wires. If the magnets are turned on for more than a few seconds, the electricity will burn the copper up.

Whyte presented his MIT students with this problem and they came up with the solution of replacing the copper with materials which don’t heat up known as superconductors.

Using these superconductors, an MIT spin-off called Commonwealth Fusion Systems hopes to build more powerful magnets to harness the plasma.

As they’re more powerful, the magnets can be smaller than Iter’s 17 m tall ones and the reactors also smaller, cheaper and quicker to build.

Is it cheap to run?

Not yet. As its not been produced commercially yet, it’s difficult to predict how much nuclear fusion could eventually cost.

Its advocates say, one the technology is sorted out, it will be cheap because its fuel is abundant.

When they say that, they are talking about deuterium. It’s found in any water source and costs just $13 a gram.

Whyte says the top inch of Boston harbour would provide all the deuterium necessary to power Boston with nuclear fusion for 100 years.

To make nuclear fusion energy, you smash deuterium into another type of hydrogen called tritium.

That’s much harder to get. Very little of it is present in nature and, while it can be made artificially, it currently costs about $30,000 a gram. An 800 MW nuclear fusion reactor would need around 300 grams a day. That would cost over $3bn a year to power just 130,000 homes.

Whyte told Climate Home that tritium is “not the fuel” and is “much more like a catalyst”.

In other words, you don’t need to keep feeding tritium into the reactor, you just need a little bit at the start and then the fusion reaction itself will produce more.

There’s about 30kg of tritium around now, mostly in Canada. “That’s sufficient to basically start the fusion economy going,” he said.

That’s in theory though. In practice, he said the technology “has not been demonstrated at scale yet”, although there are experiments at MIT and in the UK currently working on this problem.

Lithium is also needed. It lines the walls of a nuclear fusion reactor and scientists hope it will interact with the hydrogen to keep that tritium going around.

Compared to tritium, lithium is relatively abundant and is produced for electric vehicle batteries.

When will it be up and running?

The nuclear fusion developers timelines vary but all are uncertain.

Commonwealth Fusion Systems, who Whyte works with, hope to have a demonstration plan up and running in 2025 and electricity created and sold to the grid by the early 2030s.

The US government is working with private companies a plan to get pilot plants by around 2030 despite the government’s official scientific advisors recommending a 2035-2040 target.

China has a fusion programme too, whose timeline is unclear, while the mainly EU-funded Iter plans to generate “industrial-scale” fusion energy by 2050.

The UK’s new post-Brexit Advanced Research and Invention Agency (ARIA) want to beat that by getting fusion power on the grid by 2040.

Is it popular?

It’s too early to tell, as no public opinion surveys have been done.

But Kuhika Gupta, who researches public views of nuclear fission at Oklahoma University told Climate Home that “most people would be open to the idea of fusion”.

She suspected that support would be similar to levels for so-called “advanced fission” reactors, which are more popular than existing nuclear fission reactors.

“A lot of these initial views would be based on technological optimism and the positive idea of innovation,” she said, “but as the technology develops and advocacy coalitions supporting and opposing fusion take shape, we could expect those initial views to shift”.

Some nuclear fusion supporters want to brand it as “fusion technology” to avoid the negative connotations the word “nuclear” has.

Who will get rich off it?

Rich people. Nuclear fusion is being backed financially by governments and big corporations and billionaires from the wealthy world. They include fossil fuel companies like Chevron and Eni, US technology giant  Google and Japanese conglomerate Sumitomo.

Silicon Valley venture capitalists have bet on it too, like tech investor Sam Altman, Amazon boss Jeff Bezos and Donald Trump-supporting billionaire Peter Thiel.

Because of its size and complexity, fusion plants aren’t likely to be owned by local communities or regular individuals like solar and wind farms can be.