For decades, scientists have been predicting that, one day, the same process that powers the sun will give us virtually unlimited cheap, clean electricity. Are they wrong

A star is born. And, less than a second later, it dies. On a drab science park just outside the Oxfordshire village of Culham, some of the world's leading physicists stare at a monitor to review a video of their wondrous, yet fleeting, creation.

"Not too bad. That was quite a clean one," observes starmaker-in-chief Professor Steve Cowley. Just a few metres away from his control room, a "mini star" not much larger than a family car has just burned, momentarily bright, at temperatures approaching 23 million degrees centigrade inside a 70-tonne steel vessel.

Cowley sips his coffee. "OK, when do we go again?"

Last year, when asked to name the most pressing scientific challenge facing humanity, Professors Stephen Hawking and Brian Cox both gave the same answer: producing electricity from fusion energy. The prize, they said, is enormous: a near-limitless, pollution-free, cheap source of energy that would power human development for many centuries to come. Cox is so passionate about the urgent need for fusion power that he stated that it should be scientists such as Cowley who are revered in our culture – not footballers or pop stars – because they are "literally going to save the world". It is a "moral duty" to commercialise this technology as fast as possible, he said. Without it, our species will be in "very deep trouble indeed" by the end of this century.

If only it were that simple. Fusion energy – in essence, recreating and harnessing here on earth the process that powers the sun – has been the goal of physicists around the world for more than half a century. And yet it is perpetually described as "30 years away". No matter how much research is done and money is spent attempting to commercialise this "saviour" technology, it always appears to be stuck at least a generation away.

Cowley hears and feels these frustrations every day. As the director of the Culham Centre for Fusion Energy, he has spent his working life trying to shorten this exasperating delay. Fusion energy is already a scientific challenge arguably more arduous than any other we face, but recent events have only piled on further pressure: international climate-change negotiations have stalled; targets to ramp up renewable energy production seem hopelessly unrealistic; and the Fukushima disaster has cast a large shadow over the future of fusion's nuclear cousin, fission energy, with both Germany and Italy stating that, owing to safety concerns, they now intend to turn their back on a source of energy which has been providing electricity since the 1950s.

But today Cowley seems upbeat, chipper even. After an 18-month shutdown to retile the interior of the largest of the centre's two "tokamaks" – ring doughnut-shaped chambers where the fusion reaction takes place – he is bullish about the progress being made by the 1,000 scientists and engineers based at Culham.

"By 2014-15, we will be setting new records here. We hope to reach break-even point in five years. That will be a huge psychological moment."

Cowley is referring to the moment of parity when the amount of energy they extract from a tokamak equals the amount of energy they put into it. At present, the best-ever "shot" – as the scientists refer to each fusion reaction attempt – came in 1997 when, for just two seconds, the JET (Joint European Torus) tokamak at Culham achieved 16MW of fusion power from an input of 25MW. For fusion to be commercially viable, however, it will need to provide a near-constant tenfold power gain.

So, what are the barriers preventing this great leap forward?

"We could produce net electricity right now, but the costs would be huge," says Cowley. "The barrier is finding a material than can withstand the neutron bombardment inside the tokamak. We could also just say damn to the cost of the electricity required to demonstrate this. But we don't want to do something that cannot be shown to be commercially viable. What's the point?"

At the heart of a star, fusion occurs when hydrogen atoms fuse together under extreme heat and pressure to create a denser helium atom releasing, in the process, colossal amounts of energy. But on Earth, scientists have to try and replicate a star's intense gravitational pressure with an artificial magnetic field that requires huge amounts of electricity to create – so much that the National Grid must tell Culham when it is OK for them to run a shot. (Namely, not in the middle of Coronation Street or a big football match.)

The fusion reaction occurs when the fuel (two types, or isotopes, of hydrogen known as deuterium and tritium) combines to form a super-hot plasma which produces, alongside the helium, neutrons which have a huge amount of kinetic energy. The goal of plasma physicists such as Cowell is to harness the release of these neutrons and use their abundant energy to drive conventional turbines to generate electricity. The JET tokamak has been shut down for the past 18 months while the interior has been stripped of its 4,500 carbon tiles and replaced with new tiles made from beryllium and tungsten. The hope is that these new tiles will be far more "neutron resilient", allowing for shots to be conducted for longer periods and at much higher temperatures.

Over lunch at the staff canteen, Francesco Romanelli, the Italian director of the European Fusion Development Agreement, the European agency that funds JET, explains why the new tiles are so crucial: "We now understand how a plasma works. We have demonstrated with JET that we can contain the reactants; we reach temperatures 20 times hotter than the sun's core and we produce an intense magnetic field, 1,000 times that of Earth's normal magnetic field. But the main problem we face is plasma turbulence. To compensate for this loss, we have to add more heat and energy. So we are always looking for materials that can withstand these extraordinary conditions inside the tokamak."

Last year, bulldozers began clearing land 60km north-east of Marseille in southern France. By 2019, it is hoped that the world's largest and most advanced experimental tokamak will be switched on. The €15bn International Thermonuclear Experimental Reactor (ITER) is being funded by an unprecedented international coalition, including the EU, the US, China, India, South Korea and Russia. Everything learned at Culham will be fed into improving the design and performance of ITER which, it is hoped, will demonstrate the commercial viability of fusion by producing a tenfold power gain of 500MW during shots lasting up to an hour.

But ITER's projected costs are already rocketing, and politicians across Europe have expressed concern, demanding that budgets be capped. Fusion energy also has its environmental detractors. When the ITER project was announced in 2005, Greenpeace said it "deplored" the project, arguing that the money could be better spent building offshore wind turbines. "Advocates of fusion research predict that the first commercial fusion electricity might be delivered in 50-80 years from now," said Jan Vande Putte, Greenpeace International's nuclear campaigner. "But most likely, it will lead to a dead end, as the technical barriers to be overcome are enormous." Meanwhile, there is criticism from some plasma physicists that the design of ITER is wrong and alternative designs might produce better results for much less money.

Romanelli rejects this analysis. We simply must make this investment, he says: "The prize on offer is too tantalising to ignore. Fusion doesn't produce greenhouse gases, it is intrinsically safe and it leaves no burden on future generations. The primary reaction does not produce nuclear material, only helium. There's a limited problem in that you produce neutrons, but this only makes the reactor chamber itself radioactive. Within 100 years, you could recycle the chamber so there's no need for geological-timescale storage as there is with the waste from fission energy. And the fuel is virtually unlimited. All you need is lithium and hydrogen. Sea water alone could fuel current human consumption levels for 30 million years."

Another major positive promised by fusion, says Romanelli, is that reactors would be so safe that they could be located amid urban centres where the power is most needed. "A tsunami, earthquake or bomb could hit a fusion reactor and the problems caused would only ever be structural. With fission, you have to release the energy if there's a problem, whereas fusion shuts down instantly if disrupted."

If fusion offers such glorious bounty, it prompts the question – given, say, our concerns over climate change and the global political instability caused by the pursuit of oil – why the world isn't concentrating much harder on delivering it as fast as possible. Yes, €15bn is a lot of money to be spending building ITER. But, by comparison, the global cosmetics and perfume industry is worth some $170bn a year. And, in 2010, the US's military budget was $663bn. If the motivation was there, the global community could find the money to fund 10 rival fusion projects to fast-track the process of finding the optimum design. So, why haven't we seen a Manhattan Project-style push for fusion such as we did during the second world war when it was deemed by the allied forces that they must beat the Nazis in the race to build the first atomic bomb?

"People – and particularly politicians – still remember fission's early claims that it would produce electricity that was 'too cheap to meter'," says Cowley. For most people, fusion is the realm of science fiction and it is hard to convince them that it should be a strategic priority, he says. "We scientists have to be honest, too: we thought it would be easy to crack fusion. But there's no other comparable challenge. There is no model for this technology. The first flying devices looked like birds because those early inventors looked to nature for solutions. But we don't have a model in nature to look to. The sun is not a good model for fusion here on earth. We're having to start from the very beginning."

Cowley says a Manhattan Project for fusion would, of course, greatly speed up its delivery. "ITER will cost around €15bn, but that is not expensive when you consider the prize. At present, all we can hope for is, if oil prices are still high in 2015 and we pull off a big shot demonstrating parity of power, this gets us the international attention – and therefore the funding – we need to really push on. JET was first funded and built during the 1970s due to the oil crisis. That is not a coincidence: there has always been a direct correlation between investment in fusion and the price of oil. Interestingly, though, China is now putting a lot of money into fusion."

This raises another big question: who will stand to benefit financially from its commercialisation? "The global energy market is worth $5-6 trillion a year: somebody will make a lot of money out of this," says Cowley, who predicts that once ITER provides a demonstration model for a fusion reactor all the major countries involved will then attempt to build their own version. "We handed our advantage away with fission. We really don't want to make the same mistake again." One area where the UK already has an edge, says Cowley, is making the very specialised steels required for next-generation tokomaks.

It's hard not to look at the potential of fusion and scream: "We need this right now!" But Cowley says we still face a 30-year wait for the magic day when we flick a switch and electricity generated from fusion flows from the socket. "After ITER, we will then have to build a demonstration plant. We hope to have that built by 2040. This is why there needs to be, in my mind, a 10-fold increase in fission power by 2050. We still need fission because it is a bridging technology until fusion becomes commercial. By 2100, fusion could be producing 20-25% of all our energy." (Romanelli's outlook is a little more optimistic: he believes fusion will be providing 50% of the world's energy by 2100.)

What Cowley is admitting, though, is that as long as fusion research remains underfunded (a term he doesn't utter, but the implication is there) then it will never save humanity from climate change, oil wars and the poverty and underdevelopment caused by ever-higher energy costs. As if to prove his point, he admits that on occasion he has even turned to eBay to buy spare parts for the smaller UK-owned tokamak at Colham which is known as Mast (Mega Amp Spherical Tokamak).

But such things do not deter him from pushing forward as best he can, he stresses. He is first and foremost a plasma physicist.

"Saving the planet is a nice thing to do," he laughs. "Doing something that no one else has ever done is attractive, too. But, ultimately, this is fascinating. I work at the best fusion laboratory in the world, where we conduct day-to-day physics with an incredibly high level of intellectual activity. Every night on the train home I prefer to do a calculation rather than a sudoku. I try to work out things such as how a 200-million-degree-celsius plasma behaves in a magnetic field. Such things are critically important for the future of our world, but they're bloody good fun, too."