Set the controls for the heart of the Sun



The JET fusion reactor looks more like the lair of a Bond villain than an extraordinary British experiment that might save the world.

This is the view inside the doughnut-shaped JET reactor, the largest fusion device on Earth. During a reaction, nuclear fuels are held away from the walls by electromagnets, and reach temperatures more than ten times hotter than the core of the sun

The highly compacted core of the sun is a very hot place indeed.

In the star's burning heart, hydrogen atoms collide at immense speeds. This welds them together and turns them into helium atoms, which each release a burst of energy that escapes into the solar system as light. It is a nuclear furnace, responsible for fuelling all life on Earth, that consumes a lot of hydrogen (600 million tons every second) at very high temperatures (over 15 million degrees C). As such, it's the second-hottest place in the solar system.

The hottest place? Surprisingly, that's rather closer to home: to be precise, the small English village of Culham, a few miles down the A4074 out of Oxford.



Here, in an innocuous building similar to a Seventies-style concrete university campus, one of the most important experiments in the history of mankind is taking place. If all goes well - and things are going very well - it will solve the problem of meeting the world's energy needs. More power will flow into the world's grids than we'll ever need.



The superheated plasma at the Culham Science Centre

To step into its heart, I don a hard hat and head towards a distant thunder. To enter the mechanism, I have to pass through a metal turnstile and an airlock that says, 'Ensure all doors are sealed before entering reactor chamber.' A guard hands me a radiation badge. 'It will come up with a reading of zero, but we must check,' says Dr Francesco Romanelli, head of the JET (Joint European Torus) reactor. Then we step inside.



The hall within is a Star Wars-style array of towers, pipes and antennae feeding into a 30ft-tall circular machine lined with carbon tiles and surrounded by electromagnets that can generate a magnetic field 100,000 times stronger than Earth's. The machine is the shape of a torus, or doughnut.



Even now, when the reactor isn't burning, you can't enter the chamber itself without a radiation suit. When components inside need replacing, robot arms are used - so sophisticated their operators can 'feel' through the metal fingers. Platforms and stairs surround the central core; on second thoughts, it's less Star Wars and more Moonraker.



Although any sci-fi analogy would do; the experiments being done here have actually been a staple of science fiction for decades, since this type of fusion reactor, the tokamak (see box), was invented by Soviet scientists in the Fifties. And they employ a technology the US planned to use to shoot down nukes as part of the Strategic Defense Initiative - or 'Star Wars' - programme.



After more than half a century, all these grand schemes are becoming reality.



The control room at JET

A view of the machine showing the beam-heating systems

The reactor inside the Culham Science Centre, which is managed by the UK's Atomic Energy Authority, recreates the reaction that occurs at the heart of the sun, only more intensely. Here, less than a gram of hydrogen is used, but it's heated to 200 million degrees C by high-energy beams that are among the most powerful and lethal heating devices on Earth.

On start-up, when two 50ft white towers aim their barrel-sized particle cannons into the reactor, will it explode into a fireball and swallow our planet like a lump of coke in a blast furnace? Happily, no. When the reactor burns, the hydrogen becomes so hot that no physical container can cool or hold it; so the intense magnetic field holds the swirling vortex of superheated hydrogen in place. The reacting material is completely invisible - it radiates energy at frequencies the human eye can't see - but as the reactor heats, sections of the wall become so hot that the tiles glow red.



'This is save-the-world science. This is the energy holy grail'





Meanwhile, the incredibly intense particle beams consist of uncharged atoms flying at more than ten million metres per second. They would instantly vaporise anyone who stood in front of them. Even metal components melt in microseconds if they get in the way of the beams. So the towers are cooled with liquid helium, as well as water - 4,000 cubic metres are pumped through the system every hour.

And what's it all for? Simply, the experiments at JET could pave the way for a scientific achievement on a par with putting a man on the Moon. JET has been able to initiate nuclear fusion at the touch of a button for decades - but the energy put in has always outweighed the energy harvested from the reactor.

Now, though, it's being used as a test bed for a new reactor, ITER, which will generate electricity from fusion, using fuel found in ordinary seawater. Just one cubic kilometre of seawater contains enough deuterium - used as a nuclear fuel by JET - to generate more power than the world's entire oil reserves.

An employee operates the robot arms used to replace internal components (left) while another examines the far infra-red lasers



When a fusion plant eventually manages to return more energy than is put in, wind and solar energy will become almost irrelevant. Countries whose power and wealth are built on reserves of fossil fuels will find themselves in a very different situation.

It might sound too good to be true - and even the most optimistic fusion physicists accept that working fusion power stations are at best more than three decades away. But by then supplies of oil and gas may have run out altogether. For a species whose appetite for energy shows no sign of abating, this reactor might be the only hope. Does the answer to all Earth's power problems lie inside this machine?

Britain is, effectively, an 80-gigawatt appliance - that's what it takes to fuel us. But finding the required energy is getting harder. In ten years' time, we'll have to import up to 90 per cent of our gas, compared to 30 per cent two years ago, and ageing power plants that currently supply a third of our electricity will have to be shut down.

Three years later, all but one of our nuclear plants will have been decommissioned. By 2050, most forecasts say the world's oil reserves will have been exhausted, with gas and coal running out shortly after.



While wind and solar power are mooted as solutions to the energy crisis, it's by no means clear they can supply energy reliably at national-grid level - ever. On the plus side, we are planning to build new nuclear power stations, but they can only give us 20 gigawatts.



The centre is located near Oxford

The last time things looked so bleak was in the Seventies --coincidentally, another period when nuclear fusion was in vogue.



'There is an interesting study --the amount of resources devoted to researching fusion is related to the price of oil,' says Dr Romanelli.



'When the price of oil goes up, they spend money on fusion; when the price of oil goes down, they tend to forget about other energies. In the Seventies, during the two oil crises, there was investment in fusion - that was why JET was built.



'In the Eighties, it decreased. The energy market in Europe is worth 700 billion euros a year. The amount spent on energy research is two billion a year - almost nothing. Overall, 0.01 per cent of the global energy budget is spent on fusion research. More money is spent researching new cars.'



Now JET is laying the groundwork for the new reactor, ITER, to be operational by 2018. ITER has become the biggest joint science project since the International Space Station. It will cost ten billion euros and Britain has committed almost half of its energy-research budget to the programme.

One of the towers that fires neutral particle beams into the reactor

Currently, every nuclear reactor operating on Earth is a fission reactor - using energy released when heavy atoms such as uranium decay into smaller atoms, a process similar to the one used in the first nuclear weapons. A fusion reactor works in the opposite way, harvesting the energy released when two smaller atoms combine, releasing a fast moving subatomic particle.



This reaction is used in hydrogen bombs, triggered by setting off a normal fission-based bomb of the sort dropped on Hiroshima - but it's uncontrolled, and over in an instant.

In a working fusion reactor, the reaction will be sustained, and safe. The fast-moving particles released by the hydrogen will be 'caught' in a blanket of liquid lithium, which will heat up, in turn boiling water and driving steam turbines as found in a conventional nuclear or coal power station.



But there are several huge differences. No carbon dioxide is emitted from a fusion reactor. The fuel is found in ordinary water - there are 25ml of deuterium in every litre you drink. And there's no chance of a fusion Chernobyl.



The reaction is so difficult to sustain that it can't run out of control. And while the reactor tiles become mildly radioactive, they're far less toxic than the waste generated by normal fission reactors, and become totally safe in 100 years. There is no weapons-grade fuel for terrorists to steal.

Remote handling practice with Jenga blocks (left) and the button used to cut power to JET in an emergency



So far, JET, the most advanced and largest fusion reactor on Earth, is only efficient enough to return 65 per cent of the power put into it, and can only sustain the reaction for a few seconds. But if Culham's simulations are accurate, ITER will produce up to ten times the amount of energy put in, for periods of more than 400 seconds.



Dr Romanelli explains: 'The ITER machine is not that far beyond what we've built at JET. It will be about eight times the volume, and about three times the power - that makes us confident we will achieve what we want.

'Our goal is to reach a point of break-even, where the energy we get out is equal to the energy put in. All our research, and our work with other reactors like this, has shown that it's simply a matter of scale. Our machine is now fully devoted to testing design choices for ITER.



'This October, we will shut down the reactor and remove its carbon tiles, to install new beryllium tiles on the wall and tungsten tiles on the floor, where most of the heat escapes from the chamber. If we are able to demonstrate this works, ITER will perhaps begin being built at an earlier stage.'



John Parris of HiPER - another European project, which will investigate laser-driven fusion - says: 'This is save-the-world science. Fusion is the only serious answer to future energy demands - this is the energy Holy Grail. The human race has a massive, ravenous demand for power, and there is no other way to provide grid-level energy.'



Dr Romanelli's team have already proved man can recreate the centre of the sun on Earth. If their calculations are correct, JET is the seed of an idea that will solve the energy crisis forever, halt global warming and ensure nations never have to battle over energy sources again.

The downside? It'll take billions of pounds, and more than three decades, to find out.





Watch the JET Fusion Reactor in action





POWERING THE FUSION REACTOR

A tokamak fusion reactor (the name is a loose transliteration of the Russian phrase 'TOroidal CHAmber with MAgnetic Coils') heats two forms of hydrogen atoms - deuterium and tritium - up to temperatures far hotter than the centre of stars, containing the dangerous mixture in a circular magnetic field 100,000 times stronger than Earth's.



Both fuels are heavier forms of hydrogen - deuterium is found naturally in seawater, and tritium, which is mildly radioactive, is created as a by-product of fusion reactions, or inside fission reactors.



Just tiny amounts of the fuels - at JET, less than a gram - are used inside a tokamak, heated by neutral beams (uncharged streams of atoms fired at more than ten million metres per second), microwaves and electrons until they reach around 200 million degrees C.



Electromagnets on the outside of the reactor contain the mixture in a doughnut shape - in the JET reactor, copper electromagnets are used, but in ITER, its European successor, liquid-helium-cooled superconducting magnets will be used, which allow electricity to circulate without losing any power.



At this temperature, the hydrogen forms a plasma - the fourth state of matter after solid, liquid and gas. Plasmas are found everywhere on Earth inside neon lights, but inside a tokamak, the deuterium-tritium mixture is superheated and subjected to a huge electric current so that the natural repulsive forces between atoms are reduced.



When deuterium and tritium atoms collide in this state, they can form a helium atom - and release energy in the form of a single neutron moving at incredibly high speed. Because the neutron is uncharged, it escapes the tokamak's magnetic field and is 'caught' in a blanket of lithium (a light metal) that surrounds the reactor.



The heat generated causes the lithium to heat up - and in a commercial reactor, this would in turn be used to boil water, which would then drive steam turbines and generate electricity, as in a normal nuclear fission or coal power station. The by-product of neutrons striking lithium atoms is tritium - which, in a commercial reactor, will be recycled to be used as fuel.







