Sun-in-a-box: The shiny heat-resistant beryllium-coated interior of the JET (Joint European Torus) fusion reactor in Oxfordshire, England. Temperatures within the plasma can reach up to 100 million ºC - hotter than the core of the Sun.
Credit: JET/EFDA
No device on this scale has ever been planned before, however. ITER will have a huge central chamber, capable of holding about seven times more plasma than any fusion reactor built before it. Coated with beryllium and tungsten, it will glow eerily during its 24-hour-a-day operation as hydrogen is fused into helium in a ghostly mimicry of the forces that sustain and light the Sun. Putting together a machine like that is not a business for the faint-hearted. Nevertheless, Holtkamp is unperturbed about dabbling with such potent forces.
“There will be tricky moments, particularly when the main plasma chamber and the superconducting magnets that will contain the super-hot hydrogen atoms are put together,” he says. “However, we will take it all very slowly and very carefully.”
Intriguingly, the construction of these two key components has been shared out evenly among the members of ITER. The chamber will be the handiwork of Russia, Korea and Europe, for example, while the building of the magnets will be shared between all seven participants in the collaboration. No one nation will be allowed to dominate any single area of expertise in construction. As an effort in scientific cooperation alone, ITER is certainly ambitious.
Finally, when the last pieces are joined, the machine will be covered in a giant, white, hangar-like structure that will be clearly visible from the main Marseilles road that sweeps through Cadarache. There will be no globular containment vessel like those that give nuclear power plants their distinctive look, nor cooling towers that typify fossil fuel plants. ITER may be a fantastic concept but it is going to look distinctly boring.
It is a strange combination – high-tech science with low-rent architecture. But then fusion itself is a rather odd concept. The standard fission reactors in operation at nuclear plants today use fuel made up of large atoms, like uranium. When encouraged to break apart, these atoms release energy. But fusion works in reverse. Light atoms are coalesced to make heavier ones, and in the process energy is released. The basic fuel for this task is the hydrogen atom, while the product is the helium atom – and bountiful energy.
Christopher Llewellyn-Smith, head of Europe’s Joint European Torus reactor (JET), based at the Culham laboratory in Oxfordshire (currently the biggest fusion reactor in the world – see image bottom left for a glimpse of it in action), outlines the basic physics: “The nucleus at the heart of the helium atom is the most tightly bound of all nuclei in nature. It takes enormous energy to rip it apart. The logical corollary of that observation is that when you put a helium nucleus together from smaller components, you will liberate huge amounts of energy.”
This process only occurs when the nuclei of the atoms are in very energetic states, however. Heated to 100 million degrees Celsius, they barge into each other at such colossal energies that the electrical repulsion, which normally prevents them from interacting, is overcome. Nuclei are pressed together, up close and personal, and fuse – producing neutrons and a great quantity of pent-up energy. A total of 17.6 million electronvolts is released during an individual fusion reaction. This compares with the one electronvolt produced by a typical chemical reaction – for example, by the oxidisation of a carbon atom, the basic process that underpins the burning of fossil fuel.
Recreating the fusion process clearly offers great rewards, but it is not an easy task – to say the least. In particular, the business of containing a cloud of plasma that has been heated to around 100 million degrees Celsius has taxed the imaginations of a great many scientists. You can’t hold super-hot matter in an old bathtub, after all. In the end, it took the ingenuity of Russian scientists Igor Tamm and Andrei Sakharov, working at Moscow’s Kurchatov Institute in the late 1950s, to come up with the answer: the tokamak.
The key feature of a tokamak is its central chamber which is shaped like a giant, hollow doughnut or torus, and which gives the device its name. Abbreviating the Russian ‘TOroidalnaya KAmera v MAgnitnykh Katushkakh’ results in ‘tokamak’, or its similar English equivalent, TOroidal CHAmber in MAgnetic Coils (tochamac). Powerful electric currents are passed through coils that wind round the doughnut-shaped chamber and through the plasma inside it, creating a twisting magnetic field that holds the super-hot plasma in a tight, invisible grip.
However, massive amounts of electricity are needed to create this unseen container, and to date, far more energy has been spent powering-up tokamaks than has been released through the resulting fusion of atoms. For example, JET soaks up 25 megawatts of electrical power to generate only 16 megawatts of fusion power. However, ITER – which will be the biggest tokamak reactor ever built when completed – is scheduled to have an output of 500 megawatts for an input of only 50 megawatts of electricity.
Once a tokamak’s magnetic field is switched on, and air is pumped out of its central chamber, small amounts of the hydrogen isotopes tritium and deuterium are inserted. Then an electric current is driven through the gases, heating them up to about 30 million degrees Celsius. At this temperature, electrons are stripped from their orbits around the atomic nuclei, producing a soup of basic particles. Finally this plasma is heated even further, to about 100 million degrees Celsius, either by bombarding it with highly energetic particles or by injecting microwaves. At this temperature, deuterium and tritium nuclei in the reactor begin to fuse to create helium and neutrons.
Importantly, of the 17.6 million electronvolts of energy created with each reaction, most of it – about 14 million electronvolts – is transferred to the neutron. It has no charge and cannot be contained by the tokamak’s magnetic field. So it whizzes out of the reactor and smashes into the atoms of the reactor wall, transferring its considerable kinetic energy to them. The end product is heat, which can then be used to drive turbines.
And other approaches to fusion?
Fascinating article and it's nice to renew the feeling of optimism that has characterized the fusion program for so long. I do hope it works if for no other reason than to act as a step towards what will ultimately be the most widespread source of non-solar derived energy on the planet, doing for energy what the micro-processing and the silicon chip did for computational memory; making it, at long last, almost too cheap to meter.
I would have appreciated hearing a little bit about the burgeoning research in Inertial Electrodynamic Confinement (IEC) fusion which is being carried out now at many locations both academic and private research. The issues of containment of hot plasma seem to be bringing into focus the meaning of "hot" when describing velocities that approach the speed of light, which some thin IEC fusion may be effective at addressing whereas the large Tokomaks will not.
One researcher speculated that the reason the old USSR researchers gave the west the key elements of their research was not to further the research but to permanently hobble the west's research in fusion which up until that time had been through the work of Philo T. Farnsworth and Robert Hisch using high speed electron guns and magnets and a still rudimentary understanding of the problems they were encountering.
Even the rosiest estimates to break even still leave a lot of progress to be made before the Tokomak can ever be made even as portable as a modern day large scale electrical generator, and will initially require a huge outlay in infrastructure to apply its output. The IEC's approach forsees smaller and more ubiquitous, and non-radioactive, processes. Worth looking up the term Polywell Fusion for those interested.
Another alternative
Take a look at another alternative approach to fusion, which might prove cheaper, cleaner, more efficient, simple and easilly reachable.
At http://www.focusfusion.org
Same thing but cleaner !
So, what happens once you have fused all the Hydrogen on the planet to Helium ? Does not seem renewable in the long term. But maybe that will be the next generations problem .....
not really a concern
Since Hydrogen is by far the most abundant element in the universe, can be produced from water, and only small amounts are needed to fuse in order to release large amounts of energy; there no risk of running out of hydrogen within the lifetime of the planet.
Society
The problem with our society is that we spend trillions on wars, financial schemes, websites, lawyers, and other crap. There's no resources left to advance science. If we spent on science half of what we spent on sports or religion or politics, we'd solved sustainable nuclear fusion a long time ago.
Hell, we do everything we can to discourage people from entering sciences and engineering. From outsourcing jobs to arresting paleontologists for discovering a T-Rex skeleton.