One Step Closer to Fusion Power

The goals of ITER are ambitious. The project aims "demonstrate the scientific and technological feasibility of fusion power for peaceful purposes" by building the first fusion reactor "to produce more power than it consumes." As I've discussed before, while fusion holds great promise, the obstacles it faces are daunting.

Wednesday's Guardian describes the project and its potential role in helping society curb its carbon dioxide emissions:

There is a deafening, unearthly howl as if a jumbo jet was firing up its engines in the Albert Hall. On the screen in the control room a ghostly pinkish glow whips round the edges of the inside of the nuclear reactor. At its core it is 10 times hotter than the centre of the sun.

This, according to some physicists, is the solution to the energy crisis - a future with cheap, reliable, safe and nearly waste-free power. Today, after years of false starts and political wrangling dating from the cold war, they will get their chance to make that dream a reality. A €10bn (£7bn) project, called Iter, to build a prototype nuclear fusion reactor will be signed off in Brussels by the EU, Japan, China, South Korea, India and the US.

The prospect of virtually limitless energy is not merely science fiction. The haunting, screaming growl of matter being smashed together at unimaginably high speed is a daily occurrence at Jet in Oxfordshire, an existing experimental fusion reactor. Jet is by far the biggest of the world's 28 fusion reactors. It is the work of scientists here that has paved the way for the much bigger Iter, which, once the project is ratified in December, will be built in Cadarache in southern France.

Its advocates say nuclear fusion is the most promising long-term solution to the energy crisis, offering the possibility of abundant power from cheap fuel with no greenhouse gases and low levels of radioactive waste. But critics say the government is gambling huge sums of money - 44% of the UK's research and development budget for energy - on a long shot with no guarantee of ever producing useful energy.

The fusion reactor works by using a powerful magnetic field to concentrate the incredibly hot plasma where the reaction occurs. Monday's Nature News describes the perils of this approach as well as a potential solution:

Part of the problem with building a reactor is that the fusing hydrogen gas, called plasma, becomes so hot that it will melt the walls of any machine. The preferred solution is to suspend the plasma in a donut-shaped magnetic field. This field is designed to keep the hot gas away from the walls of the machine, and to squeeze the plasma tightly to increase the chance of atoms colliding.

But as the magnetic donut squeezes, the pressurised plasma becomes more likely to burst out, says Todd Evans, a physicist at General Atomics in San Diego, California. "Think of squeezing a balloon full of water," he says. "The harder you squeeze, the more the balloon bulges out through your fingers."

Eventually the plasma will burst through the field's weakest point. In ITER, a single such burst could release enough power to briefly light one million 100 W lightbulbs, corroding key reactor parts.

Until now, reactor designers have lived with these discharges, but Evans and his team found a way around the problem. The group modified the DIII-D tokamak reactor at General Atomics so as to introduce chaotic static into the magnetic field around the plasma.

This weakens the field just enough to let a little bit of plasma leak out through the bottom, relieving some of the pressure in the system and preventing it from bursting. "It's kind of a beautiful concept," Evans says.

In light of these findings, scientists are now pushing ITER to incorporate this controlled leakage into the design of its fusion reactor, but they may face an uphill battle, as reported in today's edition of Nature (subscription required):

he idea, which has been published in Nature Physics, could help ITER to succeed more quickly. But it comes at a cost: the technique would probably require expensive superconducting coils to be placed near or inside the containment vessel, where space is limited and punishing radiation wears out equipment quickly.

ITER researchers are now mulling over how to work such a breakthrough into the design, which originated more than 20 years ago and has already been through several iterations. The change will have to wind its way through several review committees before receiving final sign-off by designers in the countries funding it: the United States, the European Union, Japan, the Russian Federation, India, China and South Korea. It will also compete with other ideas in the field that could help prevent violent disruptions in the machine or extend the time it can hold fusing plasmas.

Trying to get scientists and engineers to decide which changes to include in the final design and which to save for 'upgrades' isn't going to be easy, says Ned Sauthoff, a physicist at Princeton Plasma Physics Laboratory in New Jersey and head of ITER's US team. "ITER is not just a physics experiment, it's also an experiment in large-scale project management."

The final design should be released within the next couple of years, and it should be interesting for a variety of reasons, including to see whether these new findings are taken into account.