Nature reported experiments that have succeeded in releasing more energy through a fusion reaction than is absorbed by the fuel, marking an important step towards nuclear fusion as a viable alternative energy source.
Professor Steve Cowley, Director of the Culham Centre for Fusion Energy, said:
“This is a truly excellent paper that begins to get at the core problems that NIF (the National Ignition Facility) has – instability of the capsule containing the fusion fuel as it is compressed by lasers.
“At the moment the situation is that if they push the laser hard enough to get ignition the capsule will become unstable so the best energy yield is from pushing less. There are two possible solutions: (1) a bigger laser pushing slowly (but if the laser is too big the capsule explosion is too big to be useful!); (2) an innovative capsule that can be pushed hard and still remain roughly stable. Livermore should be given plenty of time to develop a better capsule – it strikes me that we have only just begun to understand the fusion regime.
“The different measures of success make it hard to compare NIF’s results with those of ‘magnetic confinement’ fusion devices such as JET (Joint European Torus). In 1997 JET made 16MW of power with 24MW into the device – approaching break-even. In principle better than NIF. But NIF is just beginning to understand what they need to do. We have waited 60 years to get close to controlled fusion, and we are now close in both magnetic and inertial confinement research. We must keep at it. The engineering milestone is when the whole plant produces more energy than it consumes – ITER, the successor to JET, will be the first experiment to do this. ITER is going slowly but progress is happening.”
There are two main approaches to fusion research. One is ‘inertial confinement’, using lasers to compress fuel pellets, which triggers fusion reactions (as at NIF). ‘Magnetic confinement’ is the other approach, putting plasma in a magnetic container and heating it up till nuclei fuse; this is what happens at Culham, notably on the JET device, and in the future on the larger ITER project in France. Both approaches are aiming for an energy gain from fusion and for ‘ignition’ – the point at which fusion reactions become self-sustaining and can therefore be harnessed as a practical source of energy for future power stations.
‘Fuel gain exceeding unity in an inertially confined fusion implosion’ by Hurricane et al. published in Nature on Wednesday 12 February.