Fusion energy inches toward ignition
US breakthrough as more energy released than supplied to the fuel to start the reaction. James Mitchell Crow reports.
The dream of clean, low carbon, near-limitless electricity just edged a little closer to reality. Researchers in the US have finally succeeded in releasing more energy from a fusion reaction than the energy they had to supply to the fuel to get the reaction started. It’s a significant milestone on the road to self-sustaining fusion reactions in future power stations.
As Cosmos recently reported in an investigation of fusion's possibilities, two major research efforts are currently underway to harness its power. Both aim to capture the energy released when deuterium and tritium ions, heavy forms of hydrogen, are forced to fuse under enormous temperatures and pressures. But the approaches they take are very different.
One, the international ITER project, aims to contain this white-hot reaction within a magnetic chamber. The other, the US National Ignition Facility (NIF), aims to kick-start and then contain the reaction by firing 192 powerful lasers at a peppercorn-sized tritium-deuterium fuel pellet. It is the NIF group that made the latest breakthrough, publishing its findings in Nature.
The announcement should ease some of the pressure building on the team. When the NIF opened in 2009, expectations were high. Researchers ambitiously aimed to achieve ignition – a self-sustaining fusion reaction – by the end of 2012. In fact, they fell far short. So last year, NIF researchers reset their sights on more modest goals. Their first key goal has now been met.
“This is a truly excellent paper that begins to get at the core problems that NIF has – instability of the capsule containing the fusion fuel as it is compressed by lasers,” says Steve Cowley, director of the Culham Centre for Fusion Energy in the UK.
When attempting to achieve ignition, the team had been unable to control the reaction to compress the pellet evenly. “The implosion was tearing itself apart,” explains Omar Hurricane, from the Lawrence Livermore National Laboratory in California, who led the latest research. As a result, energy returns were poor. The team has now found that by boosting laser power at the start of the pulse, the implosion is more stable, releasing 10 times the energy previously achieved.
“We took a step back, and it has given us a leap forward in what we have been able to accomplish,” Hurricane says.
The team is now working to increase implosion speed to move closer to the ultimate goal, ignition.
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