Researchers have successfully tested a new 拢55-million nuclear fusion machine in the UK, which could provide vital insights for a future prototype power station.
The at the Culham Centre for Fusion Energy in Oxfordshire took seven years to build. Today, the machine produced its first plasma, the state hydrogen reaches when heated to extremely high temperatures.
Our understanding of how stars are powered by hydrogen fusing into helium dates back around a century, but efforts to harness clean energy from the reaction in a commercial power station still face many barriers 鈥� not least how to extract more energy than we put in.
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One key problem is the heat from the plasma, which reaches millions of 掳C. This means it gradually burns away the exhaust system that extracts heat from the tokamak, the machines in which the fusion reaction occurs, with the plasma held in place by an electromagnetic field. In a power station, that could mean replacing the exhaust every three years or so, an unacceptable interruption and cost for a commercial plant.
The MAST Upgrade team hopes to crack the dilemma by using a new type of exhaust called a 鈥渟uper-X diverter鈥�. It works by sending the plasma a long distance around the machine and across a wider area than usual, reducing the heat density so that it cools before being extracted.
Ian Chapman at the UK Atomic Energy Agency, the parent body for the project, says the design could reduce the heat by 10 times, akin to taking temperatures facing a spacecraft entering Earth鈥檚 atmosphere down to that of a car鈥檚 engine.
Juan Matthews at the University of Manchester, UK, says designing a diverter that doesn鈥檛 need regular replacement is a big issue, but only one of many. 鈥淚t鈥檚 just one of the huge number of problems that are going to have to be solved before a [fusion] power system is built.鈥�
A different shape
Most tokamaks are doughnut-shaped, but this one is spherical with a thin column in the middle rather than a larger empty space, producing a plasma shaped like a cored apple.聽The design has an improved geometry 鈥� the magnets crucial to controlling the plasma are closer to it. But the issue of managing heat in a smaller space is one key drawback compared with conventionally shaped tokamaks.
Around 90 per cent of the Culham machine is new. The rest 鈥� primarily the building and steel 鈥渧accum vessels鈥� that contain the plasma 鈥� was salvaged from the original MAST, which ran from 1997 to 2013. The first plasma produced is about two years later than planned and the machine is over budget, but Chapman says that is unsurprising given how hard the technical challenge is.
The new facility will operate at 鈥渘ear-fusion鈥� conditions of 50 to 100 million 掳C, which is hotter than the sun. By comparison, the world鈥檚 biggest fusion project, ITER in southern France, aims to produce plasma in 2025 at 150 million 掳C. In July, ITER .
Researchers at the Culham Centre for Fusion Energy are also continuing work on a major experiment on an existing tokamak called the Joint European Torus (JET). The JET team had planned to attempt a fusion of two hydrogen isotopes, deuterium and tritium, in November this year.
It would have been the first operation of its type since 1997, and the team had hoped it would hold a plasma to several seconds, far longer than the milliseconds achieved last century. However, covid-19 lockdowns and restrictions have delayed the operation to next year.
Findings from MAST Upgrade will benefit ITER and the UK鈥檚 , a prototype fusion power plant ambitiously pencilled in for completion by 2040. One way that MAST will help ITER is by providing more observational data that will help corroborate models trying to extrapolate data from JET to ITER.
