A hybrid of two popular nuclear fusion reactor designs could lead to more efficient power plants.
Magnetic confinement fusion reactors use magnetic fields to squeeze a cloud of charged ions, called a plasma, into a tiny volume, which increases the chances of atoms fusing together and releasing energy.
There are two main types of reactor that confine the plasma in different ways. A tokamak, which is the design used by the recently retired Joint European Torus (JET) in the UK, is shaped like a doughnut, with coils of electromagnets wrapped around it. Stellarators are more popular for smaller, modular fusion designs, and instead use a series of twisted and bending coils to confine their plasma.
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Both designs have drawbacks: the plasma inside tokamaks is prone to sudden bouts of turbulence called instabilities, which can damage the reactor or disrupt the fusion process, while stellarators can only contain a relatively small amount of plasma and are complex to build.
Now, and at the Max Planck Institute for Plasma Physics in Greifswald, Germany, have combined both designs into a tokamak-stellarator hybrid. They say it would be simpler to build and could form larger, more stable plasmas than either reactor alone, while also reducing the amount of energy needed to run.
The design looks similar to the doughnut shape of a tokamak, except for additional twisted electromagnetic loops running through its centre, which Henneberg and Plunk call 鈥渂anana coils鈥�. From their simulations, they found that this creates enough 鈥渢wisting鈥� in the magnetic fields to avoid the catastrophic instabilities found in pure tokamaks.
The coils also solve another significant engineering difficulty with tokamaks, says Henneberg, which is the need for a large current moving through the plasma itself to help confine it. The lack of a current both simplifies the design and could save energy, she says.
鈥淭his is really interesting work that uses modern theoretical and computational tools to investigate a new idea in fusion energy,鈥� says at Lawrence Livermore National Laboratory in California. 鈥淚t鈥檚 a conceptual design, so quite far from something that could be built yet, but it鈥檚 a great example of creative theory that could have a big impact on fusion energy if it leads to new designs and experiments.鈥�
Because of the similarity of the design to a tokamak, it might be possible to convert existing tokamak reactors to this new design, says at Proxima Fusion, a stellarator-based start-up based in Germany.
Henneberg and Plunk say they are in talks with several universities to try to build one. 鈥漌e cannot 100 per cent predict with the computational tools we have if you get disruptions or not, so I believe in the end we have to build something to check to be sure,鈥� says Henneberg.
Physical Review Research
