A team of researchers from the US and Germany have now confirmed that the Wendelstein 7-X (W 7-X) stellerator is producing the super-strong, twisty, 3D magnetic fields that its design predicted, with “unprecedented accuracy”. The researchers found an error rate less than one in 100,000.
“To our knowledge, this is an unprecedented accuracy, both in terms of the as-built engineering of a fusion device, as well as in the measurement of magnetic topology,” the researchers write in Nature Communications.
W 7-X isn’t actually intended to generate electricity from nuclear fusion – it’s simply a proof of concept to show that it could work.
In 2019, the reactor will begin to use deuterium instead of hydrogen to produce actual fusion reactions inside the machine, but it won’t be capable of generating more energy than it current requires to run.
That’s something that the next-generation of stellerators will hopefully overcome. “The task has just started,”
The field lines making up a magnetic surface are visualized in a dilute neutral gas, in this case primarily water vapor and nitrogen (pn≈10−6 mbar). The three bright light spots are overexposed point-like light sources used to calibrate the camera viewing geometry.
Some representative nested magnetic surfaces are shown in different colours in this computer-aided design (CAD) rendering, together with a magnetic field line that lies on the green surface. The coil sets that create the magnetic surfaces are also shown, planar coils in brown, non-planar coils in grey. Some coils are left out of the rendering, allowing for a view of the nested surfaces (left) and a Poincaré section of the shown surfaces (right). Four out of the five external trim coils are shown in yellow. The fifth coil, which is not shown, would appear at the front of the rendering.
Fusion energy research has in the past 40 years focused primarily on the tokamak concept, but recent advances in plasma theory and computational power have led to renewed interest in stellarators. The largest and most sophisticated stellarator in the world, Wendelstein 7-X (W7-X), has just started operation, with the aim to show that the earlier weaknesses of this concept have been addressed successfully, and that the intrinsic advantages of the concept persist, also at plasma parameters approaching those of a future fusion power plant. Here we show the first physics results, obtained before plasma operation: that the carefully tailored topology of nested magnetic surfaces needed for good confinement is realized, and that the measured deviations are smaller than one part in 100,000. This is a significant step forward in stellarator research, since it shows that the complicated and delicate magnetic topology can be created and verified with the required accuracy.