Nuclear fusion is a reaction like the type that powers the Sun and other stars. Unlike the nuclear fission underway at our current nuclear plants, fusion generates far more energy without any harmful waste products. Theoretically, fusion reactors are capable of producing nearly limitless energy using nothing but seawater as fuel.
Theoretically. Fusion requires the kinds of temperatures and pressures found inside the cores of stars, and generating those conditions on Earth is extremely difficult, which is why the tech seems perpetually five or ten or twenty years away. Most designs involve giant magnets and lasers and can get complicated, to say the least.
The standard design of fusion reactor is called the tokamak reactor, and it involves a ring of magnets that force the nuclear material to travel in a large circle. The stellerator design used by the W7-X reactor adds several twists to the ring to increase stability.
However, the stellerator design is still relatively untested, so a group of researchers spent the past year studying the W7-X reactor to ensure that it was working the way it was supposed to. They found an incredibly small error rate, less than 1 in 100,000, which the researchers characterized as "unprecedented accuracy."
This is good news for the W7-X reactor, which was intended as a proof-of-concept for the stellerator design. Now that the researchers know the accuracy of the reactor's magnetic fields, they can begin building new reactors that focus on efficiency.
Unfortunately, current fusion reactors, including the W7-X, are still not efficient enough to produce more energy than they use. However, the success of W7-X gives the researchers hope that the next generation of fusion reactors will be able to reach that limit.