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Magnetic Field In Fusion Reactor Mapped With Extraordinary Precision

author

Dr. Alfredo Carpineti

Senior Staff Writer & Space Correspondent

clockDec 7 2016, 11:10 UTC

The field line on the magnetic surface of the stellarator. Nature Communications

Achieving nuclear fusion in the next few decades is an imperative goal for our power-hungry society, and scientists might have just confirmed that we are making the right steps forward.

In a paper, published in Nature Communications, American and German physicists have modeled the complex magnetic field inside the Wendelstein 7-X (W7-X) fusion energy device to a precision of less than one part in 100,000, confirming that the machine is working as designed.

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“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 team wrote in their paper.

Magnetic fields are the cornerstone of nuclear fusion. Since we can’t use gravity to trap hot plasma like stars do, we need to trap the hot material in magnetic fields inside large machines. In there, the hydrogen turns into helium, liberating a huge amount of particles and energy that we can harness.

Many fusion reactors keep the plasma in a donut-shaped magnetic trap. W7-X, instead, is a stellarator where the “donut” is twisted on itself, like a garland. Although not as successful as the more traditional design, which is known as tokamak, the stellarator has several advantages, but it requires a lot more magnets to trap the plasma. This new research shows that the complex magnetic confinement field actually works as expected.

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“We’ve confirmed that the magnetic cage that we’ve built works as designed,” said Sam Lazerson, from the Princeton Plasma Physics Laboratory (PPPL), in a statement.

The team sent electron beams along magnetic field lines and then took cross-sections of the magnetic surface to see where the electrons were going. With this technique, they were able to map the full magnetic field inside the machine.

Stellarators were mostly abandoned in the 70s due to their complexity, but thanks to advances in computing and physics, they are back at the forefront of nuclear fusion research. W7-X is the largest stellarator in the world and the first one to be able to sustain hydrogen plasma, a crucial requirement to create workable nuclear fusion.

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A schematic of the W7-X reactor. C.Bickel/Science


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