Wendelstein achieves ultra-precise magnetic topology

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Wendelstein achieves ultra-precise magnetic topology

A recent article in the online journal Nature Communications confirms that the complex topology of the magnetic field of Wendelstein 7-X—the world's largest stellarator—is highly accurate, with deviations from design configuration measured at fewer than 1-in-100,000.

To measure the magnetic field, the scientists launched an electron beam along the field lines. They next obtained a cross-section of the entire magnetic surface by using a fluorescent rod to intersect and sweep through the lines, thereby inducing fluorescent light in the shape of the surface. (Click to view larger version...)
To measure the magnetic field, the scientists launched an electron beam along the field lines. They next obtained a cross-section of the entire magnetic surface by using a fluorescent rod to intersect and sweep through the lines, thereby inducing fluorescent light in the shape of the surface.
In the complex shape of a stellarator, high engineering accuracy is needed because even the smallest magnetic field errors can have a large effect on the magnetic surfaces and the confinement of the plasma.

Wendelstein 7-X relies on a system of 50 non-planar and superconducting magnet coils to create a precisely shaped magnetic "cage" to confine the plasma for discharges of up to 30 minutes (projected). Following a first helium plasma in December 2015 and an initial hydrogen campaign with over 2,000 plasma pulses, the machine is now being prepared for high power operation at the Max-Planck-Institute für Plasmaphysik (IPP) in Germany.

Because a carefully tailored topology of nested magnetic surfaces is necessary for optimum confinement, the study's highly sensitive measurements provide welcome proof that such a topology is feasible and verifiable with the required accuracy.

Read the original article in Nature Communications.
Other reports at IPP and the Princeton Plasma Physics Laboratory, PPPL.


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