Friday, October 30, 2015

A twisted, racetrack-shaped torus to generate and confine a plasma: the stellarator

A stellarator is a nuclear-fusion device invented in the early 1950s by American astrophysicist and plasma physicist Lyman Spitzer (1914-1997) [1,2]. The name of this complex device signifies a star machine, referring to the goal of harnessing the energy like a stellar object such as the sun. Therefore, this device is also called by the composed term stellarator-heliotron and the concept behind its design is named the stellarator-heliotron concept [3]—heliotron literally meaning sun automat.

In the plasma physics community a stellarator is also known as the black horse of reactors, since it is very difficult to build. It took 1.1 million construction hours (spent over 19 years, including times of construction setbacks) to built the world's largest experimental stellarator, the W7-X, which currently is ready to be fired up [4].

W7-X is short for Wendelstein 7-X, referring to the Wendelstein mountain in the Bavarian Alps south of Garching, where its predecessor Wendelstein 7-AS was built and tested [5]. The successor W7-X was assembled by researchers and engineers at the Max-Planck-Institut für Plasmaphysik (IPP) in Greifswald, northeast Germany. Now being completed, W7-X—with large modular superconducting coils enabling steady-state plasma operations—is the world's largest fusion device of the stellarator type [5]:
Its objective is to investigate the suitability of this type for a power plant. It will also test an optimised magnetic field for confining the plasma, which will be produced by a system of 50 non-planar and superconducting magnetic coils, this being the technical core piece of the device.
W7-X is expected to generate its first plasma at the end of this year.

References and more to explore
[1]  National Aeronautic and Space Administration: Lyman Spitzer, Jr. [].
[2] Encyclopaedia Britannica: Lyman Spitzer, Jr. [].
[3] Energy technology Network: Stellarator-Heliotron Concept [].
[4] Yahoo!: Germany is about to start up a monster machine that could revolutionize the way we use energy [].
[5] IPP: Wendelstein 7-AS (1988-2002) [].
[6] IPP: Wendelstein 7-X [].

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