Harnessing the energy released in nuclear fusion reactions is a neat idea, but it's extremely difficult to realize — even a prototype fusion reactor producing net energy is still a long way off. Yet, the completion of Wendelstein 7-X (W7-X), a state-of-the-art experimental fusion device in the north of Germany, and recent tests of its magnetic-field topology reported by Thomas Pedersen and colleagues (Nat. Commun. 7, 13493; 2016) are important steps towards producing energy from fusion.
W7-X is a stellarator, one of two standard types of machine capable of sustaining a hot plasma, for which temperatures of around 108 K are needed to spark fusion reactions. Just as in a tokamak, the more common type of fusion reactor, the charged particles of the plasma are confined by means of a magnetic field. In a stellarator, this field is solely generated by external current coils, whereas a tokamak additionally relies on the field created by the moving plasma particles. In principle, stellarators are more stable and offer steady-state operation, but these advantages come at a high engineering price: optimizing the highly complicated layout of the coils, building them and checking the produced magnetic fields are extremely challenging. Hence, tokamaks have afforded better progress in magnetically confining plasmas — less stable, but easier to build.
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