The magnet system of Wendelstein 7-X. Fifty superconducting magnet coils create the magnetic cage for confining the plasma. In the twisted coil forms, computational optimization has taken shape. Credit: IPP
One of the most important optimization goals underlying the Wendelstein 7-X fusion device at Max Planck Institute for Plasma Physics (IPP) in Greifswald has now been confirmed. An analysis by IPP scientists in the journal Nature shows: In the optimized magnetic field cage, the energy losses of the plasma are reduced in the desired way. Wendelstein 7-X is intended to prove that the disadvantages of earlier stellarators can be overcome and that stellarator -type devices are suitable for power plants.
The optimized Wendelstein 7-X stellarator, which went into operation five years ago, is intended to demonstrate that stellarator-type fusion plants are suitable for power plants. The magnetic field, which encloses the hot plasma and keeps it away from the vessel walls, was planned with great theoretical and computational effort in such a way that the disadvantages of earlier stellarators are avoided. One of the most important goals was to reduce the energy losses of the plasma, which are caused by the ripple of the magnetic field. This is responsible for plasma particles drifting outwards and being lost despite being bound to the magnetic field lines.
Unlike in the competing tokamak-type devices, for which this so-called “neo-classical” energy and particle loss is not a major problem, it is a serious weakness in conventional stellarators. It causes the losses to increase so much with rising plasma temperature that a power plant designed on this basis would be very large and thus very expensive.