Physics and Engineering Design for Wendelstein VII-X

The future experiment Wendelstein VII-X (W VII-X) is being developed at the Max-Planck-Institut für Plasmaphysik. A Helical Advanced Stellarator (Helias) configuration has been chosen because of its confinement and stability properties. The goals of W VII-X are to continue the development of the modular stellarator, to demonstrate the reactor capability of this stellarator line, and to achieve quasi-steady-state operation in a temperature regime >5 keV. This temperature regime can be reached in W VII-X if neoclassical transport plus the anomalous transport found in W VII-A prevail. A heating power of 20 MW will be applied to reach the reactor-relevant parameter regime. The magnetic field in W VII-X has five field periods. Other basic data are as follows: major radius R₀ = 6.5 m, magnetic induction B₀ = 3 T, stored magnetic energy W ≈ 0.88 GJ, and average plasma radius a = 0.65 m. Superconducting coils are favored because of their steady-state field, but pulsed water-cooled copper coils are also being investigated. Unlike planar circular magnetic field coils, which experience only a radially directed force, twisted coils are subject to a lateral force component as well. Studies of various superconducting coil systems for Helias configurations have shown that the magnitudes of these radial and lateral force components are comparable. Based on a support model, the mechanical stresses are calculated; all components of the stress tensor are of equal importance. Other studies being conducted are concerned with the many complex engineering aspects presented by the construction of nonplanar superconducting coils.