Wendelstein 7-X. A technology step towards demo

The Wendelstein 7-X stellarator, presently under construction in Greifswald, will be the first 'fully-optimized' stellarator device which combines a quasi-symmetric magnetic field configuration with superconducting coils, a steady state exhaust concept, steady state heating at high power and a size sufficient to reach high nTτ-values. W7-X has been optimized numerically by J.Nuehrenberg et al., based on the concept of quasi-isodynamicity. Its key element is an optimized magnetic field configuration, generated by 50 non-planar superconducting coils. It is the mission of this project to demonstrate the reactor potential of the optimized stellarator line. Most of the components have been fabricated already and four out of ten half-modules of the magnet system have been assembled already. This paper presents an overview of the status of construction and a summary of the future developments. (author)