(FT/1-4) The Construction of the Wendelstein 7-X Stellarator
1) Max-Planck-Institute for Plasma Physics, EURATOM Association, Greifswald, Germany
Abstract. This paper reviews the recent progress in the construction and assembly of the large, superconducting stellarator device Wendelstein 7-X in Greifswald, Germany. Technical solutions are discussed as well as the impact on the later physics program. Also the “lessons learned” during the long construction phase are discussed. Last not least, the role of Wendelstein 7-X in the international stellarator program and its relevance for ITER are outlined. Wendelstein 7-X is a large (30 m-3 plasma volume) stellarator with superconducting modular magnetic field coils (3 T induction on axis). The design of Wendelstein 7-X is based on the quasi-isodynamic concept. The mission of W7-X is to demonstrate the basic reactor suitability of this concept under steady-state operation conditions. The project has experienced a number of technical set-backs, in particular in the area of superconducting coils and the mechanical structure of the device. Both problem areas are now solved and the manufacturing of component progresses well. In particular, all magnetic field coils are manufactured and more than half have already passed the cold test. The project now orients towards device assembly. The device consists of five almost identical modules forming the torus. Each two half magnet modules are assembled in parallel and joined after completion. This important step was recently accomplished by the project in schedule. A large variety of assembly technologies have been developed and successfully qualified. They will be reviewed in the present contribution. The first step in the future operation of Wendelstein 7-X is to develop integrated discharge scenarios with competitive performance parameters in terms of equilibrium, stability and transport. Reference discharge scenarios will be developed with a simplified (inertially cooled) robust test-divertor. After this first (short) operation phase, the pressure-cooled system of in-vessel components is completed and the best-suited discharge scenarios are extended to steady-state (30 min) at full 10 MW ECRH heating power. Local current drive by ECR waves will be used to control the edge magnetic field structure, required for proper divertor operation. A main task is the full integration of discharge scenarios, plasma heating, control and plasma-wall interaction to achieve reactor-relevant plasmas under steady-state conditions.
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