Speaker
F. Warmer
(Max Planck Institute for Plasma Physics)
Description
One of the high-level missions of the European Roadmap to the realisation of fusion energy is to bring the HELIAS stellarator line to maturity. The near-term focus is the scientific exploitation of the Wendelstein 7-X experiment in order to assess stellarator optimization in view of economic operation of a stellarator fusion power plant. W7-X will play a decisive role for these studies but may be too small to explore all issues related with a burning-plasma in 3D geometry. Therefore, an intermediate-step burning-plasma stellarator appears prudent to mitigate the risks which would otherwise arise from the incomplete physics basis. A decision on the necessity of a burning-plasma experiment, however, must await the results of high-performance steady-state operation of W7-X and the fusion phase of ITER.
However, in preparation of this review-point and as a starting point for a more in-depth discussion of a research strategy, gaps in physics and engineering need to be investigated. Open aspects are the confinement of fast fusion-born particles and the behaviour of a burning plasma with considerable production of fusion power in a 3D magnetic topology. Apart from direct losses of fast particles, a sufficiently large pressure of fast particles may excite and interact with Alfvénic instabilities causing additional transport. As the confinement of the fast alpha particles is a key requirement for the self-sustained burn of a fusion power plant, a burning-plasma stellarator experiment allows clarifying these aspects for 3D magnetic configurations. From a systemic point of view, such a device also allows to elucidate on other uncertainties, e.g. the role of turbulent transport. It has recently been found that in W7-X the ITG mode is mostly located in a thin band on the outboard side of the torus, i.e. the properties of the magnetic configuration seem to play an important role, which can be incorporated in future optimization procedures. Investigation in a stellarator burning-plasma experiment allows, therefore, to obtain a clear systemic physics and engineering basis.
Several different strategies could be followed for such a device ranging from a fast-track, cost-efficient device without blanket to a nearly DEMO-like machine requiring a full set of reactor systems. For each concept, a design analysis has been carried out using a systems code approach to define possible scenarios. The individual design points are compared in this common framework showing a factor of two differences in costs between the smallest reasonable (R=14m) and a DEMO-like (R=18m) device requiring in addition considerable technological development. It is expected that experience from the tokamak development (e.g. ITER) can be used to reduce the total effort.
To substantiate these studies, further criteria are discussed to make a sensible choice on which design shall be followed. Especially the difference in technological readiness must be taken into account and it should be assessed to what degree synergy effects with the development towards a tokamak-DEMO can be expected.
Co-authors
A. Dinklage
(Max Planck Institute for Plasma Physics, Wendelsteinstraße 1, 17489 Greifswald, Germany)
C. D. Beidler
(Max Planck Institute for Plasma Physics, Wendelsteinstraße 1, 17489 Greifswald, Germany)
F. Warmer
(Max Planck Institute for Plasma Physics, Wendelsteinstraße 1, 17489 Greifswald, Germany)
R. C. Wolf
(Max Planck Institute for Plasma Physics, Wendelsteinstraße 1, 17489 Greifswald, Germany)
the W7-X Team
(Max Planck Institute for Plasma Physics, Wendelsteinstraße 1, 17489 Greifswald, Germany)
