The theoretical and experimental development of stellarators has removed some of the specific deficiencies of this configuration, viz., the limitations in β, the high neoclassical transport, and the low collisionless confinement of α particles. These optimized stellarators can best be realized with a modular coil system. The W7-AS experiment [Plasma Phys. Controlled Fusion 31, 1579 (1989)] has successfully demonstrated two aspects of advanced stellarators, the improved equilibrium and the modular coil concept. Stellarator optimization will much more viably be demonstrated by W7-X [Plasma Physics and Controlled Fusion Research, Proceedings of the 12th International Conference, Nice, 1988 (IAEA, Vienna, 1989), Vol. 2, p. 369], the successor experiment presently under design. Optimized stellarators seem to offer an independent reactor option. In addition, they supplement, in a unique form, the toroidal confinement fusion program, e.g., energy transport is anomalous in stellarators too, but possibly more easily understandable in the frame of existing theoretical concepts than in tokamaks.
In many stellarators-envisagcd as fusion deviccs--any a-particle which cver gets reflected (all = 0) is collisionlcssly lost in a time which is orders ofmagnitude smaller than the typical slowing-down time of =IO-' s. Two classes of stellarators to which this general picture docs not apply arc dcscribcd: quasi-helically symmetric stellarators and a class ofstellarators with vanishing bootstrap current in which the collisionless r-particle confinement sufficiently improves at finile 8. The influence of the modular ripple in optimized coil systems realizing these configurations, the angular distribution of the kast e-particle losses, and the application of the rcsults to a-particle confinemcnt Simulation experiments in next-generation stellaialors are also discussed
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