Toward Improved Stellarators Future Directions for U.S. Research

Authors: G. H. Neilson

Abstract: Steady state high-performance, transients, and efficient current-drive are major challenges for magnetic fusion energy (MFE). Stellarators offer promising solutions, and indeed there is a world program, including two large experiments developing stellarators, Japan's Large Helical Device (LHD) and Germany's Wendelstein 7-X (W7 X), both designed around 1990. Advances in stellarator physics and engineering in the years since these experiments were designed have the potential to substantially improve future stellarator-based fusion systems. These advances, which define the priorities for stellarator research in the U.S., are in the following areas: quasi-symmetric configurations, turbulent transport optimization, divertors and plasma-material interactions, impurity control, energetic particles, and engineering optimization. Currently, U.S. stellarator experimental research is carried out through a major collaboration with Germany's Wendelstein 7-X program and on smaller domestic experiments. A theory and design activity is proposed as a next step toward developing and evaluating new designs that can become the basis for new experimental facilities that would then be constructed. It is argued that, with timely action, new U.S. experiments could begin to come on line in the 2020s and could impact the direction of fusion development in the ITER era and decisions on next steps beyond ITER.

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