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Motivations and Opportunities for a Renewed U.S. Domestic Stellarator Program

Author: G. H. Neilson
Requested Type: Consider for Invited
Submitted: 2012-12-07 09:23:32

Co-authors: D. A. Gates, M. C. Zarnstorff, J. H. Harris, G. A. Wurden

Contact Info:
Princeton Plasma Physics Laboratory
P.O. Box 451, MS-38
Princeton, NJ   08453
United States of Ame

Abstract Text:
The benefits of stellarators have been extensively documented and reviewed, and are widely understood and accepted. The U.S. has long been a leader in the field, with contributions that include the development of quasi-symmetric (QS) stellarators, an innovation that can manifest the traditional stellarator advantages of steady-state without current drive or disruptions in a low-ripple, low flow-damping, reduced aspect-ratio configuration. The concept is sufficiently different from other toroidal concepts as to offer high potential for breakthroughs and new science, yet its design and performance projections have their basis in well-developed physics of stellarators and tokamaks.
With the world fusion community now laying out the steps beyond ITER to electricity-generating fusion systems, there are new motivations to accelerate the development of QS stellarators. Recent studies [1] comparing options for steady-state, energy-breakeven (Qeng = 1) fusion nuclear facility demonstrate important advantages of a QS stellarator over an advanced tokamak (AT) or spherical tokamak (ST), stemming from the elimination of current drive, disruptions, and feedback control of unstable MHD modes, advantages that are well established for stellarators generally. Advances in stellarator optimization have created opportunities to improve QS stellarator designs in terms of both their physics [2] and their coil engineering properties [3]. Development of the QS stellarator can build on results from burning plasma experiments in ITER as well as from long-pulse, diverted 3D plasma experiments in LHD and Wendelstein 7-X. The basic principles of QS design have been validated by the HSX experiment, and larger experiments are needed to perform integrated tests and develop the concept.
Options for a leadership-class U.S. stellarator program include at least two: 1) completion of the NCSX device and its mission, and 2) a new stellarator with a broader mission and a more advanced design than NCSX. The NCSX is a technically well understood option that could move forward rapidly in response to a near-term opportunity. A new stellarator could incorporate design advances beyond NCSX, resulting in simpler coils and better plasma performance. A QS stellarator of the LHD and W7-X class, operating in the 2020s, would have large international impact and would significantly improve the technical basis for MFE DEMO design decisions.
[1] G. H. Neilson et al., "Mission and Readiness Assessment for Fusion Nuclear Facilities," TOFE-2012 paper, to be published in Fusion Science and Technology.
[2] H. E. Mynick, "Progress in turbulent optimization of toroidal configurations," this conference.
[3] J. A. Breslau, "Spline representations for more efficient stellarator coil design," this conference.

Research supported by the U.S. DOE under Contract No. DE-AC02-09CH11466 with Princeton University

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