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Spline representations for more efficient stellarator coil design

Author: Joshua A. Breslau
Requested Type: Consider for Invited
Submitted: 2012-12-06 09:44:53

Co-authors: N. Pomphrey, J.X. Zheng

Contact Info:
Princeton Plasma Physics Laboratory
P.O. Box 451
Princeton, NJ   08542-0
USA

Abstract Text:
From an engineering perspective, the chief drawback of modern stellarator designs is the high complexity of their magnetic coils: the irregular three-dimensional shapes are challenging to wind and assemble to the required tolerances, and the assembled coil sets encircle the device in a manner that impedes access for ports or routine maintenance. The substitution of modular coil systems with long straight outer legs supplemented by saddle coils could, if compatible with required plasma properties, address both these problems. The commonly used [1] Fourier representation of coil shapes within a winding surface does not easily lend itself to the design of straight coil sections, nor to refinement of a local coil feature without re-optimizing the entire length of the coil. We introduce a new design tool, COILOPT++, making use of a cubic B-spline coil representation that offers several advantages over the Fourier model. In addition to allowing the straightforward joining of curved and straight sections with second-order continuity in curvature, the spline approach allows for faster, more efficient, and more interactive customization, and makes closer contact with the engineering tools needed to specify the final finite-thickness shapes of the conductors to be wound. The new tool is demonstrated to produce modular coil shapes as efficient as those calculated by the original Fourier-based COILOPT in the limit of no straight sections, while adding the flexibility needed to produce improved designs containing these sections.

[1] D. J. Strickler, L. A. Berry, and S. P. Hirshman, Fusion Sci. and Technol. 41, 107 (2002).

Characterization: 1.4

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