Compact Stellarator Coils
Authors: N. Pomphrey, L. Berry, A. Boozer, A. Brooks, R.E. Hatcher, S.P. Hirshman, L.-P. Ku, W.H. Miner, H.E. Mynick, W. Reiersen, D.J. Strickler, and P.M. Valanju
Date of PPPL Report: November 2000
Presented at: the 18th International Atomic Energy Agency's (IAEA) Fusion Energy Conference 2000 (FEC-2000) held in Sorrento, Italy, October 4-10, 2000. An unedited proceedings will be published by IAEA in electronic format (CD-ROM).
Edited, refereed version published in: Nucl. Fusion 41 (March 2001) 339-347. (Title changed to: Innovations in Compact Stellarator Coil Design.)
Experimental devices to study the physics of high-beta (b is greather than or approximately equal to 4%), low aspect ratio (A is less than or approximately equal to 4.5) stellarator plasmas require coils that will produce plasmas satisfying a set of physics goals, provide experimental flexibility, and be practical to construct. In the course of designing a flexible coil set for the National Compact Stellarator Experiment, we have made several innovations that may be useful in future stellarator design efforts. These include: the use of Singular Value Decomposition methods for obtaining families of smooth current potentials on distant coil winding surfaces from which low current density solutions may be identified; the use of a Control Matrix Method for identifying which few of the many detailed elements of a stellarator boundary must be targeted if a coil set is to provide fields to control the essential physics of the plasma; the use of a Genetic Algorithm for choosing an optimal set of discrete coils from a continuum of potential contours; the evaluation of alternate coil topologies for balancing the tradeoff between physics objective and engineering constraints; the development of a new coil optimization code for designing modular coils, and the identification of a "natural" basis for describing current sheet distributions.