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(FTP2/08) Compact Stellarator Coils

N. Pomphrey¹⁾, L. A. Berry²⁾, A. H. Boozer³⁾, A. Brooks¹⁾, R. Hatcher¹⁾, S. Hirshman²⁾, L. P. Ku¹⁾, W. Miner⁴⁾, H. Mynick¹⁾, W. Reiersen¹⁾, D. Strickler²⁾, P. Valanju^4)
 
1) Princeton Plasma Physics Laboratory, Princeton, NJ 08543, USA
²⁾ Oak Ridge National Laboratory, Oak Ridge, TN 37831-8070, USA
³⁾ Columbia University, New York, NY 10027, USA
⁴⁾ University of Texas at Austin, Austin, TX 78712-1081, USA

Abstract.  Experimental devices to study the physics of high-beta ( $\beta$ $\gtrsim$ 4%), low aspect ratio ( A $\lesssim$ 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 the stellarator boundary must be targeted if a coil set is to provide fields to control the essential physics of the plasma; the use of Genetic Algorithms 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

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