Innovations in compact stellarator coil design

Experimental devices for the study of the physics of high beta (beta greate r than or similar to 4%); low aspect ratio (A less than or similar to 4.5) stellarator plasmas require coils that will produce plasmas satisfying a se t of physics goals, provide experimental flexibility and be practical to co nstruct. In the course of designing a flexible coil set for the National Co mpact Stellarator Experiment, several innovations have been made that may b e useful in future stellarator design efforts. These include: the use of si ngular 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 identi fying which few of the many detailed elements of a stellarator boundary mus t be targeted if a coil set is to provide fields to control the essential p hysics of the plasma; the use of a genetic algorithm for choosing an optima l set of discrete coils from a continuum of potential contours; the evaluat ion of alternate coil topologies for balancing the trade-off between physic s objectives and engineering constraints; the development of a new coil opt imization code for designing modular coils and the identification of a 'nat ural' basis for describing current sheet distributions.