The pseudo-symmetric optimization of the National Compact Stellarator Experiment

A new experiment, the National Compact Stellarator Experiment (NCSX) [Monticello et al. “Physics Consideration for the Design of NCSX,” Proceedings of 25th EPS Conference on Controlled Fusion and Plasma Physics, Prague, 1998 (European Physical Society, Petit-Lancy), paper 1.187], hopes to overcome the deleterious ripple transport usually associated with stellarators by creating a quasi-axisymmetric configuration. A quasi-axisymmetric configuration is one in which the Fourier spectrum of the magnetic field strength in so-called Boozer coordinates is dominated by the toroidal angle averaged [formula omitted] components. In this article the concept of pseudosymmetry is used to improve ripple transport in a four-period variant of NCSX. By definition, pseudosymmetric magnetic configurations have no locally trapped particles. To obtain a pseudosymmetric configuration, different target functions are considered. It is found that a target function equal to the area of ripple of the magnetic field magnitude along the field line is very effective in reducing the neoclassical transport coefficient.