The pseudo-symmetric optimization of the National Compact Stellarator Experiment

A new experiment, the National Compact Stellarator Experiment (NCSX) [Monti cello "Physics Consideration for the Design of NCSX," Proceedings of 25th E PS Conference on Controlled Fusion and Plasma Physics, Prague, 1998 (Europe an Physical Society, Petit-Lancy), paper 1.187], hopes to overcome the dele terious ripple transport usually associated with stellarators by creating a quasi-axisymmetric configuration. A quasi-axisymmetric configuration is on e in which the Fourier spectrum of the magnetic field strength in so-called Boozer coordinates is dominated by the toroidal angle averaged (n=0) compo nents. In this article the concept of pseudosymmetry is used to improve rip ple transport in a four-period variant of NCSX. By definition, pseudosymmet ric magnetic configurations have no locally trapped particles. To obtain a pseudosymmetric configuration, different target functions are considered. I t is found that a target function equal to the area of ripple of the magnet ic field magnitude along the field line is very effective in reducing the n eoclassical transport coefficient. (C) 1999 American Institute of Physics. [S1070-664X(99)01108-8].