Helical coil stellarators with good outboard side access

A helical-coil stellarator configuration is presented using the HSX plasma surface. The bulk of the vacuum magnetic field should be produced by two helical coils which pass near the plasma on the inboard side at the helical twist of the plasma surface and pass far away on the outboard side of the plasma. This configuration would offer numerous benefits: (1) the large outboard side coil-plasma gap allows (a) easy access to the plasma chamber, (b) room to install plasma diagnostics and breeding blankets, and (c) easy field modification using trim coils, (2) the simplicity of coil production for an optimized stellarator plasma, and (3) toroidal ripples can be reduced since the helical coil is continuous. To achieve this coil design we will use adjoint REGCOIL¹ using a combination of guesses for the winding surface guided by low aspect ratio analytic theory and a regularization function which encourages solutions with concentrated current densities located far from the plasma surface on the outboard side.