Stellarator coil design using cubic splines for improved access on the outboard side

TL;DR

This paper introduces a spline-based coil design method for stellarators using the FOCUS code, enabling more accessible and maintainable coils by incorporating new engineering constraints and flexible representations.

Contribution

It implements spline representation and a new engineering constraint in FOCUS, enhancing coil design flexibility and accessibility for stellarators.

Findings

Spline representation improves coil shape flexibility.

New constraint produces straighter outer coil sections.

Designs demonstrated on HSX, NCSX, and a prototype stellarator.

Abstract

In recent years many efforts have been undertaken to simplify coil designs for stellarators due to the difficulties in fabricating non-planar coils. The FOCUS code removes the need for a winding surface and represents the coils as arbitrary curves in 3D. In the following work, the implementation of a spline representation for the coils in FOCUS is described, along with the implementation of a new engineering constraint to design coils with a straighter outer section. The new capabilities of the code are shown as an example on HSX, NCSX, and a prototype quasi-axisymmetric reactor-sized stellarator. The flexibility granted by splines along with the new constraint will allow for stellarator coil designs with improved accessibility and simplified maintenance