Coil optimization methods for a planar coil stellarator
Thomas Krüger, Mike F. Martin, D. Gates, the Thea Energy Team
Abstract
Abstract The planar coil stellarator design is a novel approach to producing the confining magnetic field of a stellarator plasma. The work presented here details the optimization of the two types of planar coils that are used in the planar coil design: the plasma encircling coils, and the shaping coils. The plasma encircling coils provide the mean magnetic field and linking current, similar to the toroidal field (TF) coils in a tokamak. The plasma encircling coils can be rotationally symmetric TF-like coils and produce a <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mrow> <mml:mi>B</mml:mi> <mml:mo>∝</mml:mo> <mml:mn>1</mml:mn> <mml:mrow> <mml:mo>/</mml:mo> </mml:mrow> <mml:mi>R</mml:mi> </mml:mrow> </mml:math> field, but optimizing their placement, tilt, and shaping can substantially reduce the magnetic field error. In addition, an array of dipole-like shaping coils, that lie on a surface between the plasma boundary and the encircling coils, correct for the residual magnetic field error following encircling coil optimization. As a proof-of-concept, it is shown that by optimizing both types of coils, subject to realistic engineering constraints, reasonable magnetic field errors of ∼1% have been achieved. Comparison to a traditional modular coil set reveals that similarly low magnetic field errors can be attained with the planar coil stellarator.