Solving the problem of overdetermination of quasisymmetric equilibrium solutions by near-axis expansions. II. Circular axis stellarator solutions

Abstract

We apply the near-axis expansion method for quasisymmetric magnetic fields with anisotropic pressure (developed in Paper I) [E. Rodriguez and A. Bhattacharjee, Phys. Plasmas 28, 012508 (2020)] to construct numerical solutions to circular axis stellarators. The solutions are found to second order in the distance from the axis, not possible in the standard Garren–Boozer construction [D. A. Garren and A. H. Boozer, Phys. Fluids B 3, 2822 (1991)], which assumes magnetostatic equilibria with isotropic pressure. In the limit of zero anisotropy, it is shown that a subset of coefficients can be chosen to avoid the overdetermination problem.