@article{306,
  keywords = {Stellarators, plasma confinement, Magnetohydrodynamics, optimization},
  author = {A. Baillod and J. Loizu and J. Graves and M. Landreman},
  title = {Stellarator optimization for nested magnetic surfaces at finite β and toroidal current},
  abstract = {<p>Good magnetic surfaces, as opposed to magnetic islands and chaotic field lines, are generally desirable for stellarators. In previous work, Landreman\&nbsp;<em>et al.</em>\&nbsp;[Phys. of Plasmas\&nbsp;<strong>28</strong>, 092505 (2021)] showed that equilibria computed by the Stepped-Pressure Equilibrium Code (SPEC) [Hudson\&nbsp;<em>et al.</em>, Phys. Plasmas\&nbsp;<strong>19</strong>, 112502 (2012)] could be optimized for good magnetic surfaces in vacuum. In this paper, we build upon their work to show the first finite-<em>β</em>, fixed-, and free-boundary optimization of SPEC equilibria for good magnetic surfaces. The objective function is constructed with the Greene{\textquoteright}s residue of selected rational surfaces, and the optimization is driven by the SIMSOPT framework [Landreman\&nbsp;<em>et al.</em>, J. Open Source Software\&nbsp;<strong>6</strong>, 3525 (2021)]. We show that the size of magnetic islands and the consequent regions occupied by chaotic field lines can be minimized in a classical stellarator geometry (rotating ellipse) by optimizing either the injected toroidal current profile, the shape of a perfectly conducting wall surrounding the plasma (fixed-boundary case), or the vacuum field produced by the coils (free-boundary case). This work shows that SPEC can be used as an equilibrium code both in a two-step or single-step stellarator optimization loop.</p>
},
  year = {2022},
  journal = {Physics of Plasmas},
  volume = {29},
  number = {4},
  pages = {042505},
  month = {04/2022},
  url = {https://doi.org/10.1063/5.0080809},
  doi = {10.1063/5.0080809},
}