Existence of an optimized stellarator with simple coils

We propose a new method to compute magnetic surfaces that are parametrized in Boozer coordinates for vacuum magnetic fields. We also propose a measure for quasisymmetry on the computed surfaces and use it to design coils that generate a magnetic field that is quasisymmetric on those surfaces. The rotational transform of the field and complexity measures for the coils are also controlled in the design problem. Using an adjoint approach, we are able to obtain analytic derivatives for this optimization problem, yielding an efficient gradient-based algorithm. Starting from an initial coil set that presents nested magnetic surfaces for a large fraction of the volume, our method converges rapidly to coil systems generating fields with excellent quasisymmetry and low particle losses. In particular for low complexity coils, we are able to significantly improve the performance compared with coils obtained from the standard two-stage approach, e.g. reduce losses of fusion-produced alpha particles born at half-radius from $17.7\,\%$ to $6.6\,\%$ . We also demonstrate 16-coil configurations with alpha loss ${<}1\,\%$ and neoclassical transport magnitude $\epsilon _{\text {eff}}^{3/2}$ less than approximately $5\times 10^{-9}$ .

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“…2022 a ; Yu et al. 2022). It has the potential to yield designs with coil systems that are easier to manufacture and position.…”

Section: Introductionmentioning

confidence: 99%

Direct computation of magnetic surfaces in Boozer coordinates and coil optimization for quasisymmetry

et al. 2022

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“…for quasi-axisymmetry, (1, −1), for quasi-helical symmetry, (10) which are the two allowed flavors of quasisymmetry close to the magnetic axis [29]. We use this particular form of quasisymmetry, equation ( 9), primarily due to its accessibility within the SIMSOPT framework and its demonstrated smoothness and convergence properties.…”

Section: Optimization Methodsmentioning

confidence: 99%

“…We first apply this method to find a set of four simplified coils, two circular coils at the top and bottom of the device, and two interlinking coils. Similar configurations include Columbia Non-neutral Torus (CNT) device [41], a stellarator experiment at Columbia University with four circular coils which are used here as the starting point for the optimization, and the Compact Stellarator with Simple Coils (CSSC) [10]. First, we perform an optimization with the top and bottom coils fixed, while the two symmetric interlinking coils are allowed to vary.…”

Section: Four-coil Stellaratormentioning

confidence: 99%

“…Previous combined optimization methods have either relied directly or indirectly on free boundary equilibrium calculations [3][4][5][6][7], which often demand many iterations between an equilibrium solution, or these can only be used with vacuum configurations [8][9][10][11][12]. In [13] several combined optimization approaches were discussed, including the possibility of using fixed boundary equilibria and the corresponding penalty functionals.…”

Section: Introductionmentioning

confidence: 99%

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Single-stage stellarator optimization: combining coils with fixed boundary equilibria

Jorge

Goodman

Landreman

et al. 2023

Plasma Phys. Control. Fusion

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We introduce a novel approach for the simultaneous optimization of plasma and coil engineering objectives in a fixed-boundary equilibrium that is computationally efficient and applicable to a broad range of vacuum and finite plasma pressure scenarios. Our approach treats plasma boundary and coil shapes as independently optimized variables, penalizing the mismatch between the two using a quadratic flux term in the objective function. Four use cases are presented to demonstrate the effectiveness of the approach, including simple and complex stellarator geometries. As it is shown here, this method outperforms previous 2-stage approaches, achieving smaller plasma objective function values when coils are taken into account.

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FP3D: A code for calculating 3D magnetic field and particle motion

Jiang,

Feng,

et al. 2024

Physics of Plasmas

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An efficient numerical code FP3D has been developed to calculate particle orbits and evaluate particle confinement in 3D magnetic fields including stellarators and tokamaks with 3D fields. The magnetic field is either calculated from coils directly or obtained from equilibrium codes. FP3D has been verified with the 3D equilibrium code Variational Moments Equilibrium Code [Hirshman and Whitson, Phys. Fluids 26, 3553–3568 (1983)] for magnetic field calculation and with the drift-kinetic code Stellarator Fokker–Planck Iterative Neoclassical Conservative Solver [Landreman et al., Phys. Plasmas 21(4), 042503 (2014)] for neoclassical transport. The code has been applied successfully to the National Compact Stellarator Experiment stellarator [Nelson et al., Fusion Eng. Des. 66, 169–174 (2003)] for the calculation of neoclassical transport coefficient with the 3D magnetic field obtained directly from coils. FP3D is also used to calculate ripple losses in the tokamak Experimental Advanced Superconducting Tokamak [Y. Wan, Plasma Sci. Technol. 8(3) (2006)].

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Existence of an optimized stellarator with simple coils

Cited by 4 publications

References 26 publications

Direct computation of magnetic surfaces in Boozer coordinates and coil optimization for quasisymmetry

Direct computation of magnetic surfaces in Boozer coordinates and coil optimization for quasisymmetry

Single-stage stellarator optimization: combining coils with fixed boundary equilibria

FP3D: A code for calculating 3D magnetic field and particle motion

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