Topology-mediated approach to the design of quasisymmetric stellarators

Rodriguez, Eduardo D.; Sengupta, Wrick; Bhattacharjee, Amitava

doi:10.48550/arxiv.2204.10234

Cited by 3 publications

(13 citation statements)

References 30 publications

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“…The QH solutions for any given n fp also occupy continuous bands with a wide range of axis lengths. Analogous features have been observed recently by Rodriguez et al (2022b).…”

Section: Parameter Scanssupporting

confidence: 88%

“…The QH solutions have ι > 0.9. As recently observed by Rodriguez et al (2022b), QH and QA solutions exist in continuous bands along which the axis length varies. Along the QA bands, ι varies significantly, whereas ι varies more weakly along the QH bands.…”

Section: Discussionsupporting

confidence: 65%

“…The plasma shape is shown in figure 11 for a = 0.13, corresponding to A = 5.8. The axis shape of this configuration resembles the one in figure 2 of Rodriguez et al (2022b). Given the boundary computed by the near-axis equations, the field strength inside is computed with DESC and displayed in figure 12, showing excellent QH symmetry.…”

Section: Quasi-helical Symmetry With Four Field Periodsmentioning

confidence: 80%

“…One purpose of the present article is to give a detailed presentation. A different approach for choosing parameters of the near-axis model and mapping the space of solutions was proposed in Rodriguez, Sengupta & Bhattacharjee (2022b). Optimization of a near-axis quasi-isodynamic (QI) stellarator was presented recently in Jorge et al (2022).…”

Section: Introductionmentioning

confidence: 99%

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Mapping the space of quasisymmetric stellarators using optimized near-axis expansion

Landreman

2022

J. Plasma Phys.

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A method is demonstrated to rapidly calculate the shapes and properties of quasi-axisymmetric and quasi-helically symmetric stellarators. In this approach, optimization is applied to the equations of magnetohydrodynamic equilibrium and quasisymmetry, expanded in the small distance from the magnetic axis, as formulated by Garren & Boozer [Phys. Fluids B, vol. 3, 1991, p. 2805]. Due to the reduction of the equations by the expansion, the computational cost is significantly reduced, to times of the order of 1 cpu second, enabling wide and high-resolution scans over parameter space. In contrast to traditional stellarator optimization, here, the cost function serves to maximize the volume in which the expansion is accurate. A key term in the cost function is $\| \boldsymbol {\nabla }\boldsymbol B \|$ , the norm of the magnetic field gradient, to maximize scale lengths in the field. Using this method, a database of $5\times 10^5$ optimized configurations is calculated and presented. Quasisymmetric configurations are observed to exist in continuous bands, varying in the ratio of the magnetic axis length to average major radius. Several qualitatively new types of configuration are found, including quasi-helically symmetric fields in which the number of field periods is two or more than six.

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“…The QH solutions for any given n fp also occupy continuous bands with a wide range of axis lengths. Analogous features have been observed recently by Rodriguez et al (2022b).…”

Section: Parameter Scanssupporting

confidence: 88%

Section: Discussionsupporting

confidence: 65%

Section: Quasi-helical Symmetry With Four Field Periodsmentioning

confidence: 80%

Section: Introductionmentioning

confidence: 99%

See 2 more Smart Citations

Mapping the space of quasisymmetric stellarators using optimized near-axis expansion

Landreman

2022

J. Plasma Phys.

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“…The first is the onaxis ι of the original NCSX design [4], while the second and third are substantially larger noble irrationals. It is known that QA becomes progressively more difficult to achieve as ι grows [23,24,25], so choosing two large ι target values serves as a challenging test for our methods, especially since we only consider the vacuum field. We initialize the optimization using the modular coil design parameters of NCSX [4,26], but add two planar coils per half field period.…”

Section: Optimization For Flexible Qa Configurationmentioning

confidence: 99%

Stellarator coil optimization supporting multiple magnetic configurations

Lee,

Paul,

Stadler

et al. 2022

Preprint

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We present a technique that can be used to design stellarators with a high degree of experimental flexibility. For our purposes, flexibility is defined by the range of values the rotational transform can take on the magnetic axis of the vacuum field while maintaining satisfactory quasisymmetry. We show that accounting for configuration flexibility during the modular coil design improves flexibility beyond that attained by previous methods. Careful placement of planar control coils and the incorporation of an integrability objective enhance the quasisymmetry and nested flux surface volume of each configuration. We show that it is possible to achieve flexibility, quasisymmetry, and nested flux surface volume to reasonable degrees with a relatively simple coil set through an NCSXlike example. This preliminary coil design is optimized to achieve three rotational transform targets and nested flux surface volumes in each magnetic configuration larger than the NCSX design plasma volume. Our work suggests that there is a tradeoff between flexibility, quasisymmetry, and volume of nested flux surfaces.

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Magnetohydrodynamic stability and the effects of shaping: a near-axis view for tokamaks and quasisymmetric stellarators

Rodríguez

2023

J. Plasma Phys.

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How much does the cross-section of a toroidal magnetic field configuration tell us about its magnetohydrodynamic (MHD) stability? It is generally believed that positive triangularity (typically leading to bean-shaped cross-sections with their indentation on the inboard side in stellarators) contributes positively to MHD stability. In this paper, we explore the basis of this statement within a near-axis description for axisymmetric and quasisymmetric magnetic configurations. In agreement with the existing literature, we show that positive triangularity stabilises vertically elongated tokamaks. In quasisymmetric stellarators, the toroidal asymmetry of flux surfaces modifies this relation. The behaviour of stellarator-symmetric, quasisymmetric stellarators can still be described in terms of the shape of one of their up–down symmetric cross-sections. However, we show that for a sample of quasisymmetric configurations, the positive-bean-shaped cross-sections do not contribute positively to stability. Unlike in the axisymmetric case, we also learn that finite $\beta$ can improve stability even without magnetic shear.

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Topology-mediated approach to the design of quasisymmetric stellarators

Cited by 3 publications

References 30 publications

Mapping the space of quasisymmetric stellarators using optimized near-axis expansion

Mapping the space of quasisymmetric stellarators using optimized near-axis expansion

Stellarator coil optimization supporting multiple magnetic configurations

Magnetohydrodynamic stability and the effects of shaping: a near-axis view for tokamaks and quasisymmetric stellarators

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