Optimizing Stellarators for Turbulent Transport

N.Pomphrey, and P. Xanthopoulos H.E. Mynick

doi:10.2172/981714

Cited by 11 publications

(27 citation statements)

References 7 publications

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“…In this work, the two quasi-symmetric configurations under consideration are quasi-helical symmetry, specifically the HSX geometry, where the mode dominates, and quasi-axisymmetry, specifically the NCSX geometry (Mynick et al. 2010), where the mode dominates.…”

Section: Quasi-symmetric Stellaratorsmentioning

confidence: 99%

“…2005; Mynick et al. 2010; Mynick, Pomphrey & Xanthopoulos 2011; Hegna et al. 2018) owing in part to the lower computational costs.…”

Section: Adiabatic-electron Simulationsmentioning

confidence: 99%

“…It should be noted that results presented by Mynick et al. (2010) have shown the successful optimization of ITG turbulent transport over a range of quasi-axisymmetric stellarator configurations by using a quasilinear proxy for the nonlinear heat flux. It should also be noted that recent results have successfully reproduced ITG turbulent transport in helical plasmas using quasilinear estimates that include the effects of zonal flows (Nunami, Watanabe & Sugama 2013; Toda et al.…”

Section: Introductionmentioning

confidence: 99%

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A comparison of turbulent transport in a quasi-helical and a quasi-axisymmetric stellarator

et al. 2019

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Ion-temperature-gradient-driven (ITG) turbulence is compared for two quasi-symmetric (QS) stellarator configurations to determine the relationship between linear growth rates and nonlinear heat fluxes. We focus on the quasi-helically symmetric (QHS) stellarator HSX and the quasi-axisymmetric (QAS) stellarator NCSX. In normalized units, HSX exhibits higher growth rates than NCSX, while heat fluxes in gyro-Bohm units are lower in HSX. These results hold for simulations made with both adiabatic and kinetic electrons. The results show that HSX has a larger number of subdominant modes than NCSX and that eigenmodes are more spatially extended in HSX. We conclude that the consideration of nonlinear physics is necessary to accurately assess the heat flux due to ITG turbulence when comparing QS stellarator equilibria.

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Section: Quasi-symmetric Stellaratorsmentioning

confidence: 99%

“…2005; Mynick et al. 2010; Mynick, Pomphrey & Xanthopoulos 2011; Hegna et al. 2018) owing in part to the lower computational costs.…”

Section: Adiabatic-electron Simulationsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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A comparison of turbulent transport in a quasi-helical and a quasi-axisymmetric stellarator

et al. 2019

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“…2019 b ). Advances in theoretical understanding have produced mechanisms for optimization in the areas of turbulent transport (Mynick, Pomphrey & Xanthopoulos 2010; Xanthopoulos et al. 2014; Hegna, Terry & Faber 2018), energetic particle transport (Bader et al.…”

Section: Introductionmentioning

confidence: 99%

“…These advances come in several forms including the identification of new quasi-axisymmetric configurations (Henneberg et al 2019b). Advances in theoretical understanding have produced mechanisms for optimization in the areas of turbulent transport (Mynick, Pomphrey & Xanthopoulos 2010;Xanthopoulos et al 2014;, energetic particle transport (Bader et al 2019;Henneberg, Drevlak & Helander 2019a) and non-resonant divertors (Bader et al 2018). Also, construction of optimized equilibria from first principles has been demonstrated for quasi-symmetric stellarators (Landreman & Sengupta 2018;Landreman, Sengupta & Plunk 2019) and quasi-omnigenous stellarators .…”

Section: Introductionmentioning

confidence: 99%

Advancing the physics basis for quasi-helically symmetric stellarators

et al. 2020

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A new optimized quasi-helically symmetric configuration is described that has the desirable properties of improved energetic particle confinement, reduced turbulent transport by three-dimensional shaping and non-resonant divertor capabilities. The configuration presented in this paper is explicitly optimized for quasi-helical symmetry, energetic particle confinement, neoclassical confinement and stability near the axis. Post optimization, the configuration was evaluated for its performance with regard to energetic particle transport, ideal magnetohydrodynamic stability at various values of plasma pressure and ion temperature gradient instability induced turbulent transport. The effects of discrete coils on various confinement figures of merit, including energetic particle confinement, are determined by generating single-filament coils for the configuration. Preliminary divertor analysis shows that coils can be created that do not interfere with expansion of the vessel volume near the regions of outgoing heat flux, thus demonstrating the possibility of operating a non-resonant divertor.

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Near-axis expansion of stellarator equilibrium at arbitrary order in the distance to the axis

2020

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A direct construction of equilibrium magnetic fields with toroidal topology at arbitrary order in the distance from the magnetic axis is carried out, yielding an analytical framework able to explore the landscape of possible magnetic flux surfaces in the vicinity of the axis. This framework can provide meaningful analytical insight on the character of high-aspect-ratio stellarator shapes, such as the dependence of the rotational transform and the plasma beta-limit on geometrical properties of the resulting flux surfaces. The approach developed here is based on an asymptotic expansion on the inverse aspectratio of the ideal MHD equation. The analysis is simplified by using an orthogonal coordinate system relative to the Frenet-Serret frame at the magnetic axis. The magnetic field vector, the toroidal magnetic flux, the current density, the field line label and the rotational transform are derived at arbitrary order in the expansion parameter. Moreover, a comparison with a near-axis expansion formalism employing an inverse coordinate method based on Boozer coordinates (the so-called Garren-Boozer construction) is made, where both methods are shown to agree at lowest order. Finally, as a practical example, a numerical solution using a W7-X equilibrium is presented, and a comparison between the lowest order solution and the W7-X magnetic field is performed. †

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Optimizing Stellarators for Turbulent Transport

Cited by 11 publications

References 7 publications

A comparison of turbulent transport in a quasi-helical and a quasi-axisymmetric stellarator

A comparison of turbulent transport in a quasi-helical and a quasi-axisymmetric stellarator

Advancing the physics basis for quasi-helically symmetric stellarators

Near-axis expansion of stellarator equilibrium at arbitrary order in the distance to the axis

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