A model for the fast evaluation of prompt losses of energetic ions in stellarators

Velasco, J. L.; Calvo, I.; Mulas, S.; Sánchez, E.; Parra, Felix; Cappa, Á.; Team, the W7-X

doi:10.1088/1741-4326/ac2994

Cited by 14 publications

(34 citation statements)

References 33 publications

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“…1992; Velasco et al. 2021). Physically, changes in poloidal precession are also the cause of the aforementioned catastrophic , but it is instructive to think of these two phenomena separately in this case.…”

Section: Discussionmentioning

confidence: 99%

Constructing precisely quasi-isodynamic magnetic fields

Goodman,

Camacho Mata,

Henneberg

et al. 2023

J. Plasma Phys.

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We present a novel method for numerically finding quasi-isodynamic stellarator magnetic fields with excellent fast-particle confinement and extremely small neoclassical transport. The method works particularly well in configurations with only one field period. We examine the properties of these newfound quasi-isodynamic configurations, including their transport coefficients, particle confinement and available energy for trapped-electron-instability-driven turbulence, as well as the degree to which they change when a finite pressure profile is added. We finally discuss the differences between the magnetic axes of the optimized solutions and their respective initial conditions, and conclude with the prospects for future quasi-isodynamic optimization.

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Section: Discussionmentioning

confidence: 99%

Constructing precisely quasi-isodynamic magnetic fields

Goodman,

Camacho Mata,

Henneberg

et al. 2023

J. Plasma Phys.

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“…2005; Velasco et al. 2021; LeViness et al. 2023), classifiers presented here are based on real orbits retaining their actual radial widths which can be compatible with plasma radius (see Albert et al.…”

Section: Discussionmentioning

confidence: 99%

“…Note, that in the bounce-averaged approximation (Velasco et al. 2021), only transient orbits appear as chaotic. In the full guiding-centre model, where the bounce phase is retained, transient orbits cannot only be chaotic (as for the ones studied, e.g.…”

Section: Methodsmentioning

confidence: 99%

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Alpha particle confinement metrics based on orbit classification in stellarators

et al. 2023

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We present orbit classification schemes for use as fast metrics for fusion alpha particle losses implemented in the symplectic guiding-centre code SIMPLE. Two variants respectively based on conservation of the parallel adiabatic invariant, and topology of footprints in Poincaré sections are introduced. Like an existing approach based on the Minkowski fractal dimension, those methods estimate whether a guiding-centre orbit is regular and therefore expected to be confined for infinite time in the collisionless case, or chaotic, which might lead to its loss. Compared with the existing approach, the required orbit tracing time for the novel classifiers is shorter by at least an order of magnitude. This enables massive sampling of orbits across the whole phase space to identify regular and chaotic regions for the purpose stellarator optimization. Based on conservation of the perpendicular invariant, we demonstrate how extended regular regions may act as radial barriers for orbits from the chaotic regions on the radially inboard side. We propose to use a quantified version of this property as a new metric for collisionless fusion alpha losses. As pitch-angle scattering becomes only relevant after alphas have already deposited a significant fraction of their energy, such a metric remains useful also for the case with collisions. This is illustrated by comparison with collisional loss computations. Results are presented for applications to two quasi-isodynamic configurations, a quasi-helical configuration and two quasi-axisymmetric configurations. In addition, the Hamiltonian action-angle formalism is used in quasi-axisymmetric configurations to investigate the overlap of drift-orbit resonances leading to chaos. The respective analysis is performed with the NEO-RT code originally developed for investigation of neoclassical toroidal viscous torque in tokamak plasmas.

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“…2019; Velasco et al. 2021) to reduce computational costs. Importantly, recent work by Landreman & Paul (2022) demonstrates that quasiaxisymmetric (QAS) and quasihelically symmetric (QHS) configurations with excellent collisionless alpha confinement are within reach.…”

Section: Introductionmentioning

confidence: 99%

Merging of the superbanana plateau and transport regimes in nearly quasisymmetric stellarators

2023

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Alpha particle confinement is one of the most demanding issues for stellarators. It now seems clear that it is possible to design optimized stellarators that confine the background plasma at near tokamak radial transport levels. Moreover, adequate collisionless alpha particle confinement is possible in the core of a highly optimized stellarator. Here, the collisional confinement of barely trapped alphas in an optimized stellarator is considered by accounting for the resonance due to the reversal in direction of the drift within a flux surface and investigating the sensitive role of magnetic shear in keeping this resonance close to the passing boundary in some nearly quasisymmetric stellarator configurations. The treatment relies on a narrow collisional boundary layer formulation that combines the responses of both these resonant pitch angle alphas and the remaining barely trapped alphas. A novel merged regime treatment leads to explicit expressions for the energy diffusivity for both superbanana plateau (or resonant plateau) and $\sqrt \nu$ transport in the large aspect ratio limit for a slowing down tail alpha distribution function, where $\nu$ is the effective pitch angle scattering collision frequency of the trapped alphas off the background ions. Depending on the details of the optimization scheme and the sign of the magnetic shear, modest magnetic shear can be used to reduce superbanana (or resonant) plateau transport to below the $\sqrt \nu$ transport level. In addition, a quasilinear equation retaining spatial diffusion is derived for a general alpha distribution function that allows the radial alpha transport to modify the distribution so it is no longer isotropic in velocity space.

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A model for the fast evaluation of prompt losses of energetic ions in stellarators

Cited by 14 publications

References 33 publications

Constructing precisely quasi-isodynamic magnetic fields

Constructing precisely quasi-isodynamic magnetic fields

Alpha particle confinement metrics based on orbit classification in stellarators

Merging of the superbanana plateau and transport regimes in nearly quasisymmetric stellarators

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