Adjoint methods for quasi-symmetry of vacuum fields on a surface

Nies, Richard; Paul, Elizabeth; Hudson, S. R.; Bhattacharjee, A.

doi:10.1017/s0022377821001264

Cited by 4 publications

(3 citation statements)

References 47 publications

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“…To further study the mechanisms for the deviations in J , we perform GC integration in several vacuum equilibria that are optimized for quasiaxisymmetry on the boundary [58] in addition to having a value of ι = 0.52 on the boundary and aspect ratio 6. For the base equilibrium, the optimization is terminated when the quasisymmetry on the boundary is f QS = 1.8 × 10 −2 , see (9).…”

Section: Diffusive Banana Transportmentioning

confidence: 99%

Energetic particle loss mechanisms in reactor-scale equilibria close to quasisymmetry

et al. 2022

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Collisionless physics primarily determines the transport of fusion-born alpha particles in 3D equilibria. Several transport mechanisms have been implicated in stellarator configurations, including stochastic diffusion due to class transitions, ripple trapping, and banana drift-convective orbits. Given the guiding center dynamics in a set of six quasihelical and quasiaxisymmetric equilibria, we perform a classification of trapping states and transport mechanisms. In addition to banana drift convection and ripple transport, we observe substantial non-conservation of the parallel adiabatic invariant which can cause losses through diffusive banana tip motion. Furthermore, many lost trajectories undergo transitions between trapping classes on longer time scales, either with periodic or irregular behavior. We discuss possible optimization strategies for each of the relevant transport mechanisms. We perform a comparison between fast ion losses and metrics for the prevalence of mechanisms such as banana-drift convection, transitioning orbits, and wide orbit widths. Quasihelical configurations are found to have natural protection against ripple-trapping and diffusive banana tip motion leading to a reduction in prompt losses.

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Section: Diffusive Banana Transportmentioning

confidence: 99%

Energetic particle loss mechanisms in reactor-scale equilibria close to quasisymmetry

et al. 2022

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“…Figure 1 extends the comparison plot in our earlier paper to include both free boundary and fixed boundary metrics. It includes the 'precise QA' case from (Landreman & Paul 2022;) and a 'compact QA' case from adjoint-optimisation (Nies et al 2022;Nies & Paul 2023). These were both published after the MUSE equilibrium was already selected.…”

Section: Introductionmentioning

confidence: 99%

“…2022) and a ‘compact QA’ case from adjoint-optimisation (Nies et al. 2022; Nies & Paul 2023). These were both published after the MUSE equilibrium was already selected.…”

Section: Introductionmentioning

confidence: 99%

Design and construction of the MUSE permanent magnet stellarator

Qian,

Chu,

Pagano

et al. 2023

J. Plasma Phys.

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This paper documents the design and construction of MUSE, the world's first permanent magnet (PM) stellarator and the first quasi-axisymmetric experiment. The purpose of MUSE is to develop and assess a new way of building optimised stellarators that uses simple planar coils PMs. Our PM optimisation algorithm consists of initialising a geometry to pack dipoles densely, running the FAMUS code to minimise surface field error subject to PM constraints and applying discrete jumps to reach a physically realisable solution. FAMUS treats the PM system as a set of ideal point dipoles. From there we construct finite-volume magnet towers to be housed in 3D-printed PM holders. We describe the design of the PM holders, which were validated by laser metrology. We analyse the effects of finite permeability, sensitivity to perturbations and magnetostatic forces. An exact analytic formula for the magnetic field from a finite-volume PM tower is presented to compute PM–PM forces and stress on the PM holder. Stellarator construction is complete and experiments are underway.

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Exploration of the parameter space of quasisymmetric stellarator vacuum fields through adjoint optimisation

Nies,

Paul,

Panici

et al. 2024

J. Plasma Phys.

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Optimising stellarators for quasisymmetry leads to strongly reduced collisional transport and energetic particle losses compared with unoptimised configurations. Although stellarators with precise quasisymmetry have been obtained in the past, it remains unclear how broad the parameter space is where good quasisymmetry may be achieved. We study the range of aspect ratios and rotational transform values for which stellarators with excellent quasisymmetry on the boundary can be obtained. A large number of Fourier harmonics is included in the boundary representation, which is made computationally tractable by the use of adjoint methods to enable fast gradient-based optimisation and by the direct optimisation of vacuum magnetic fields, which converge more robustly compared with solutions from magnetohydrostatics. Several novel configurations are presented, including stellarators with record levels of quasisymmetry on a surface, three field period quasiaxisymmetric stellarators with substantial magnetic shear, and compact quasisymmetric stellarators at low aspect ratios similar to tokamaks.

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Adjoint methods for quasi-symmetry of vacuum fields on a surface

Cited by 4 publications

References 47 publications

Energetic particle loss mechanisms in reactor-scale equilibria close to quasisymmetry

Energetic particle loss mechanisms in reactor-scale equilibria close to quasisymmetry

Design and construction of the MUSE permanent magnet stellarator

Exploration of the parameter space of quasisymmetric stellarator vacuum fields through adjoint optimisation

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