Sawtooth oscillation behavior with varying amounts of applied stellarator rotational transform

Herfindal, J. L.; Maurer, D.A.; Hartwell, G.J.; Ennis, D.A.; Hanson, J.D.; Knowlton, S.; Ma, X.; Pandya, M. D.; Roberds, Nicholas; Traverso, P.

doi:10.1063/1.5080242

Cited by 4 publications

(15 citation statements)

References 29 publications

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“…The aforementioned forward cascade may be related to the increased linear growth with 3D shaping, as reported by Herfindal et al. (2019) and Roberds et al. (2016).…”

Section: Discussionmentioning

confidence: 56%

“…The decrease of the sawtooth period for increased levels of 3D shaping has been experimentally observed (Herfindal et al. 2019) and computationally verified (Roberds et al. 2016).…”

Section: Magnetic Field Topology During Sawtooth Oscillationsmentioning

confidence: 76%

“…This section summarises experimental (Herfindal et al. 2019) and computational (Roberds et al. 2016) work that evaluates the effect of 3D shaping on sawtooth simulations in CTH.…”

Section: Sawtooth Oscillations In Cthmentioning

confidence: 99%

“…Herfindal et al. (2019) have performed a systematic study of the effects of 3D shaping on CTH sawtooth oscillations by varying the fractional rotational transform in the range. The configurations have tokamak-like profiles for the safety factor, with an on-axis safety factor around unity that monotonically increases to an edge value between 1.6 and 5.…”

Section: Sawtooth Oscillations In Cthmentioning

confidence: 99%

“…Experiments show a reduction in the sawtooth amplitude and an increase in the sawtooth period as is increased (Herfindal et al. 2019). The latter observation is computationally reproduced in Roberds et al.…”

Section: Introductionmentioning

confidence: 99%

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Power-transfer and fixed-point analysis of sawtooth simulations of a current-carrying stellarator

et al. 2022

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Power-transfer and fixed-point analysis of previous NIMROD simulations (Roberds et al., Phys. Plasmas, vol. 23, issue 9, 2016, 092513) improved the understanding of the effect of 3D (non-axisymmetric equilibrium) magnetic fields on sawtooth oscillations in the Compact Toroidal Hybrid (CTH) experiment. Computing the locations of order-1 fixed points, their Greene's residues, and local values for the rotational transform results in a description of CTH sawteeth consistent with Kadomtsev's model. A power-transfer analysis quantifies the distribution of energy among toroidal Fourier modes and their nonlinear interactions. The Lorentz power transfer drives sawtooth growth, and it is unambiguously interpreted as the flow of energy from toroidal mode $n'$ to mode $n$ , catalysed by $\boldsymbol {B}_{n-n'}$ . It has been reported previously that the CTH sawtooth frequency increases with the 3D field strength. This is attributed to an increased growth rate of the internal kink that drives sawtooth oscillations. Here, 3D fields remove energy from the kink, eliminating the possibility that these fields are an additional energy source that drives growth. Instead, 3D fields catalyse energy transfer from large-to-small scales, where magnetic reconnection is stronger. It is proposed that this energy transfer increases the reconnection rate at small scales, which is consistent with the increased growth rate observed at higher 3D field strengths.

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“…The aforementioned forward cascade may be related to the increased linear growth with 3D shaping, as reported by Herfindal et al. (2019) and Roberds et al. (2016).…”

Section: Discussionmentioning

confidence: 56%

“…The decrease of the sawtooth period for increased levels of 3D shaping has been experimentally observed (Herfindal et al. 2019) and computationally verified (Roberds et al. 2016).…”

Section: Magnetic Field Topology During Sawtooth Oscillationsmentioning

confidence: 76%

“…This section summarises experimental (Herfindal et al. 2019) and computational (Roberds et al. 2016) work that evaluates the effect of 3D shaping on sawtooth simulations in CTH.…”

Section: Sawtooth Oscillations In Cthmentioning

confidence: 99%

Section: Sawtooth Oscillations In Cthmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Power-transfer and fixed-point analysis of sawtooth simulations of a current-carrying stellarator

et al. 2022

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Simulating fusion alpha heating in a stellarator reactor

Lazerson

LeViness

Lion

2021

Plasma Phys. Control. Fusion

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Gyrocenter following simulations of fusion born alpha particles in a stellarator reactor are preformed using the BEAMS3D code. The Wendelstein 7-X high mirror configuration is scaled in geometry and magnetic field to reactor relevant parameters. A 2 × 10 20 m−3 density plasma with 20 keV core temperatures is assumed and fusion birth rates calculated for various fusion products assuming a 50/50 deuterium-tritium mixture. It is found that energetic He4 ions comprise the vast majority of the energetic particle inventory. Slowing down simulations of the He4 population suggest plasma heating consistent with scaled energy confinement times for a stellarator reactor. Losses for this configuration appear large suggesting optimization beyond the scope of the W7-X device is key to a future fusion reactor. These first simulations are designed to demonstrate the capability of the BEAMS3D code to provide fusion alpha birth and heating profiles for stellarator reactor designs.

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Model for current drive induced crash cycles in W7-X

et al. 2021

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In the Wendelstein 7-X (W7-X) stellarator, the vacuum rotational transform, ι, has a flat radial profile and does not cross any major rational resonance. Nevertheless, during plasma operation the ι‐profile can be strongly modified by electron cyclotron current drive in such a way that the resulting ι-profile passes through low-order rational values, and this can trigger magnetohydrodynamic (MHD) events. Indeed, W7-X plasmas are sometimes subject to repetitive collapses of core confinement, which can be observed regardless of the direction in which the EC current is driven. Even though the origin of these MHD instabilities is under investigation, the crashes may be connected to the formation of magnetic islands and magnetic reconnection. In the present work, we try to shed light on the dynamics of different events happening during the course of sawtooth cycles in W7-X by proposing a model that combines a slow current diffusion with a recipe for fast relaxation that conserves the corresponding helical flux (Kadomtsev 1975 Fiz. Plazmy 1 710–15). We also propose a simple model based on Taylor relaxation (Taylor 1974 Phys. Rev. Lett. 33 1139), (Taylor 1986 Rev. Mod. Phys. 58 741) to predict the nonlinear redistribution of plasma current caused by the largest of the observed events.

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Sawtooth oscillation behavior with varying amounts of applied stellarator rotational transform

Cited by 4 publications

References 29 publications

Power-transfer and fixed-point analysis of sawtooth simulations of a current-carrying stellarator

Power-transfer and fixed-point analysis of sawtooth simulations of a current-carrying stellarator

Simulating fusion alpha heating in a stellarator reactor

Model for current drive induced crash cycles in W7-X

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