A new explanation of the sawtooth phenomena in tokamaks

Jardin, S.C.; Krebs, I.; Ferraro, N.M.

doi:10.1063/1.5140968

Cited by 38 publications

(30 citation statements)

References 64 publications

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“…1a without the break-out reconnecting current sheet) can significantly accelerate the erupting filament. Finally, in laboratory magnetic fusion experiments, models of the sawtooth oscillation typically involve driven reconnection of helical flux at a current sheet formed in response to the internal kink instability 188,189 , although other explanations have been proposed 190 .…”

Section: Coupling Of Reconnection To Macroscale Instabilitiesmentioning

confidence: 99%

Magnetic reconnection in the era of exascale computing and multiscale experiments

Ji,

Daughton,

Jara-Almonte

et al. 2022

Preprint

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Astrophysical plasmas have the remarkable ability to preserve magnetic topology, which inevitably gives rise to the accumulation of magnetic energy within stressed regions including current sheets. This stored energy is often released explosively through the process of magnetic reconnection, which produces a reconfiguration of the magnetic field, along with high-speed flows, thermal heating, and nonthermal particle acceleration. Either collisional or kinetic dissipation mechanisms are required to overcome the topological constraints, both of which have been predicted by theory and validated with in situ spacecraft observations or laboratory experiments. However, major challenges remain in understanding magnetic reconnection in large systems, such as the solar corona, where the collisionality is weak and the kinetic scales are vanishingly small in comparison to macroscopic scales. The plasmoid instability or formation of multiple plasmoids in long reconnecting current sheets is one possible multiscale solution for bridging this vast range of scales, and new laboratory experiments are poised to study these regimes. In conjunction with these efforts, we anticipate that the coming era of exascale computing, together with the next generation of observational capabilities, will enable new progress on a range of challenging problems, including the energy build-up and onset of reconnection, partially ionized regimes, the influence of magnetic turbulence, and particle acceleration.Website summary: Magnetic reconnection explosively releases stored magnetic energy in astrophysical plasmas. Thanks to advances in observations, exascale computing and multiscale experiments, it will be possible to solve outstanding physics problems, including the immense separation between global and dissipation scales, reconnection onset, and particle acceleration.

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Section: Coupling Of Reconnection To Macroscale Instabilitiesmentioning

confidence: 99%

Magnetic reconnection in the era of exascale computing and multiscale experiments

Ji,

Daughton,

Jara-Almonte

et al. 2022

Preprint

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“… Kadomtsev (Kadomtsev 1975): 2D (‘2D’ denotes a plasma model that has a two-dimensional poloidal and axisymmetric toroidal description; ‘3D’ denotes a plasma model that is described with three-dimensional geometry), global. Ballooning (Bussac & Pellat 1987; Park et al. 1995): 3D, global and local are possible. Quasi-interchange: Wesson (Wesson & Campbell 2011): 2D, global; Jardin (Jardin, Krebs & Ferraro 2020): 3D, global. Stochastic (Lichtenberg et al. 1992; Igochine et al.…”

Section: Existing Modelsmentioning

confidence: 99%

“…Quasi-interchange: Wesson (Wesson & Campbell 2011): 2D, global; Jardin (Jardin, Krebs & Ferraro 2020): 3D, global.…”

Section: Existing Modelsmentioning

confidence: 99%

Global nature of magnetic reconnection during sawtooth crash in ASDEX Upgrade

et al. 2022

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This paper discusses the toroidal localisation of magnetic reconnection during sawtooth crashes. Numerical analysis with realistic heat diffusion coefficients shows that heat distributes itself helically along the torus faster than the temporal resolution of any existing ECE diagnostics. It makes local and global (helically axisymmetric) magnetic reconnection indistinguishable for an observer, while a local crash where the heat stays confined within a finite helical region could be distinguished. Statistical analysis of sawtooth crashes with the ECEI diagnostic is conducted in ASDEX Upgrade. The displacement of the heat within a finite helical region has not been observed. The statistical data supports global magnetic reconnection.

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“…In the traditional Kadomtsev model 2 , the crash time is related to how fast reconnection can occur to re-arrange the magnetic field. Several possible competing mechanisms have been proposed for the fast crash, including two-fluid effects at the reconnection layer [3][4][5][6] , plasmoid instability [7][8][9] , and interchange instability 10,11 .…”

Section: Introductionmentioning

confidence: 99%

Two-dimensional plasma density evolution local to the inversion layer during sawtooth crash events using Beam Emission Spectroscopy

Bose¹,

Fox²,

Liu³

et al. 2022

Preprint

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We present methods for analyzing Beam Emission Spectroscopy (BES) data to obtain the plasma density evolution associated with rapid sawtooth crash events at the DIII-D tokamak. BES allows coverage over a 2-D spatial plane, inherently local measurements, with fast time responses, and therefore provides a valuable new channel for data during sawtooth events. A method is developed to remove sawtooth-induced edge-light pulses contained in the BES data. The edge light pulses appear to be from the D α emission produced by edge recycling during sawtooth events, and are large enough that traditional spectroscopic filtering and data analysis techniques are insufficient to deduce physically meaningful quantities. A cross-calibration of 64 BES channels is performed using a novel method to ensure accurate measurements. For the large-amplitude density oscillations observed, we discuss and use the non-linear relationship between BES signal δI/I 0 and plasma density variation δn e /n e0 . 2-D BES images cover a 8 cm × 20 cm region around the sawtooth inversion layer and show large-amplitude density oscillations, with additional significant spatial variations across the inversion layer, which grows and peaks near the time of the temperature crash. The edge light removal technique and method of converting large-amplitude δI/I 0 to δn e /n e0 presented here may help analyze other impulsive MHD phenomena in tokamaks.

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A new explanation of the sawtooth phenomena in tokamaks

Cited by 38 publications

References 64 publications

Magnetic reconnection in the era of exascale computing and multiscale experiments

Magnetic reconnection in the era of exascale computing and multiscale experiments

Global nature of magnetic reconnection during sawtooth crash in ASDEX Upgrade

Two-dimensional plasma density evolution local to the inversion layer during sawtooth crash events using Beam Emission Spectroscopy

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