The effects of non-uniform drive on plasma filaments

Shanahan, B.; Dudson, B.; Hill, P.

doi:10.1088/1742-6596/1125/1/012018

Cited by 8 publications

(16 citation statements)

References 12 publications

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“…A filament dipole -and therefore the electric field which drives motion -is created due to diamagnetic drifts (curvature and ∇B). Acknowledging previous work (Shanahan et al 2018) which indicated that this curvature drive could be approximated as an average curvature, we see that the large aspect ratio of Wendelstein 7-X leads to a small polarizing force. This effect is somewhat mitigated by the large connection lengths of the W7-X island divertor topology.…”

Section: Discussionsupporting

confidence: 70%

“…Simulations of blobs in slab geometries are common (D 'Ippolito & Myra 2003;D'Ippolito et al 2004;Aydemir 2005;Garcia et al 2005;Garcia, Bian & Fundamenski 2006;Myra, Russell & D'Ippolito 2006;Riva et al 2016;Shanahan & Dudson 2016;Walkden et al 2016) since these simulations are much faster than global edge simulations, allowing thorough investigations of the primary mechanisms in filament dynamics. This method has already been applied to non-uniform drive scenarios (Shanahan, Dudson & Hill 2018), a feature which is prominent in -but not exclusive to -stellarators. In Shanahan et al (2018) it was determined that a filament which is driven by non-uniform curvature will, on average, propagate as if driven by the field-line-averaged curvature -except in cases of highly non-uniform drive.…”

Section: Introductionmentioning

confidence: 99%

“…This method has already been applied to non-uniform drive scenarios (Shanahan, Dudson & Hill 2018), a feature which is prominent in -but not exclusive to -stellarators. In Shanahan et al (2018) it was determined that a filament which is driven by non-uniform curvature will, on average, propagate as if driven by the field-line-averaged curvature -except in cases of highly non-uniform drive. Additionally, it was determined by Killer et al (2020) that simulations in drift-plane geometries effectively recover the macroscopic transport dynamics of filaments measured in experiment.…”

Section: Introductionmentioning

confidence: 99%

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Filament simulations in regions of highly-varying parallel connection length

Shanahan

Huslage²

2020

J. Plasma Phys.

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The island divertor topology of the Wendelstein 7-X (W7-X) scrape-off-layer exhibits regions of highly varying connection length. Here, we present drift-plane simulations of seeded filaments in regions of sharp transitions in parallel connection length – a parameter which dictates the propagation regime for plasma blobs. It is determined that a transition in parallel connection length alters the trajectory of filaments; filaments which enter regions of lower connection length are decelerated, and vice versa. It is also determined that if the lobes of a potential dipole created by diamagnetic drifts within the filament exist in two regions of distinct parallel connection length, the filament is then steered towards the region of higher connection length. The extreme case of a narrow region of varying connection length can also alter the trajectory of a filament, depending on the extent of this region. Finally, simulations mimicking the view from the W7-X gas puff imaging (GPI) diagnostic view plane are presented. It is determined that filaments in the view of the W7-X GPI diagnostic exhibit a predominantly poloidal propagation due to the radial electric field, since the radial velocity is relatively small.

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Section: Discussionsupporting

confidence: 70%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Filament simulations in regions of highly-varying parallel connection length

Shanahan

Huslage²

2020

J. Plasma Phys.

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“…While the normal curvature in W7-X has strong, fine-scale variations along a magnetic flux tube [14,28], previous work has indicated that due to the fast dynamics parallel to the ambient magnetic field, the averaged normal curvature along a field line dominates the formation and behaviour of turbulent filaments [14,29]. Since the magnetic configurations of W7-X considered here mostly differ with respect to the rotational transform, the magnetic curvature profile along a field line starting from the probe does not change more than a few % between configurations.…”

Section: Magnetic Field Characteristicsmentioning

confidence: 99%

Turbulent transport in the scrape-off layer of Wendelstein 7-X

2021

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Turbulent transport is widely considered to be the main driver for cross-field transport in the scrape-off layer (SOL) of toroidal magnetized plasmas. Here, reciprocating Langmuir probes are employed to measure both the plasma profiles and the turbulent particle transport in the SOL of the Wendelstein 7-X stellarator. The relation between turbulent radial particle flux Γ r and the local pressure gradient is often approximately linear across the entire SOL width, indicating that radial turbulence spreading is absent. This observation holds across a wide range of magnetic configurations and different plasma heating and density scenarios. The magnitude of the turbulent transport for a given gradient reveals a dependence on the magnetic configuration and the position in the SOL, which we relate to the cross-spectral characteristics of multi-tip floating potential measurements. Magnetic islands can add further complexity due to non-monotonic SOL profiles and the breaking of the transport-gradient relation. Finally, anomalous diffusion coefficients are determined from the probe measurements.

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“…Such environment for filaments is just starting to be addressed with simulations [10]. Numerical studies [11] claim that filaments can exist and propagate outward in the presence of a nonuniform curvature drive as long as the field-line averaged curvature is negative. This behaviour is enabled by the high conductivity along the field lines which effectively averages polarization.…”

Section: Introductionmentioning

confidence: 99%

Statistical analysis of plasma filaments in the island divertor of Wendelstein 7-X

Csillag,

Zoletnik,

Killer

et al. 2023

Nucl. Fusion

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Plasma filaments have been measured with alkali beam emission spectroscopy in the plasma edge, divertor island, and scrape-off layer of Wendelstein 7-X. Due to the high intensity of a 1–2 kHz plasma mode, a new, correlation based conditional averaging algorithm was used to search for filaments in the signals. With that method, effects of different magnetic configurations and density levels on filament properties are observed. In configurations where the islands are small and do not play an important role for the connection length topology, filaments behave similar to tokamaks. In contrast, in configurations with larger magnetic islands and more complex connection length profiles, filaments behave quite differently, for instance they may or may not appear in the inner side of the divertor island depending on the plasma parameters. Coupling between the filaments and lower frequency events are also showed. The role of filaments in the global and local particle transport is briefly discussed.

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The effects of non-uniform drive on plasma filaments

Cited by 8 publications

References 12 publications

Filament simulations in regions of highly-varying parallel connection length

Filament simulations in regions of highly-varying parallel connection length

Turbulent transport in the scrape-off layer of Wendelstein 7-X

Statistical analysis of plasma filaments in the island divertor of Wendelstein 7-X

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