Determination of error field sources by accurate mapping of the magnetic geometry of the H-1 heliac

Kumar, S. T. A.; Blackwell, Boyd; Harris, J. H.

doi:10.1088/0029-5515/49/3/035001

Cited by 7 publications

(6 citation statements)

References 23 publications

(42 reference statements)

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“…The improved coil model indicated strong changes in the magnetic well profile near the edge of the plasma. [13] In the Columbia Non-neutral Torus (CNT) flux surface measurements were used to directly calculate the displacements of the coils [14]. It was later confirmed through numerical simulations that these displacements were consistent with those most likely to influence plasma shape [15].…”

Section: Introductionmentioning

confidence: 95%

Error fields in the Wendelstein 7-X stellarator

Lazerson

Bozhenkov

Israeli

et al. 2018

Plasma Phys. Control. Fusion

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The role of error fields in stellarators is explored in this work through simulations of and experiments performed on the Wendelstein 7-X (W7-X) stellarator. Previous experimental results, based on limiter plasmas in W7-X, suggest that error fields are small in the experiment based on limiter plasmas. In this work, we document results from the first divertor campaign on W7-X with a focus on error fields resonant with the edge island divertor structure. Divertor thermocouples measurements corroborate earlier limiter results that the error fields are small and correctible, requiring only 5% the total rated current of the trim coil system. The effect of these error fields on magnetic geometry and topology are investigated using the technique of flux surface measurement. The resulting divertor thermal load asymmetry is modeled via field line diffusion and compared to experimental data.

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Section: Introductionmentioning

confidence: 95%

Error fields in the Wendelstein 7-X stellarator

Lazerson

Bozhenkov

Israeli

et al. 2018

Plasma Phys. Control. Fusion

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“…This allows systematic control of the rotational transform profile [16]. Vacuum mapping of flux surfaces and islands has been carried out using electron beam wire tomography [17] which enabled accurate determination of H-1NF magnetic geometry [18].…”

Section: Methodsmentioning

confidence: 99%

Spontaneous transition of core radial electric field driven by magnetic islands in the H-1NF heliac

Kumar¹,

Blackwell²,

Howard³

et al. 2011

Nucl. Fusion

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This paper reports an experimental observation of spontaneous transition of the core radial electric field to a large positive value (E r ∼ 5 kV m−1), with a strong electric-field shear (∼700 kV m−2) in a low temperature (T e ∼ 10 eV) radio frequency generated argon plasma in the H-1NF heliac stellarator. The transition, which seems to be driven by a spontaneous excitation of m = 2 magnetic islands near the core, is associated with a localized increase in the plasma density and excitation of coherent low frequency (∼3 kHz) oscillations possibly due to unstable E r shear driven modes. Evidence suggests development of the core electron-root scenario, which previously has been observed only at high temperature electron cyclotron heated plasmas.

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“…The vacuum ι has been corrected by −0.55% to account for the reduction of ι at high fields (B = 0.5T) as reported in [16]. The vacuum magnetic field model for H-1 has been refined based on extensive electron beam mapping at lower magnetic fields [29].…”

Section: Effect Of Rotational Transform On Densitymentioning

confidence: 99%

“…The vacuum magnetic field model for H-1 has been refined based on extensive electron beam mapping at lower magnetic fields [29].…”

Section: Effect Of Rotational Transform On Densitymentioning

confidence: 99%

Influence of magnetic configuration on edge turbulence and transport in the H-1 Heliac

Michael¹,

Zhao²,

Blackwell³

et al. 2016

Plasma Phys. Control. Fusion

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The role of the rotational transform (ι) profile on fluctuations and transport is investigated in the H-1 Heliac by means of dynamic (i.e. changing during a shot) and static (fixed during a shot) scans of rotational transform through a range of values where the electron density drops markedly and which correspond to having the point of ιmin located near r/a = 0.75 in a region of magnetic well (such that the surface averaged magnetic field strength increases with radius). The gap is near the ι = 4/3 resonance, but as the resonance is not in the plasma for more than half the gap it is not clear that this is relevant. Although this drop is clearly driven by the variation of helical current, under particular circumstances, similar density changes occur spontaneously. Plasma currents are measured throughout the scan and are found to slightly affect the rotational transform profile, and reverse about the configuration of minimum confinement, whilst induced currents through a toroidal loop voltage in the dynamical scans are not found to be significant. The confinement and fluctuation properties are studied by means of 2D movable Langmuir probes. Large near edge-localised dithering quasi-coherent fluctuations at ∼ 6 kHz develop in a strong density gradient region with low magnetic shear as ι is scanned up to a point where the density collapses in the outer region. This dithering corresponds to an m=3 mode comprising of standing and propagating components. The net and fluctuation-induced transport components are measured near the plasma edge in a similar discharge, and it is found that fluctuation-induced transport driven by these low frequency coherent modes dominates the particle balance during the low density phase but is only a small component of the net flux when the density is higher.

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Determination of error field sources by accurate mapping of the magnetic geometry of the H-1 heliac

Cited by 7 publications

References 23 publications

Error fields in the Wendelstein 7-X stellarator

Error fields in the Wendelstein 7-X stellarator

Spontaneous transition of core radial electric field driven by magnetic islands in the H-1NF heliac

Influence of magnetic configuration on edge turbulence and transport in the H-1 Heliac

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