Active Stabilization of the Resistive-Wall Mode in High-Beta, Low-Rotation Plasmas

Sabbagh, S.A.; Bell, R. E.; Ménard, J.; Gates, D.; Sontag, A. C.; Bialek, J.; LeBlanc, B.; Levinton, F. M.; Tritz, K.; Yuh, H.

doi:10.1103/physrevlett.97.045004

Cited by 127 publications

(134 citation statements)

References 23 publications

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“…in a 'compass scan') to determine the optimum EF correction for locked mode avoidance over a sequence of shots. Very low-frequency and locked modes are detected using a low-field-side toroidal array of radial and PF sensors [8,37,38].…”

Section: Macroscopic Stabilitymentioning

confidence: 99%

Overview of NSTX Upgrade initial results and modelling highlights

Ménard¹,

Allain²,

Battaglia³

et al. 2017

Nucl. Fusion

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The National Spherical Torus Experiment (NSTX) has undergone a major upgrade, and the NSTX Upgrade (NSTX-U) Project was completed in the summer of 2015. NSTX-U first plasma was subsequently achieved, diagnostic and control systems have been commissioned, the H-mode accessed, magnetic error fields identified and mitigated, and the first physics research campaign carried out. During ten run weeks of operation, NSTX-U surpassed NSTX record pulse-durations and toroidal fields (TF), and high-performance ~1 MA H-mode plasmas comparable to the best of NSTX have been sustained near and slightly above the n = 1 no-wall stability limit and with H-mode confinement multiplier H98y,2 above 1. Transport and turbulence studies in L-mode plasmas have identified the coexistence of at least two ion-gyro-scale turbulent micro-instabilities near the same radial location but propagating in opposite (i.e. ion and electron diamagnetic) directions. These modes have the characteristics of ion-temperature gradient and micro-tearing modes, respectively, and the role of these modes in contributing to thermal transport is under active investigation. The new second more tangential neutral beam injection was observed to significantly modify the stability of two types of Alfven eigenmodes. Improvements in offline disruption forecasting were made in the areas of identification of rotating MHD modes and other macroscopic instabilities using the disruption event characterization and forecasting code. Lastly, the materials analysis and particle probe was utilized on NSTX-U for the first time and enabled assessments of the correlation between boronized wall conditions and plasma performance. These and other highlights from the first run campaign of NSTX-U are described.

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Section: Macroscopic Stabilitymentioning

confidence: 99%

Overview of NSTX Upgrade initial results and modelling highlights

Ménard¹,

Allain²,

Battaglia³

et al. 2017

Nucl. Fusion

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“…10, an example of the rapid progress made in this area is shown, where the n ¼ 1 resistive wall mode instability, which normally causes plasmas to terminate (particularly at low plasma rotation), was stabilized using passive and active feedback. 33 This resulted in the sustainment of a high b N $ 6.0 plasma, which is about 50% above the so-called no wall beta limit even at low plasma rotation in NSTX.…”

Section: A Overviewmentioning

confidence: 99%

Recent progress on spherical torus research

Ono

Kaita

2015

Physics of Plasmas

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The spherical torus or spherical tokamak (ST) is a member of the tokamak family with its aspect ratio (A = R0/a) reduced to A ∼ 1.5, well below the normal tokamak operating range of A ≥ 2.5. As the aspect ratio is reduced, the ideal tokamak beta β (radio of plasma to magnetic pressure) stability limit increases rapidly, approximately as β ∼ 1/A. The plasma current it can sustain for a given edge safety factor q-95 also increases rapidly. Because of the above, as well as the natural elongation κ, which makes its plasma shape appear spherical, the ST configuration can yield exceptionally high tokamak performance in a compact geometry. Due to its compactness and high performance, the ST configuration has various near term applications, including a compact fusion neutron source with low tritium consumption, in addition to its longer term goal of an attractive fusion energy power source. Since the start of the two mega-ampere class ST facilities in 2000, the National Spherical Torus Experiment in the United States and Mega Ampere Spherical Tokamak in UK, active ST research has been conducted worldwide. More than 16 ST research facilities operating during this period have achieved remarkable advances in all fusion science areas, involving fundamental fusion energy science as well as innovation. These results suggest exciting future prospects for ST research both near term and longer term. The present paper reviews the scientific progress made by the worldwide ST research community during this new mega-ampere-ST era.

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“…It has been well-known that even a small magnetic perturbation of order of |δB/B| ∼ 10 −4 can dramatically modify tokamak transport and thereby various macroscopic stabilities such as locked modes, edge localized modes, and resistive wall modes [1][2][3][4].…”

mentioning

confidence: 99%