Resistive wall mode and neoclassical tearing mode coupling in rotating tokamak plasmas

Rachel McAdams; H. R. Wilson; I. T. Chapman

doi:10.1088/0029-5515/53/8/083005

Resistive wall mode and neoclassical tearing mode coupling in rotating tokamak plasmas

Rachel McAdams, H. R. Wilson, I. T. Chapman

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3 Scopus citations

Abstract

A model system of equations has been derived to describe a toroidally rotating tokamak plasma, unstable to resistive wall modes (RWMs) and metastable to neoclassical tearing modes (NTMs), using a linear RWM model and a nonlinear NTM model. If no wall is present, the NTM growth shows the typical threshold/saturation island widths, whereas a linearly unstable kink mode grows exponentially in this model plasma system. When a resistive wall is present, the growth of the linearly unstable RWM is accelerated by an unstable island: a form of coupled RWM-NTM mode. Crucially, this coupled system has no threshold island width, giving the impression of a triggerless NTM, observed in high beta tokamak discharges. Increasing plasma rotation at the island location can mitigate its growth, decoupling the modes to yield a conventional RWM with no threshold width.

Original language	English
Article number	083005
Journal	Nuclear Fusion
Volume	53
Issue number	8
DOIs	https://doi.org/10.1088/0029-5515/53/8/083005
State	Published - Aug 2013
Externally published	Yes

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title = "Resistive wall mode and neoclassical tearing mode coupling in rotating tokamak plasmas",

abstract = "A model system of equations has been derived to describe a toroidally rotating tokamak plasma, unstable to resistive wall modes (RWMs) and metastable to neoclassical tearing modes (NTMs), using a linear RWM model and a nonlinear NTM model. If no wall is present, the NTM growth shows the typical threshold/saturation island widths, whereas a linearly unstable kink mode grows exponentially in this model plasma system. When a resistive wall is present, the growth of the linearly unstable RWM is accelerated by an unstable island: a form of coupled RWM-NTM mode. Crucially, this coupled system has no threshold island width, giving the impression of a triggerless NTM, observed in high beta tokamak discharges. Increasing plasma rotation at the island location can mitigate its growth, decoupling the modes to yield a conventional RWM with no threshold width.",

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AU - Chapman, I. T.

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AB - A model system of equations has been derived to describe a toroidally rotating tokamak plasma, unstable to resistive wall modes (RWMs) and metastable to neoclassical tearing modes (NTMs), using a linear RWM model and a nonlinear NTM model. If no wall is present, the NTM growth shows the typical threshold/saturation island widths, whereas a linearly unstable kink mode grows exponentially in this model plasma system. When a resistive wall is present, the growth of the linearly unstable RWM is accelerated by an unstable island: a form of coupled RWM-NTM mode. Crucially, this coupled system has no threshold island width, giving the impression of a triggerless NTM, observed in high beta tokamak discharges. Increasing plasma rotation at the island location can mitigate its growth, decoupling the modes to yield a conventional RWM with no threshold width.

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Resistive wall mode and neoclassical tearing mode coupling in rotating tokamak plasmas

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