Theoretical investigation of the triggering of neoclassical tearing modes by transient resonant magnetic perturbations in NSTX

The extended perturbed equilibrium code asymptotic matching code is used to simulate the triggering of n = 1 neoclassical tearing modes (NTMs) by a pulsed, rotating, n = 1, resonant magnetic perturbation (RMP) in two example NSTX discharges. Although the two discharges are significantly different fr...

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Bibliographic Details
Published in:Physics of plasmas 2023-07, Vol.30 (7)
Main Authors: Fitzpatrick, R., Maingi, Rajesh, Park, Jong-Kyu, Sabbagh, Steve
Format: Article
Language:English
Subjects:
70 PLASMA PHYSICS AND FUSION TECHNOLOGY
Deuterium
Discharge
Magnetic fields
Magnetic islands
Perturbation
Plasma confinement
Plasma instabilities
Plasma physics
Plasma properties and parameters
Plasma waves
Pulse amplitude
Pulse duration
Resonant frequencies
Rotation
Tearing
Tearing modes (plasmas)
Tokamaks
Torque
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Summary:The extended perturbed equilibrium code asymptotic matching code is used to simulate the triggering of n = 1 neoclassical tearing modes (NTMs) by a pulsed, rotating, n = 1, resonant magnetic perturbation (RMP) in two example NSTX discharges. Although the two discharges are significantly different from one another, the results of the two sets of simulations are quite similar. The critical n = 1 RMP pulse amplitude required to trigger an n = 1 NTM is minimized when the RMP pulse rotation frequency matches the linear natural frequency of an n = 1 tearing mode, resonant within the plasma, that is metastable to an NTM. However, if there is a frequency mismatch, then the seed magnetic island chain driven at the relevant resonant surface is forced to rotate with respect to the RMP, because the RMP pulse amplitude is nowhere near sufficient to lock the island chain to the RMP. This rotation causes the critical RMP pulse amplitude required to trigger an NTM to oscillate as the RMP pulse duration is varied. The critical amplitude is minimized when the RMP pulse duration is such that seed island chain executes a half-integer number of rotations with respect to the pulse. All of the minima have the same value.
ISSN:1070-664X
1089-7674
DOI:10.1063/5.0155038