The influence of mode coupling on the non-linear evolution of tearing modes

Nave, M. F. F.; Coelho, R.; Lazzaro, E.; Serra, F.

doi:10.1007/s100530050038

Cited by 13 publications

(13 citation statements)

References 16 publications

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“…In the rhs of eq.2 the ′ ∆ 0k tearing stability parameter in general must be assumed to have the expression appropriate for the helical pitch considered, and the remaining terms describe the conventional neo-classical bootstrap term, the ion polarization current term, and the resistive wall term [9].…”

Section: -Experimental Observations and Theoretical Modelmentioning

confidence: 99%

“…In the right-hand side of equation ( 2) the | 0k | tearing stability parameter in general must be assumed to have the expression appropriate for the helical pitch considered, and the remaining terms describe the conventional neo-classical bootstrap term, the ion polarization current term, and the resistive wall term [12]. The driving mode (m = 1, n = 1) grows non-linearly to sufficiently large amplitude driven by its own free energy, with an unperturbed rate of the type…”

Section: Three-mode Non-linear Couplingmentioning

confidence: 99%

“…If the sawtooth crash itself is a doubtful direct triggering mechanism, the data on the other hand suggests that electrodynamic mode coupling [12][13][14] may play an important role in the destabilization of these modes. The (m = 3, n = 2) mode could be driven unstable by toroidal coupling with the n = 2 component of the sawtooth precursor as suggested in [3,7,16].…”

Section: Introductionmentioning

confidence: 99%

“…Therefore, we present a discussion in general terms of the conditions and the effectiveness of mode coupling in perturbing a marginally stable situation. We consider in particular the basic toroidal [12] and non-linear [13,14] coupling mechanisms affecting marginal stability of NTMs. (For simplicity, the non-linear 'pressure driven' interaction between NTMs [15] will be considered small or negligible.)…”

Section: Introductionmentioning

confidence: 99%

“…If the crash itself is a doubtful direct triggering mechanism, the data on the other hand suggests that electro-dynamic mode coupling [9][10][11] may play an important role in the destabilisation of these modes [3,12]. In [3] it was proposed that the (m=3, n=2) modes observed in JET discharges may be destabilized by toroidal coupling with the (m=2, n=2) sawtooth precursor.…”

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confidence: 99%

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Triggering of neo-classical tearing modes by mode coupling

Nave¹,

Lazzaro

Coelho

et al. 2003

Nucl. Fusion

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The formation of magnetic islands with mode numbers (m>1,n=1) apparently triggered by sawtooth crashes has for a long time been a concern in JET discharges with auxiliary heating as it affects the peak performance, in terms of stored energy or of neutron yield (in DT experiments). The phenomenological association of the sawtooth crash with the onset of resistive modes is becoming particularly relevant in the context of Neoclassical Tearing Modes (NTM) theory that requires the formation of a "seed" island above a critical value. Relying on observations and on a critique of the assumed role of the collapse phase of the (1,1) instability we propose as physical mechanism of destabilisation of the metastable NTM a forced reconnection process due to electro-dynamic mode-mode coupling. For specific frequency matching conditions a bifurcation pattern appears in the ∆(W) plot. Modeling of a JET discharge shows that for perfectly frequency matching conditions the triggering of the (m=3, n=2) NTM could be due to either two-mode toroidal coupling or threemode non-linear coupling. The observed mode frequencies are consistent with the non-linear coupling. 1-Introduction In several experiments performed at JET, the peak performance, in terms of neutron yield and plasma stored energy, has been observed to deteriorate in coincidence with the onset of fast

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Section: -Experimental Observations and Theoretical Modelmentioning

confidence: 99%

Section: Three-mode Non-linear Couplingmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

mentioning

confidence: 99%

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Triggering of neo-classical tearing modes by mode coupling

Nave¹,

Lazzaro

Coelho

et al. 2003

Nucl. Fusion

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Bifurcation of generic metastable tearing modes interacting with resonant magnetic fields

Coelho

Lazzaro²

2004

Physics of Plasmas

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The response of generic metastable tearing modes (of which neoclassical tearing modes—NTMs—are a particular example) to resonant external magnetic fields, in rotating tokamak fusion plasmas, is analyzed. In particular, the problem of the bifurcation process that may arise during the driven destabilization of the mode by the external fields is addressed. The results presented provide a clear picture of both the mode amplitude and frequency dynamics in a scenario where there is a differential rotation between the rotating plasma and the external fields. It is shown that the mode frequency exhibits a highly oscillatory behavior during the bifurcation process (owing to the differential rotation) and not a smooth transition between the driving frequency and natural mode rotation. On such grounds, the interpretation of experimental results where magnetic coupling is thought to play a role on the destabilization of some NTMs is revised.

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Phase-locking of magnetic islands diagnosed by ECE-imaging

Tobias

Grierson

Muscatello

et al. 2014

Review of Scientific Instruments

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Millimeter-wave imaging diagnostics identify phase-locking and the satisfaction of 3-wave coupling selection criteria among multiple magnetic island chains by providing a localized, internal measurement of the 2D power spectral density, S(ω, kpol). In high-confinement tokamak discharges, these interactions impact both plasma rotation and tearing stability. Nonlinear coupling among neoclassical tearing modes of different n-number, with islands not satisfying the poloidal mode number selection criterion ⟨m, m('), m - m(')⟩, contributes to a reduction in core rotation and flow shear in the vicinity of the modes.

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The influence of mode coupling on the non-linear evolution of tearing modes

Cited by 13 publications

References 16 publications

Triggering of neo-classical tearing modes by mode coupling

Triggering of neo-classical tearing modes by mode coupling

Bifurcation of generic metastable tearing modes interacting with resonant magnetic fields

Phase-locking of magnetic islands diagnosed by ECE-imaging

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