Observation of a new toroidally localized kink mode and its role in reverse-field<i>–</i>pinch plasmas

Tamano, T.; Bard, W.D.; Chu, C. K.; Kondoh, Yasumitsu; Haye, R.J. La; Lee, Paul S.; Saito, M.T.; Schaffer, M. J.; Taylor, P.L.

doi:10.1103/physrevlett.59.1444

Cited by 86 publications

(43 citation statements)

References 5 publications

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“…This behavior is reminiscent of the socalled "slinky mode" generated by the nonlinear phase locking of tearing modes in reversed-field pinches. [39][40][41][42] V. TOROIDAL COUPLING OF TWO NEOCLASSICAL TEARING MODES…”

Section: Phase-locked Statementioning

confidence: 99%

Phase locking of multi-helicity neoclassical tearing modes in tokamak plasmas

Fitzpatrick¹

2015

Physics of Plasmas

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The attractive "hybrid" tokamak scenario combines comparatively high q 95 operation with improved confinement compared with the conventional H 98;y2 scaling law. Somewhat unusually, hybrid discharges often exhibit multiple neoclassical tearing modes (NTMs) possessing different mode numbers. The various NTMs are eventually observed to phase lock to one another, giving rise to a significant flattening, or even an inversion, of the core toroidal plasma rotation profile. This behavior is highly undesirable because the loss of core plasma rotation is known to have a deleterious effect on plasma stability. This paper presents a simple, single-fluid, cylindrical model of the phase locking of two NTMs with different poloidal and toroidal mode numbers in a tokamak plasma. Such locking takes place via a combination of nonlinear three-wave coupling and conventional toroidal coupling. In accordance with experimental observations, the model predicts that there is a bifurcation to a phase-locked state when the frequency mismatch between the modes is reduced to one half of its original value. In further accordance, the phase-locked state is characterized by the permanent alignment of one of the X-points of NTM island chains on the outboard midplane of the plasma, and a modified toroidal angular velocity profile, interior to the outermost coupled rational surface, which is such that the core rotation is flattened, or even inverted. V C 2015 AIP Publishing LLC. [http://dx.

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Section: Phase-locked Statementioning

confidence: 99%

Phase locking of multi-helicity neoclassical tearing modes in tokamak plasmas

Fitzpatrick¹

2015

Physics of Plasmas

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“…13 Moreover, the tearing modes generally lock in phase together, generating a toroidally localized strong magnetic perturbation, commonly called the "slinky" mode. 14,15 When the modes also lock to the wall, the slinky-wall interaction is increased, producing influx of wall impurities. 16,17 Instead, in the theoretically predicted single helicity ͑SH͒ regime, the dynamo is produced by the interaction of a single tearing mode with the velocity field produced by an electrostatic drift due to a small charge separation; 18 the SH plasma core is characterized by a magnetic island generated by the single mode and has no magnetic chaos.…”

Section: Introductionmentioning

confidence: 99%

Spontaneous quasi single helicity regimes in EXTRAP T2R reversed-field pinch

et al. 2007

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In recent years, good progress toward a better understanding and control of the plasma performance in reversed-field pinch devices has been made. These improvements consist both of the discovery of spontaneous plasma regimes, termed the quasi single helicity ͑QSH͒ regime, in which part of the plasma core is no longer stochastic, and of the development of techniques for active control of plasma instabilities. In this paper, a systematic study of spontaneous QSH in the EXTRAP T2R device ͓P. R. Brunsell, H. Bergsaker, M. Cecconello et al., Plasma Phys. Control. Fusion 43, 1457 ͑2001͔͒ is presented. In this device, QSH states can occur spontaneously and it is associated with magnetic and thermal structures. A statistical analysis to determine the most favorable experimental conditions to have a transition to the QSH regime will be presented. The results described here are useful to understand the underlying properties of QSH regimes in view of future applications of the QSH active control in EXTRAP T2R; they are also important to have a comparison with the QSH studied in other devices.

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“…[6][7][8] This mode degrades the plasma confinement, giving rise to a rotating, toroidally localized ''hot spot'' on the plasma facing surface. Slinky modes sometimes lock to static error fields, and, thereby, stop rotating in the laboratory frame.…”

Section: Introductionmentioning

confidence: 99%

Formation and locking of the “slinky mode” in reversed-field pinches

Fitzpatrick

1999

Physics of Plasmas

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The formation and breakup of the ''slinky mode'' in a Reversed-Field Pinch ͑RFP͒ is investigated analytically. The slinky mode is a toroidally localized, coherent interference pattern in the magnetic field, which corotates with the plasma at the reversal surface. This mode forms, via a series of bifurcations, as a result of the nonlinear coupling of multiple mϭ1 core tearing modes. The slinky mode breaks up via a second series of bifurcations. However, the typical mode amplitude below which slinky breakup is triggered is much smaller than that above which slinky formation occurs. Analytic expressions for the slinky formation and breakup thresholds are obtained in all regimes of physical interest. The locking of the slinky mode to a static error field is also investigated analytically. Either the error field arrests the rotation of the plasma at the reversal surface before the formation of the slinky mode, so that the mode subsequently forms as a nonrotating mode, or the slinky mode forms as a rotating mode and subsequently locks to the error field. Analytic expressions for the locking and unlocking thresholds are obtained in all regimes of physical interest.

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Observation of a new toroidally localized kink mode and its role in reverse-field–pinch plasmas

Cited by 86 publications

References 5 publications

Phase locking of multi-helicity neoclassical tearing modes in tokamak plasmas

Phase locking of multi-helicity neoclassical tearing modes in tokamak plasmas

Spontaneous quasi single helicity regimes in EXTRAP T2R reversed-field pinch

Formation and locking of the “slinky mode” in reversed-field pinches

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