Momentum Transport from Nonlinear Mode Coupling of Magnetic Fluctuations

Hansen, A. K.; Almagri, A. F.; Craig, D.; Hartog, D. J. Den; Hegna, C. C.; Prager, S. C.; Sarff, J. S.

doi:10.1103/physrevlett.85.3408

Cited by 38 publications

(34 citation statements)

References 16 publications

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“…28 Between crashes, when mode amplitudes are generally smaller, the coupling is very weak. 28 In this study, we exclude plasmas in which a sawtooth crash occurs during deceleration of the QSH dominant mode. Between crashes in QSH plasmas, as in other standard MST plasmas, the amplitude of the ͑0,1͒ mode is small.…”

Section: B Mode Couplingmentioning

confidence: 98%

“…18,28 This torque is exerted via nonlinear coupling of three modes, one of which is the QSH dominant mode. In contrast to the externally imposed torque due to an error field or eddy currents in the shell, which causes a net loss of plasma angular momentum, the torque from mode coupling results only in a redistribution of momentum internal to the plasma.…”

Section: B Mode Couplingmentioning

confidence: 99%

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Observation of tearing mode deceleration and locking due to eddy currents induced in a conducting shell

et al. 2004

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Growth to large amplitude of a single core-resonant tearing mode in the Madison Symmetric Torus [R. N. Dexter et al., Fusion Technol. 19, 131 (1991)] reversed-field pinch is accompanied by braking and eventual cessation of mode rotation. There is also a concurrent deceleration of bulk plasma rotation. The mode deceleration is shown to be well described by a time-dependent version of a magnetohydrodynamical model [R. Fitzpatrick et al., Phys. Plasmas 6, 3878 (1999)] in which a braking torque originates from eddy currents induced by the rotating mode in the conducting shell surrounding the plasma. According to the model, the electromagnetic braking torque is localized to the plasma in the immediate vicinity of the mode’s resonant surface, but viscosity transfers the torque to the rest of the plasma. Parametrizing the plasma viscous momentum diffusivity in terms of the global momentum confinement time, the model is used to predict both the momentum confinement time and the time evolution of the decelerating mode velocity. In both respects, the model is quite consistent with experimental data.

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Section: B Mode Couplingmentioning

confidence: 98%

Section: B Mode Couplingmentioning

confidence: 99%

Observation of tearing mode deceleration and locking due to eddy currents induced in a conducting shell

et al. 2004

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“…Coupling of two adjacent m = 1 modes via interaction with an m = 0 mode has been shown to be very important in both experiments and MHD computation. [25][26][27] A typical strong three wave interaction observed in MST plasmas is that between the ͑m =1, n =6͒, ͑1,7͒ and ͑0,1͒ modes. By suppressing one of the interacting modes, we can reduce the nonlinear mode coupling.…”

Section: B Origin Of Charge Fluxmentioning

confidence: 98%

Stochastic magnetic field driven charge transport and zonal flow during magnetic reconnection

et al. 2008

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Magnetic fluctuation-induced charge transport, resulting from particle transport that is not intrinsically ambipolar, has been measured in the high-temperature interior of a reversed-field pinch plasma. It is found that global resistive tearing modes and their nonlinear interactions lead to significant charge transport, equivalent to the perpendicular Maxwell stress, in the vicinity of the resonant surface for the dominant core resonant mode during magnetic reconnection. Finite charge transport can result in a zonal flow associated with locally strong radial electric field and electric field shear. In the presence of stochastic magnetic field, radial electric field is expected to be balanced by radial electron pressure gradient. Direct measurement of local density gradient is consistent with the formation of radial electric field and the zonal flow.

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“…3,4 Nevertheless, previous experimental results demonstrate the importance of fully nonlinear effects such as tearing mode saturation and coupling. 5,6 In nonlinear magnetohydrodynamic ͑MHD͒ computations, numeric parameters such as viscosity and pressure often alter the generated flow structure much more than the magnetic dynamics. Flows associated with tearing modes have previously been inferred from E ϫ B measurements, 7 observed in the plasma edge with a spectroscopic probe, 8 and measured in the core with line-integrated spectroscopy.…”

Section: Introductionmentioning

confidence: 99%

Local measurements of tearing mode flows and the magnetohydrodynamic dynamo in the Madison Symmetric Torus reversed-field pinch

et al. 2010

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The first localized measurements of tearing mode flows in the core of a hot plasma are presented using nonperturbing measurements of the impurity ion flow. Emission from charge exchange recombination is collected by a novel high optical throughput duo spectrometer providing localized ͑Ϯ1 cm͒ measurements of C +6 impurity ion velocities resolved to Ͻ500 m / s with high bandwidth ͑100 kHz͒. Poloidal tearing mode flows in the Madison Symmetric Torus reversed-field pinch are observed to be localized to the mode resonant surface with a radial extent much broader than predicted by linear magnetohydrodynamic ͑MHD͒ theory but comparable to the magnetic island width. The relative poloidal flow amplitudes among the dominant core modes do not reflect the proportions of the magnetic amplitudes. The largest correlated flows are associated with modes having smaller magnetic amplitudes resonant near the midradius. The MHD dynamo due to these flows on the magnetic axis is measured to be adequate to balance the mean Ohm's law during reduced tearing activity and is significant but does not exclude other dynamo mechanisms from contributing during a surge in reconnection activity.

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Momentum Transport from Nonlinear Mode Coupling of Magnetic Fluctuations

Cited by 38 publications

References 16 publications

Observation of tearing mode deceleration and locking due to eddy currents induced in a conducting shell

Observation of tearing mode deceleration and locking due to eddy currents induced in a conducting shell

Stochastic magnetic field driven charge transport and zonal flow during magnetic reconnection

Local measurements of tearing mode flows and the magnetohydrodynamic dynamo in the Madison Symmetric Torus reversed-field pinch

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