Resonant drive and nonlinear suppression of gradient-driven instabilities via interaction with shear Alfvén waves

D. W. Auerbach; T. A. Carter; S. Vincena; P. Popovich

doi:10.1063/1.3574506

Resonant drive and nonlinear suppression of gradient-driven instabilities via interaction with shear Alfvén waves

D. W. Auerbach, T. A. Carter, S. Vincena, P. Popovich

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7 Scopus citations

Abstract

The nonlinear interaction of shear Alfvén waves and gradient-driven instabilities on pressure gradients in the Large Plasma Device (LAPD) [Gekelman, Rev. Sci. Instrum. 62, 2875 (1991)] at UCLA is explored. Nonlinear response at the beat frequency between two shear Alfvén waves is shown to resonantly drive unstable modes as well as otherwise damped modes. Resonantly driving the damped modes is shown to suppress the originally unstable mode, leaving only the beat-driven response with an overall reduction in fluctuation amplitude. A threshold is observed in the suppression behavior, requiring that the driven damped mode power be of order 10 of the power in the saturated unstable mode. The interaction is also observed to be dependent on the parallel wavenumber of the driven beat wave; efficient coupling and suppression is only observed for co-propagating beat waves with small parallel wavenumber, consistent with the parallel wavenumber of the gradient-driven modes.

Original language	English
Article number	055708
Journal	Physics of Plasmas
Volume	18
Issue number	5
DOIs	https://doi.org/10.1063/1.3574506
State	Published - May 2011
Externally published	Yes

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title = "Resonant drive and nonlinear suppression of gradient-driven instabilities via interaction with shear Alfv{\'e}n waves",

abstract = "The nonlinear interaction of shear Alfv{\'e}n waves and gradient-driven instabilities on pressure gradients in the Large Plasma Device (LAPD) [Gekelman, Rev. Sci. Instrum. 62, 2875 (1991)] at UCLA is explored. Nonlinear response at the beat frequency between two shear Alfv{\'e}n waves is shown to resonantly drive unstable modes as well as otherwise damped modes. Resonantly driving the damped modes is shown to suppress the originally unstable mode, leaving only the beat-driven response with an overall reduction in fluctuation amplitude. A threshold is observed in the suppression behavior, requiring that the driven damped mode power be of order 10 of the power in the saturated unstable mode. The interaction is also observed to be dependent on the parallel wavenumber of the driven beat wave; efficient coupling and suppression is only observed for co-propagating beat waves with small parallel wavenumber, consistent with the parallel wavenumber of the gradient-driven modes.",

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AU - Auerbach, D. W.

AU - Carter, T. A.

AU - Vincena, S.

AU - Popovich, P.

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N2 - The nonlinear interaction of shear Alfvén waves and gradient-driven instabilities on pressure gradients in the Large Plasma Device (LAPD) [Gekelman, Rev. Sci. Instrum. 62, 2875 (1991)] at UCLA is explored. Nonlinear response at the beat frequency between two shear Alfvén waves is shown to resonantly drive unstable modes as well as otherwise damped modes. Resonantly driving the damped modes is shown to suppress the originally unstable mode, leaving only the beat-driven response with an overall reduction in fluctuation amplitude. A threshold is observed in the suppression behavior, requiring that the driven damped mode power be of order 10 of the power in the saturated unstable mode. The interaction is also observed to be dependent on the parallel wavenumber of the driven beat wave; efficient coupling and suppression is only observed for co-propagating beat waves with small parallel wavenumber, consistent with the parallel wavenumber of the gradient-driven modes.

AB - The nonlinear interaction of shear Alfvén waves and gradient-driven instabilities on pressure gradients in the Large Plasma Device (LAPD) [Gekelman, Rev. Sci. Instrum. 62, 2875 (1991)] at UCLA is explored. Nonlinear response at the beat frequency between two shear Alfvén waves is shown to resonantly drive unstable modes as well as otherwise damped modes. Resonantly driving the damped modes is shown to suppress the originally unstable mode, leaving only the beat-driven response with an overall reduction in fluctuation amplitude. A threshold is observed in the suppression behavior, requiring that the driven damped mode power be of order 10 of the power in the saturated unstable mode. The interaction is also observed to be dependent on the parallel wavenumber of the driven beat wave; efficient coupling and suppression is only observed for co-propagating beat waves with small parallel wavenumber, consistent with the parallel wavenumber of the gradient-driven modes.

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Resonant drive and nonlinear suppression of gradient-driven instabilities via interaction with shear Alfvén waves

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