Nonlinear mode coupling and sheared flow in a rotating plasmaİ. Ü. Uzun-Kaymak, P. N. Guzdar, S. Choi, M. R. Clary, R. F. Ellis, A. B. Hassam and C. Teodorescu
Institute for Research in Electronics and Applied Physics, University of Maryland - College Park, MD 20742, USA
received 3 September 2008; accepted in final form 23 November 2008; published January 2009
published online 7 January 2009
Shear flow is expected to stabilize the broad spectrum of interchange modes in rotating plasmas. However, residual fluctuations may still persist. To investigate the presence of such fluctuations, sixteen magnetic pickup coils equally spaced on a crown have been mounted inside the vacuum vessel, at the edge of a rotating plasma in mirror configuration. A comprehensive analysis of the magnetic fluctuations shows that very low spatial mode numbers survive under the imposed shear flow. Nevertheless, temporal Fourier analysis reveals a broadband frequency spectrum. Clear evidence of nonlinear mode coupling is obtained using higher-order spectral analysis, namely the bispectrum and the bicoherence. Two-dimensional simulations of magnetohydrodynamic equations with gravity and imposed shear flow quantitatively model the spatio-temporal characteristics of the observed magnetic fluctuations.
52.35.Ra - Plasma turbulence.
52.35.Mw - Nonlinear phenomena: waves, wave propagation, and other interactions (including parametric effects, mode coupling, ponderomotive effects, etc.).
52.35.Py - Macroinstabilities (hydromagnetic, e.g., kink, fire-hose, mirror, ballooning, tearing, trapped-particle, flute, Rayleigh-Taylor, etc.).
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