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Nonlinear mode coupling and sheared flow in a rotating plasma

Uzun Kaymak, İlker Ümit
Guzdar, P. N.
Choi, S.
Clary, M. R.
Ellis, R. F.
Hassam, A. B.
Teodorescu, C.
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. Copyright (C) EPLA, 2009