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Open AccessFeature PaperArticle

Amplitude Modulation And Nonlinear Self-Interactions of the Geodesic Acoustic Mode at the Edge of MAST

Physics Department, University of Warwick, Coventry CV4 7AL, UK
EURATOM/CCFE Fusion Association, Culham Science Centre, Abingdon OX14 3DB, UK
Author to whom correspondence should be addressed.
Plasma 2019, 2(2), 168-178;
Received: 1 April 2019 / Revised: 23 April 2019 / Accepted: 1 May 2019 / Published: 8 May 2019
(This article belongs to the Special Issue Magnetic Confinement Fusion)
We studied the amplitude modulation of the radial electric field constructed from the Langmuir probe plasma potential measurements at the edge of the mega-ampere spherical tokamak (MAST). The Empirical Mode Decomposition (EMD) technique was applied, which allowed us to extract fluctuations on temporal scales of plasma turbulence, the Geodesic Acoustic Mode (GAM), and those associated with the residual poloidal flows. This decomposition preserved the nonlinear character of the signal. Hilbert transform (HT) was then used to obtain the amplitude modulation envelope of fluctuations associated with turbulence and with the GAM. We found significant spectral coherence at frequencies between 1–5 kHz, in the turbulence and the GAM envelopes and for the signal representing the low frequency zonal flows (LFZFs). We present the evidence of local and nonlocal, in frequency space, three wave interactions leading to coupling between the GAM and the low frequency (LF) part of the spectrum. View Full-Text
Keywords: fusion plasma; radial electric field; temporal intermittency fusion plasma; radial electric field; temporal intermittency
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Hnat, B.; Walkden, N.; The MAST Team. Amplitude Modulation And Nonlinear Self-Interactions of the Geodesic Acoustic Mode at the Edge of MAST. Plasma 2019, 2, 168-178.

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