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The analysis of magnetic fluctuations in the JET and TCA tokamaks is presented. Observations on the spatial structure of turbulent magnetic activity in JET confirm its strong correlation with the degradation of energy confinement. Two types of turbulent magnetic fluctuations are present simultaneously. The first type, dominant at low frequency and correlated with the visible light fluctuations, presents a w/k= constant dispersion relationship. The second one is stationary and is dominant in the higher frequency range (10 to 20 kHz). In TCA and JET, the level of magnetic fluctuations is observed to increase when the energy confinement time decreases. The analysis of a magnetic perturbation - the gong - appearing at the time of the sawtooth instability growth shows that the gong is in fact the magnetic signature of the instability itself. It provides a new means to analyse poloidally and toroidally the sawtooth instability. A toroidal plasma rotation is deduced from analysis of the coherent magnetic fluctuations and the radial ambipolar electric field is estimated. A new type of magnetic oscillation is shown to be present during the stable phase of a locked-mode. This is interpreted as a destabilised interchange mode. Finally the analysis of coherent magnetic fluctuations leads to the deduction of a toroidal plasma rotation and estimation of the radial ambipolar electric field. It has been possible to show the existence of a new type of magnetic oscillation which is present during the stable phase of a locked-mode.

Additional information

Authors: DUPERREX P A, Centre de Recherches en Physique des Plasmas, École Polytechnique Fédérale de Lausanne (CH)
Bibliographic Reference: Report: LRP 343/88 EN (1988)
Availability: Available from Confédération Suisse, Centre de Recherches en Physique des Plasmas, Ecole Polytechnique Fédérale de Lausanne, 21 avenue des Bains, 1007 Lausanne (CH)
Record Number: 198910607 / Last updated on: 1994-12-01
Original language: en
Available languages: en
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