Density fluctuations associated with the sawtooth internal disruption
Résumé
Fluctuations specially related to the sawtooth internal disruption has been observed on TFR tokamak plasmas by analyzing the fluctuations density with CO2 laser light scattering. The time localization is clearly connected with the successive phases of the relaxation process. Some specific fluctuations appear in relation to the kink motion, but te main burst corresponds to the collapse phase. We concentrate our study on this strong burst and show first its frequency and wave number spectral properties and the corresponding pseudo dispersion relation. The fluctuations are spatially localized. They are within the interior of the q = 1 surface and extend approximately 120° azimuthally. Taking into account the twisting of the central plasma during the turbulent kink phase, this location agrees with the azimuthal position of the ≪ sooner and faster ≫ outgoing heat flux. The power level of these fluctuations is two orders of magnitude larger than the local quasi-stationary turbulence. These observations are in fair agreement with the predictions of the sawtooth disruption model previously proposed by Andreoletti. The observed specific fluctuations show several similarities with the so-called ≪ magnétodrift turbulence ≫ described in the model.
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