Specific turbulence associated with sawtooth relaxations in TFR plasmas

The specific turbulence during the sawtooth relaxation which superimposes the quasi-stationary (QS) turbulence, is investigated. Experimentally it corresponds to burts of fluctuations observed on the high frequency side of the QS spectrum. A CO2 coherent scattering diagnostic is used to perform the experiments. The scattering volume consists on a vertical chord which is radially scanned. The experiments, performed on TFR tokamak, concern k = 5 or 7/cm. The analysis of the temporal amplitude variation allows to define three stages in the turbulent process. Each stage typically lasts 20μs. The azimutal and the radial localizations are studied. It is concluded that the turbulence is azimutally localized on the cold side. Concerning the numerical model, a spatial level model decaying in both the r and θ directions (with gaussian profiles), is adapted. The azimutal direction in which the heat flux appears is defined by means of the soft X-rays signals. It is shown that the lifetime of the cell of turbulence (localized in the interior of the q=1 surface with an azimutal full width extension of about 120 degrees) coincides with the collapse of the sawtooth. These observations are in agreement with the so called ''magnetodrift'' turbulence in the sawtooth disruption model