Density and magnetic fluctuations at JET: experimental observation and numerical characterization

Density and magnetic fluctuations have been experimentally observed on JET in the inter ELM phases in low ?e discharges through a correlation reflectometer and a high resolution magnetic coil array. They have been characterized in terms of typical frequency range (60-80 kHz), radial localization (pedestal top), correlation with the relevant kinetic quantities and, for magnetic measurements, in terms of local wavenumber (0.01< ky?i <0.1) [1]. The nature of these fluctuations is discussed along with linear gyrokinetic simulations performed through the GENE code [2]. Ion temperature gradient (ITG) modes are the dominant instabilities in the frequency range of interest. In terms of amplitude and radial envelope ITG modes are consistent with the experimental density fluctuation measurements. Micro-tearing modes, unstable at the lowest wavenumbers, could instead explain magnetic fluctuation measurements through a non-linear process which will be preliminarily addressed.