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.