Validation of gyro-kinetic predictions of TEM-driven electron transport against JET experiments

A main drive for electron heat transport in tokamaks is the Trapped Electron Mode (TEM) instability. This work explores the parametric dependencies of TEM threshold and stiffness both experimentally in JET C-wall L-mode plasmas and theoretically by linear and non-linear gyro-kinetic simulations using GKW[1]. Stabilizing effects of the magnetic shear s and collisionality are foreseen by theory and evidenced also in the JET experiments, whilst a weaker destabilizing effect of R/Ln could not be isolated in experiments due to strong coupling between R/Ln and s. No effects of q and Te/Ti were found. Good agreement between the experimental and theory predicted stiffness level has been found. An increase of R/LTi in presence of significant ion heating results in a reduction of R/LTe, in part due to increased electron stiffness and in part to additional electron transport via the ITG channel.!