  Trapped electron mode turbulence is studied by gyrokinetic simulations with
the GYRO code and an analytical model including the effect of a poloidally
varying electrostatic potential. Its impact on radial transport of high-Z trace
impurities close to the core is thoroughly investigated and the dependence of
the zero-flux impurity density gradient (peaking factor) on local plasma
parameters is presented. Parameters such as ion-to-electron temperature ratio,
electron temperature gradient and main species density gradient mainly affect
the impurity peaking through their impact on mode characteristics. The poloidal
asymmetry, the safety factor and magnetic shear have the strongest effect on
impurity peaking, and it is shown that under certain scenarios where trapped
electron modes are dominant, core accumulation of high-Z impurities can be
avoided. We demonstrate that accounting for the momentum conservation property
of the impurity-impurity collision operator can be important for an accurate
evaluation of the impurity peaking factor.
