Identifying the role of non-adiabatic passing electrons in ITG/TEM microturbulence by comparing fully kinetic and hybrid electron simulations
The response of passing electrons in Ion Temperature Gradient (ITG) and Trapped Electron Mode (TEM) microinstability regimes is investigated in tokamak geometry making use of the flux-tube version of the gyrokinetic code GENE [Jenko et al. 2000 Phys. Plasmas 7 1904]. Results are obtained with two different electron models: 1) fully kinetic, and 2) hybrid, in which passing particles are forced to respond adiabatically while trapped are handled kinetically. Comparing linear eigenmodes obtained with these two models enables to systematically isolate radially fine structures located at corresponding MRS's, clearly resulting from the non-adiabatic passing electron response. The analysis of preliminary non-linear simulations in the ITG regime shows that these fine structures on the non-axisymmetric modes survive in the turbulent phase. Furthermore, through non-linear coupling to axisymmetric modes, they induce modulations in the effective density and ion/electron temperature profiles: flattening at low order MRS's and steepening in between, as was already observed in Ref. [Waltz et al., 2006 Phys. Plasmas 13 052301].