The Study of Multi-Z Impurity Transport in DIII-D ITER Similar Shape Discharges*

The diffusion and convection of impurities arising from neoclassical and turbulent transport mechanisms has been studied in a set of DIII-D discharges operated with the ITER shape, RMP ELM suppression, and approximately equal ion and electron heat loss (Qi~Qe).  Neoclassical and nonlinear, flux-matched (Qi, Qe, Ge) gyrokinetic simulations (NEO and CGYRO) were performed from the plasma axis to near the pedestal top (rho = 0.0 – 0.8) to assess the relative impact of collisions and turbulence on the transport of 7 impurities (He, Li, C, F, Al, Ca, and W).  Inside of rho = 0.45 simulation predicts a negative correlation of diffusion with Z, in contrast to a strong positive correlation found outside of this region.  Linear simulations suggest these trends may be linked to the dominant local instabilities (ITG/TEM) but the physical origin is the subject of ongoing investigations.  We will present a summary of the experiments, gyrokinetic and neoclassical simulations, and comparisons with experimentally determined impurity transport in the target discharges.