Gyrokinetic modeling of impurities during the H-mode pedestal inter-ELM buildup

We study profiles from the DIII-D H-mode inter-ELM buildup phase that show hollow Carbon and electron profiles. These experimental results are interesting because inward impurity flux may be partially responsible for the electron density buildup. We have carried out linear gyrokinetic simulations using the GENE code in the flux-tube limit and study the pedestal top in the range of ??_tor=0.8-0.95 where closed-flux-surface calculations are valid. We find ITG and TEM modes most unstable in the ion-scale range and ETG most unstable in the electron scale range. Quasilinear calculations indicate that the anomalous particle transport is dominated by ITG or ion-scale modes with phase velocity in the ion diamagnetic direction. The quasilinear calculations show negative particle fluxes for both electrons and Carbon. These results are being compared to neoclassical calculations using the NEO code. We use these linear and quasilinear calculations as a scoping tool for nonlinear GEM simulations. Understanding the impurity transport, especially if impurity fluxes are inward, is critical for future fusion reactors where high-Z impurities may not fully ionize in the core leading to significant radiative power loss.