Validation of gyrokinetic impurity transport models and experimental measurement of rotodiffusion in DIII-D tokamak

Validation of gyrokinetic particle transport models is crucial for predictions of low-Z impurity profiles in fusion reactors and helps to advance research of high-Z impurities which cannot be diagnosed with sufficient accuracy. The peaking of carbon density is investigated in a database of 143 H-mode discharges. Experimental $R/L_{n_C}$ values are contrasted with quasilinear gyrokinetic modeling by CGYRO. Linear multi regression analysis identified $\omega_r$ and parallel compressibility $k_{||}^2=(\hat{s}/qR)^2$ as the major parameters, explaining 93\% of non-random variance in the measured $R/L_{n_C}$. In ITG cases, CGYRO reproduced 95\% of dependence on $\omega_r$, however only 36\% of variation connected to $k_{||}^2$. Such discrepancy points to a significantly under-predicted parallel compressibility drift in the model. The remaining discrepancy indicates a too high sum of inward curvature drift together with outward thermo-diffusion. The rotodiffusion contribution in the rotation scans was near zero. Finally, we have compared the database with nonlinear ion scale CGYRO runs, and gyrofluid TGLF runs. While quasilinear runs reproduce $ R/L_{n_C}$ from nonlinear runs remarkable well, a significant discrepancy is found in TGLF thermodiffusion.