Validation of nonlinear gyrokinetic modeling of isotope-dependent impurity transport in the DIII-D tokamak

Experimental investigation of impurity transport with laser blow-off in DIII-D revealed a difference in calcium transport between deuterium (D) and dimensionally similar hydrogen (H) plasma. Impurity confinement time in D is up to 3x longer and with a stronger dependence on ECH power than in H. Only a weak isotope dependence of mid-radius impurity diffusion was observed in ECH heated plasmas. In contrast, the diffusion is an order of magnitude lower in D than in H in the NBI-only heated case. The ratio between mid-radius impurity convection and diffusion remained unchanged between the isotopes. The experimental observations are compared with local non-linear gyrokinetic modeling using the CGYRO code. The heat flux matched CGYRO simulations reproduce the observed increase of impurity diffusion and pinch with additional ECH power for both isotopes. However, the magnitude of diffusion in NBI heated H plasma is underestimated by a factor of four. Parameters sensitivity scan performed by CGYRO indicates that the variation in transport coefficients is a consequence of indirect changes between H and D plasma, such as in the profiles gradients, T_e/T_i ratio, and beta stabilization, rather than a direct influence of the isotope mass.