Main Ion Isotope dependence of impurity transport in ion and electron-heating dominated H-mode plasmas in the DIII-D tokamak

The impurity confinement time τ_imp is up to 3x shorter in hydrogen (H) plasmas than in dimensionally similar deuterium (D) plasmas. The transport of calcium is investigated with the laser blow-off system in ELM-y H-mode discharges. Adding ECH to NBI heated D discharge reduces τ_imp 3x while τ_imp remains unaffected by ECH in H plasmas. The lack of τ_imp variation in H is a consequence of the 10x faster impurity diffusion compared to an NBI-heated D reference, which only slightly increases with ECH. The normalized impurity density gradient R/L_n is nearly identical for the H and D plasmas, rising from -2 in NBI heated plasmas to 2 in NBI+ECH heated plasmas. Turbulent transport is modeled by the quasilinear CGYRO model, which correctly reproduces the increase in impurity diffusion caused by a change of heating mix. However, the diffusion in H compared to the D case increases only by a factor 2-3, while in the experiment by a factor of 10. A sensitivity scan by CGYRO indicates impurity transport is mainly affected by indirect effects associated with the isotope change, such as profile gradients, electron-ion heat exchange, and beta stabilization but negligible direct effects of isotope.