Gyrokinetic simulation of the effects of fast ions and impurities on turbulent transport in CFETR hybrid scenario

Abstract This study performs a numerical investigation into the effects of fast ions and impurities in the core region of deuterium–tritium (DT) plasma in the China Fusion Engineering Test Reactor hybrid scenario using the gyrokinetic code NLT. The linear simulations primarily focus on the particle fractions and the density gradients of fast ions and impurities on the linear frequencies of instabilities. The results reveal that tungsten impurities play a negligible impact on the linear frequencies of ion temperature gradient (ITG) instability and trapped electron mode (TEM), whereas argon impurities significantly suppress both ITG and TEM. Fast ions further stabilize ITG instability but destabilize TEM. Electromagnetic effects exhibit a stabilizing influence on both ITG and TEM. Nonlinear simulations demonstrate that the presence of argon impurities and fast ions significantly reduce the ion heat diffusivity, owing to the dilution effects of fast ions and argon impurities. The analysis on the poloidal spectra of perturbed electrostatic potential and DT total energy flux at the saturated stage reveal that ITG instability contributes dominantly to the turbulent transport. The DT total energy flux significantly decreases with a larger positive density gradient of fast ions/impurities. Furthermore, it is revealed that the fast ions suppress the turbulent transport through its dilution effects, while for argon impurities, in addition to the dilution effects, the density gradient effects also play a crucial role, especially under a larger positive density gradient. Moreover, as the density gradient of fast ions/impurities increases, the inward transport of deuterium and tritium particle fluxes are enhanced, and the accumulation of impurities in the core region significantly improves.