Gyrokinetic simulations of ion temperature gradient instability in deuterium-tritium plasma in the CFETR hybrid scenario

The linear instabilities and nonlinear transport driven by the ion temperature gradient (ITG) instability are numerically investigated in deuterium-tritium plasma in the CFETR hybrid scenario by using the NLT code. In both linear and nonlinear simulations, effects of the tritium fraction epsilon(T) and the temperature ratio of deuterium and tritium tau(DT) = T-D/T-T are studied, with T-D and T-T being the temperature of deuterium and tritium, respectively. Results from linear simulations illustrate that the ITG instability can be well stabilized as epsilon(T) increases. When epsilon(T) = 0.5, the maximum growth rate occurs at around tau(DT) = 1.5. During the nonlinear simulations, the anomalous particle and energy flux in deuterium-tritium plasma are analyzed. For tau(DT) = 1.0, it is found that the tritium (deuterium) particle flux is inward (outward) and the largest inward tritium particle flux appears at epsilon(T) = 0.5. The total ion energy flux is found to be insensitive to epsilon(T). In the case with epsilon(T) = 0.5, as tau(DT) decreases from 3.0 to 0.5, the particle flux for tritium (deuterium) changes from the outward (inward) direction to the inward (outward) direction. The quasilinear analysis clarifies that the particle flux driven by the temperature gradient is the key part in determining the direction of the particle flux. Besides, the largest and the smallest energy flux appear at around tau(DT) = 1.5 and 0.5, respectively. It is indicated that better energy confinement and better particle confinement for tritium could be realized by choosing smaller tau(DT) (or higher T-T). (c) 2023 Author(s). All article content, except where otherwise noted, is licensed under a Creative Commons Attribution (CC BY) license (http://creativecommons.org/licenses/by/4.0/).