Description
The value of gyrokinetic simulation and modelling of tokamaks lies in providing insights for the development of future laboratory machines and reactors, such as ITER, DEMO and fusion plants. Gyrokinetic simulations already indicate that in future, larger tokamaks, the anomalous transport level will follow a gyro-Bohm scaling, in contrast to a Bohm scaling observed in smaller, past and present-day tokamaks. Meanwhile, a flux-driven full-f simulation has not observed a transition to gyro-Bohm scaling from a system size scan due to prevalent large scale non-local avalanches.
The most efficient way to achieve burning plasmas in future tokamaks and fusion plants is to utilize hydrogen isotopes deuterium (D) and tritium (T), leveraging their favorable fusion cross sections. Predictions of isotope effects for future tokamaks heavily rely on empirical scaling laws, such as L-mode confinement scaling ITER89-P and the H-mode confinement scaling ITER-IPB(y), along with ITPA activities.
Recently, gyrokinetic simulations have quantitatively reproduced the empirical scaling law[L. Qi P. R. Research 2024]. This quantitative agreement provides a solid basis for exploring isotope effects in forthcoming tokamaks. In this work[L. Qi NF 2025], we present a reversal in the isotopic dependence of energy confinement in the tokamak plasma core from past to future tokamaks. This finding offers critical insights for the design of future tokamaks, such as ITER, DEMO and fusion plants, particularly those with larger sizes or stronger magnetic fields.
On the other hand, future tokamaks, will likely operate in H-mode. Predicting the role of isotope mass in energy confinement for these H-mode scenarios remains a critical challenge. While the plasma core contains most of the plasma energy, the pedestal, characterized by a sharp transport barrier, plays a crucial role in overall confinement. Understanding isotope effects in the pedestal region is a critical and challenging issue. In this work[L. Qi paper in preparation], we will also extend our study from the core, and report on the trend of isotopic dependence in H-mode pedestal confinement as system size increases to that of future tokamaks.