Role of isotopes in microturbulence from linear to saturated Ohmic confinement regimes*

The first principle gyrokinetic numerical experiments investigating the isotopic dependence of energy confinement achieve a quantitative agreement with experimental empirical scalings, particularly in Ohmic and L-mode tokamak plasmas. Mitigation of turbulence radial electric field intensity  and associated poloidal  fluctuating velocity with the radial correlation length  strongly deviating from the gyro-Bohm scaling is identified as the principal mechanism behind the isotope effects. Three primary contributors are classified, the deviation from gyro-Bohm scaling, zonal flow and trapped electron turbulence stabilization. Zonal flow enhances isotope effects primarily through reinforcing the inverse dependence of turbulence decorrelation rate on isotope mass with , which markedly differs from the characteristic linear frequency. The findings offer new insights into isotope effects, providing critical implications for energy confinement optimization in tokamak plasmas.