The effect of isotope mass on the interaction between turbulence and geodesic acoustic mode (GAM) zonal flows has been investigated in HL-2A ohmically heated deuterium (D) and hydrogen (H) plasmas using a double-step Langmuir probe array. The experimental results indicate that the level of GAM zonal flows and the turbulence eddy size together with the eddy tilting angle are all increased in the edge region in D plasmas compared to those in H plasmas under similar discharge parameters involving plasma current, magnetic field and line-averaged density. Evidence shows that in D plasmas, the nonlinear energy transfer is the main cause of the stronger excitation of GAM zonal flows, which extract more energy from ambient turbulence and, consequently, lead to lower turbulent transport and better confinement in D plasmas. The experimental findings may contribute to the understanding of the isotopic physics and associated turbulent transport in tokamak plasmas.
Isotope effect in turbulent transport in high density FT-2 tokamak discharges