The effect of sheared E × B flow on the blob dynamics in the scrape-off layer (SOL) of HL-2A tokamak has been studied during the plasma current ramp-up in ohmically heated deuterium plasmas by the combination of poloidal and radial Langmuir probe arrays. The experimental results indicate that the SOL sheared E × B flow is substantially enhanced as the plasma current exceeds a certain value and the strong sheared E × B flow has the ability to slow the blob radial motion via stretching its poloidal correlation length. The locally accumulated blobs are suggested to be responsible for the increase of plasma density just outside the Last Closed Flux Surface (LCFS) observed in this experiment. The results presented here reveal the significant role played by the strong sheared E × B flow on the blob dynamics, which provides a potential method to control the SOL width by modifying the sheared E × B flow in future tokamak plasmas.

The effect of impurity ions on the coupling between geodesic acoustic mode (GAM) zonal flows and local turbulent transport has been studied using a Langmuir probe array in HL-2A ohmically-heated deuterium plasmas. The experimental results illustrate that both frequency and amplitude level of the GAM zonal flow significantly reduce with the increase of carbon ions concentration, which is qualitatively consistent with the theoretical prediction [B. Xie et al. Plasma Phys. Controlled Fusion 60 025015 (2018)], meanwhile the less energy is transferred from turbulence to GAM zonal flows due to the reduction in tilting and stretching of turbulent vortex. Consequently, the impurity ions stir the enhancement of turbulence and turbulent transport owing to the reduced GAM zonal flow as demonstrated in the experiment. These experimental results presented here therefore reveal the dual roles played by impurity ions on the dynamics of GAM zonal flows.

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.