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The internal transport barrier (ITB) has been obtained in ELMy H-mode plasmas by neutron beam injection and lower hybrid wave heating on the Experimental Advanced Superconducting Tokamak (EAST). The ITB structure has been observed in profiles of ion temperature, electron temperature, and electron density within ρ < 0.5. It was also observed that the ITB formation is stepwise. Due to the ITB formation, the confinement quality H 98y2 increases from 1 to 1.1 and the normalized beta, β N, increases from 1.5 to near 2. The fishbone activity observed during the ITB phase suggests the central safety factor q(0) ~ 1. Transport coefficients are calculated by particle balance and power balance analysis, showing an obvious reduction after the ITB formation.

A coherent mode (CM) in the edge pedestal region has been observed on different fluctuation quantities, including density fluctuation, electron temperature fluctuation and magnetic fluctuation in H mode plasma on the Experimental Advanced Superconducting Tokamak (EAST) tokamak. Measurements at different poloidal positions show that the local poloidal wavenumber is smallest at the outboard midplane and will increase with poloidal angle. This poloidal asymmetry is consistent with the flute-like assumption (i.e. k// ~ 0) from which the toroidal mode number of the mode has been estimated as between 12 and 17. It was further found that the density fluctuation amplitude of the CM also demonstrated poloidal asymmetry. The appearance of a CM can clearly decrease or even stop the increase in the edge density, while the disappearance of a CM will lead to an increase in the pedestal density and density gradient. Statistical analysis showed there was a trend that as the CM mode amplitude increased, the rate of increase of the edge density decreased and the particle flux (Γdiv) onto the divertor plate increased. The CM sometimes showed burst behavior, and these bursts led bursts on Γdiv with a time of about 230 μs, which is close to the time for particle flow from the outer midplane to the divertor targets along the scrape-off layer magnetic field line. This evidence showed that the CM had an effect on the outward transport of particles.

The density roll-over dependence on H-mode power threshold is observed on EAST for the first time. In campaign 2014 and 2015 shots with a toroidal field of 2.25 T have observed roll-over dependence with lower hybrid wave as the only auxiliary heating method, while shots with a toroidal field of 1.79 T and 1.9 T exhibit linear dependence consistent with scaling law. The density of minimum power for accessing H-mode on EAST has different plasma current values of 400 kA and 500 kA, and is better described in the normalized Greenwald fraction at . The absence of in 1.7 T and 1.8 T may be attributed to the positive dependence with toroidal field. Besides, correlation analysis of H-mode power threshold and divertor geometry in scanning X-point is summarized and compared. Outer leg length (distance from X-point to outer strike point) has the highest correlation coefficient with H-mode power threshold, which explains the data scattering within the same plasma parameters. A new equation of scaling law is proposed: Neutral particles are believed to be the hidden factor in different divertor geometry, and play a negative role in L–H transition via charge exchange damping.

Edge localized mode (ELM)-filament statistical characteristics and intermittent convective transport are studied during ELM mitigation (10–30 ms) induced by supersonic molecular beam injection (SMBI) on the HL-2A tokamak. Langmuir probe data show that the burst rate of large amplitude filaments (δne > 4σ) decreases by 30–50% and their radial velocity decreases by 40–60%, which is an indication of an amplitude reduction. A decrease of long-range correlation along the magnetic flux surface is observed after SMBI, indicating a role of electron–ion collisionality on the filament parallel current in the ELM mitigation time. The transient particle and heat fluxes decrease about 40–50% and 50–60%, respectively. These observations indicate that SMBI might be an effective method to suppress the intermittent convective transport.

Measurements with a toroidally and poloidally displaced three-dimensional set of Langmuir probe arrays have revealed details of turbulence, geodesic acoustic modes (GAMs), zonal flows and their interactions in the edge region of HL-2A tokamak plasmas. The coexistence of intensive low frequency zonal flows (LFZFs) of f < 4 kHz and the GAMs of 7 kHz < fGAM < 20 kHz has been unambiguously demonstrated. The poloidal and toroidal symmetries of the flows, including the GAMs, are verified experimentally. In particular, the coherency of the flows over a large toroidal scale of 2100 mm at a magnetic flux surface is emphasized. The LFZF packets are shown to propagate outward and inward as equally likely events, whereas the predominantly outward propagation of the GAM packets is analyzed. The nonlinear three-wave coupling of the flows with ambient turbulence is shown with a bicoherency analysis and an envelope modulation of the latter by the former. The intensity of the LFZFs is observed to increase and decrease with increases in ECRH power (~300–700 kW) and safety factor q ~ (3.5–6.2), respectively, whereas the intensity of the GAMs increases with increases in both ECRH power and q.

The spectral characteristics of zonal flows, including both the geodesic acoustic mode (GAM) and the zero/low frequency zonal flow (LFZF), are investigated by applying the two-point correlation technique and bispectral analysis to the floating potential fluctuations measured by several Langmuir probe arrays on the HT-7 tokamak. The three-dimensional wavenumber and frequency spectra for the two modes have been estimated. The radial wavenumber spectra show that the LFZF packages propagate both outward and inward while the GAM packages propagate outward mostly. Nonlinear couplings betweeen zonal flows and ambient turbulence are observed in the biphase while the bicoherence at the GAM frequency is much larger than that at the LFZF frequency. A kind of mode with frequencies higher than that of GAM, which may also be generated from the ambient turbulence in a similar way as the zonal flows, is reported.