Mastering nuclear fusion, which is an abundant, safe, and environmentally competitive energy, is a great challenge for humanity. Tokamak represents one of the most promising paths toward controlled fusion. Obtaining a high-performance, steady-state, and long-pulse plasma regime remains a critical issue. Recently, a big breakthrough in steady-state operation was made on the Experimental Advanced Superconducting Tokamak (EAST). A steady-state plasma with a world-record pulse length of 1056 s was obtained, where the density and the divertor peak heat flux were well controlled, with no core impurity accumulation, and a new high-confinement and self-organizing regime (Super I-mode = I-mode + e-ITB) was discovered and demonstrated. These achievements contribute to the integration of fusion plasma technology and physics, which is essential to operate next-step devices.

Since the last IAEA-Fusion Energy Conference, the Experimental Advanced Superconducting Tokamak (EAST) research program has been, in support of ITER and CFETR, focused on development in terms of the long-pulse steady-state (fully noninductive) high beta H-mode scenario with active controls of the stationary and transient divertor heat and particle fluxes. The operational domain of the steady-state H-mode plasma scenario has been significantly extended with ITER-like tungsten mono-block divertor, plasma control and heating schemes. EAST has achieved several important milestones in the development of high β _p H-mode scenario and its key physics and technologies. A 60 s-scale long-pulse steady-state high β _p H-mode discharge with the major normalized plasma parameters similar to the designed performance of the CFETR 1 GW fusion power operation scenario has been successfully established and sustained by pure RF heating and current drive. Several feedback control schemes have been developed for a sustained detachment with good core confinement. This includes control of the total radiation power, target electron temperature, and particle flux measured using divertor Langmuir probes or a combination of the control of target electron temperature and AXUV radiation near the X point. The detachment feedback control schemes have been integrated with small-ELM regimes and high β _p scenario via neon seeding, enabling a core and edge compatible integrated high-beta scenario applicable to long-pulse operations. ELM suppression has been achieved using various methods, including resonant magnetic perturbations and impurity seeding. Full suppression of ELMs by using n = 4 RMPs has been demonstrated for ITER for the first time in low input torque plasmas in EAST. EAST has been operated with helium to support the ITER research requirements for the first time. For a long-pulse, high bootstrap current fraction operation, a new lower tungsten divertor with active water-cooling has been installed, along with improvements in the heating and current drive capability.

Extreme ultraviolet (EUV) spectra emitted from iron and copper ions in a range of 8–500 Å and molybdenum ions in a range of 8–400 Å were measured in Experimental Advanced Superconducting Tokamak (EAST) discharges accompanied with spontaneous sputtering events, by which metallic impurity influxes are suddenly increased in the discharge. Several spectral lines from L-, M-, and N-shell partially ionized ions have been successfully observed with two EUV spectrometers named EUV_Short and EUV_Long working in wavelength ranges of 8–130 Å and 20–500 Å, respectively. The wavelength position is accurately calibrated in-situ based on several well-known spectra of low-Z impurity ions. The line identification is carefully performed based on the National Institute of Standards Technology (NIST) database and previously published experimental data. As a result, it is found that B-, Be-, and Li-like iron and copper spectra Al-, Mg-, and Na-like molybdenum spectra appear in discharges with high central electron temperature (>1.8 keV). The highest ionization stages identified here are Li-like iron and copper and Na-like molybdenum, e.g. Fe XXIV at 192.028 Å (1s ² 2p ² P _3/2 → 1s ² 2s ² S _1/2 ), Cu XXVII at 153.513 Å (1s ² 2p ² P _3/2 → 1s ² 2s ² S _1/2 ) and Mo XXXII at 127.868 Å (2p ⁶ 3p ² P _3/2 → 2p ⁶ 3s ² S _1/2 ). Two unresolved transition arrays of molybdenum ions (Mo-UTAs) appear at wavelength ranges of 15–30 Å and 65–95 Å, and are preliminarily identified as Mo XX-Mo XXXII and Mo XVII-Mo XXXII, respectively. In addition, six spectral lines are newly found by comparing a time evolution of the line intensity from impurity ions in different ionization stages, i.e. Fe XVIII at 17.60 ± 0.02 Å, Cu XXI at 13.15 ± 0.02 Å, Cu XVIII at 260.32 ± 0.07 Å, Cu XVIII at 261.00 ± 0.06 Å, Mo XXVIII at 85.30 ± 0.03 Å and Mo XXIX at 89.59 ± 0.03 Å. The wavelengths of EUV spectra identified in this work are summarized in tables with transitions for each impurity species.

A quasi-coherent mode (QCM) was measured by the tangential CO₂ laser collective scattering diagnostic at high plasma electron density during both enhanced D_α/small edge-localized mode (ELM) and ELM-free H mode phases in Experimental Advanced Superconducting Tokamak (EAST). Experimental results from only local oscillator CO₂ laser scattering prove that the QCM is measured by the scattering diagnostic in the far-forward mode. The driven QCM density fluctuation ($k_{\perp }<3$ cm⁻¹) and magnetic fluctuation suggest that the QCM is an electromagnetic mode. The typical frequency of the QCM is f ≈ 26.5 kHz. A combination analysis of scattering signals and Mirnov signals suggests that the QCM has toroidal mode number n ≈ 17 and rotates along with the electron diamagnetic drift velocity direction in the lab frame. The analysis of Mirnov and reflectometer signals supports that the QCM locates in the edge pedestal region. The QCM power has been found to be related to both the D_α signal and the pedestal density gradient. A comparison of the EAST QCM and C-Mod quasi-coherent mode has been given in detail.

A recent EAST experiment has successfully demonstrated long pulse steady-state high plasma performance scenario and core-edge integration since the last IAEA in 2018. A discharge with a duration over 60 s with β _P ∼ 2.0, β _N ∼ 1.6, H_98y2 ∼ 1.3 and an internal transport barrier on the electron temperature channel is obtained with multi-RF power heating and current drive. A higher β _N (β _N ∼ 1.8, β _p ∼ 2.0, H_98y2 ∼ 1.3, n _e/n _GW ∼ 0.75) with a duration of 20 s is achieved by using the modulated neutral beam and multi-RF power, where several normalized parameters are close or even higher than the phase III 1 GW scenario of CFETR steady-state. High-Z impurity accumulation in the plasma core is well controlled in a low level by using the on-axis ECH. Modeling shows that the strong diffusion of TEM turbulence in the central region prevents tungsten impurity from accumulating. More recently, EAST has demonstrated compatible core-edge integration discharges in the high β _p scenario: high confinement H_98y2 > 1.2 with high β _P ∼ 2.5/β _N ∼ 2.0 and f _bs ∼ 50% is sustained with reduced divertor heat flux at high density n _e/n _GW ∼ 0.7 and moderate q ₉₅ ∼ 6.7. By combining active impurity seeding through radiative divertor feedback control and strike point splitting induced by resonant perturbation coil, the peak heat flux is reduced by 20–30% on the ITER-like tungsten divertor, here a mixture of 50% neon and 50% D₂ is applied.