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.

Small perturbations and strong impurity exhaust capability associated with the small grassy ELMs render the grassy-ELM regime a suitable candidate for achieving steady-state H-mode operation with a radiative divertor, especially in a metal-wall device, such as the Experimental Advanced Superconducting Tokamak (EAST). As the degradation of pedestal performance with excessive divertor impurity seeding or accumulation tends to be accompanied with significantly increased radiation near the divertor X point, feedback control of the absolute extreme ultraviolet (AXUV) radiation near the X point has been employed to maintain the confinement property in EAST. However, the absolute value of the AXUV radiation at the outer target varies with plasma conditions as during the divertor detachment process. Thus, a new feedback-control scheme has been recently developed and applied to grassy-ELM H-mode plasmas in EAST to achieve stationary partial detachment while maintaining good global energy confinement with H _98,y2 >1. In this scheme, electron temperatures (T _et) measured by divertor Langmuir probes are used to identify the onset of detachment, and then the plasma control system (PCS) switches to the feedback control of one channel of AXUV radiation near the X point, where a steep gradient in the radiation profile is present. The feedback is performed through pulse-width-modulated duty cycle of a piezo valve to seed impurities with mixed gas (50% Ne and 50% D₂) from the outer target plate near the strike point in the upper tungsten monoblock divertor. T _et near the strike point is maintained in the range of 5–8 eV, and peak surface temperature on the outer target plate (T _IR,peak) is suppressed and maintained at ∼180 °C, based on infrared camera measurements. The plasma stored energy maintains nearly constant over the entire feedback-control period. It thus offers a highly promising plasma control scenario suitable for long-pulse high-performance H-mode operation in EAST, which is potentially applicable to future steady-state fusion reactors as an integrated solution for the control of both ELM-induced transient and steady-state divertor heat loads while maintaining good core confinement.

A reproducible stationary high-confinement regime with small “edge-localized modes” (ELMs) has been achieved recently in the Experimental Advanced Superconducting Tokamak, which has a metal wall and low plasma rotation as projected for a fusion reactor. We have uncovered that this small ELM regime is enabled by a wide edge transport barrier (pedestal) with a low density gradient and a high density ratio between the pedestal foot and top. Nonlinear simulations reveal, for the first time, that the underlying mechanism for the observed small ELM crashes is the upper movement of the peeling boundary induced by an initial radially localized collapse in the pedestal, which stops the growth of instabilities and further collapse of the pedestal, thus providing a physics basis for mitigating ELMs in future steady-state fusion reactors.

The Experimental Advanced Superconducting Tokamak (EAST) has recently achieved a variety of H-mode regimes with different edge-localized mode (ELM) dynamics, including type-I ELMs, compound ELMs, which are manifested by the onset of a large spike followed by a sequence of small spikes on D_α emissions, usual type-III ELMs, and very small ELMs. This newly observed very small ELMy H-mode appears to be similar to the type-II ELMy H-mode, with higher repetition frequency (~1 kHz) and lower amplitude than the type-III ELMy H-mode, exhibiting an intermediate confinement level between type-I and type-III ELMy H-modes. The energy loss and divertor power load are systematically characterized for these different ELMy H-modes to provide a physics basis for the next-step high-power long-pulse operations in EAST. Both type-I and compound ELMs exhibit good confinement (H_98(y,2) ~ 1). A significant loss of the plasma stored energy occurs at the onset of type-I ELMs (~8%) and compound ELMs (~5%), while no noticeable change in the plasma stored energy is observed for the small ELMs, including both type-III ELMs and very small ELMs. The peak heat flux on divertor targets for type-I ELMs currently achieved in EAST is about 10 MW m⁻², as determined from the divertor-embedded triple Langmuir probe system with high time resolution. As expected, type-III ELMs lead to much smaller divertor power loads with a peak heat flux of about 2 MW m⁻². Peak power loads for compound ELMs are between those for type-I and type-III ELMs. It is remarkable that the new very small ELMy H-modes exhibit even lower target power deposition than type-III ELMs, with the peak heat flux generally below 1 MW m⁻². These very small ELMs are usually accompanied by broadband fluctuations with frequencies ranging from 20 to 50 kHz, which may promote particle and power exhaust throughout the very small ELMy H-mode regime.

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.

Lower-hybrid waves have been shown to induce a cocurrent change in toroidal rotation of up to 40\,\,km/s in the L-mode plasma core region and 20\,\,km/s in the edge of the EAST tokamak. This modification of toroidal rotation develops on different time scales. For the edge, the time scale is no more than 100~ms, but for the core the time scale is around 1~s. A simple model based on turbulent equipartition and thermoelectric pinch predicts the experimental results.