A team at the Institute of Plasma Physics, Chinese Academy of Sciences (ASIPP) has achieved a long-pulse, high-confinement plasma discharge lasting 1,056 seconds in the Experimental Advanced Superconducting Tokamak (EAST). The result, detailed in a peer-reviewed paper in *Science Advances*, was accomplished using a newly developed operational scenario dubbed Super I-mode. This regime maintains the high energy confinement characteristic of H-mode while avoiding large, transient heat loads on divertor components from edge-localized modes (ELMs). The discharge (shot #103986) exhibited a core electron temperature of approximately 4.9 keV and an energy confinement time of 0.11 seconds, sustained for a duration an order of magnitude longer than typical H-mode discharges. This demonstrates a viable solution for one of the primary challenges facing next-generation devices: steady-state operation. Source: Science Magazine

The Super I-mode is a significant advancement over the standard I-mode, which itself is an improvement on the widely used H-mode. While H-mode offers excellent energy confinement, it is plagued by ELMs that can erode plasma-facing components, a critical issue for reactors like ITER. The I-mode partially decouples particle and energy transport, suppressing large ELMs but often at the cost of reduced energy confinement. The Super I-mode achieved on EAST overcomes this trade-off by further optimizing plasma control. Researchers used a combination of upper single-null configuration and feedback-controlled lithium powder injection to manage particle exhaust and impurity levels, effectively creating a stable state with high energy confinement and low particle confinement, flushing impurities from the core without triggering major instabilities. Source: Science Magazine

The Super I-mode is a significant advancement over the standard I-mode, which itself is an improvement on the widely used H-mode.

Achieving this stable, long-pulse state required precise management of multiple plasma heating and control systems. The EAST experiment leveraged lower hybrid wave (LHW) heating, electron cyclotron resonance heating (ECRH), and ion cyclotron resonance heating (ICRH) to maintain the plasma temperature and current profile. A key innovation was the active feedback control of lithium powder injection. This technique conditioned the divertor target plates, reducing tungsten impurity influx and controlling the recycling of hydrogen isotopes at the plasma edge. This active wall conditioning was essential for preventing a radiative collapse or a transition back to a lower-confinement mode over the thousand-second timescale, showcasing a sophisticated level of integrated plasma control. Source: Science Magazine

The results from EAST provide critical data for the design and operation of future steady-state tokamaks, particularly China's planned China Fusion Engineering Test Reactor (CFETR). The demonstrated ability to sustain a high-performance plasma without large ELMs for over 15 minutes addresses a major engineering and physics challenge for reactor-scale devices. While the achieved plasma parameters, such as a normalized beta (β_N) of approximately 0.3, are modest compared to the requirements for a power plant, the duration and stability of the Super I-mode are highly relevant. The experiment validates a promising operational scenario that could be extrapolated to larger machines, potentially reducing the engineering burden on divertor and first-wall components. Source: Science Magazine