EAST (Experimental Advanced Superconducting Tokamak)

Overview

The Experimental Advanced Superconducting Tokamak (EAST), or Hefei Tokamak-7U (HT-7U), is a major magnetic confinement fusion experiment operated by the Institute of Plasma Physics of the Chinese Academy of Sciences (ASIPP). As one of the world's first fully superconducting tokamaks, its primary mission is to investigate the scientific and technological challenges of steady-state plasma operation. EAST's research directly supports the operational goals of larger next-generation devices like ITER and informs the design of the proposed China Fusion Engineering Test Reactor (CFETR). The device is notable for its flexible heating and current drive systems and its advanced divertor configurations, which have enabled it to achieve world-record pulse durations for high-confinement mode (H-mode) plasmas.

Physics / Mechanism

EAST is a D-shaped cross-section tokamak that utilizes superconducting magnets to generate the magnetic fields required for plasma confinement. This design choice is central to its mission of achieving long-pulse operation.

Superconducting Magnet System: Unlike tokamaks with copper magnets that have high electrical resistance and must be operated in short pulses to avoid overheating, EAST employs Niobium-Titanium (NbTi) superconductors for all its main coils: 16 D-shaped toroidal field (TF) coils and 12 poloidal field (PF) coils, including the central solenoid. These coils are cooled to 4.5 K with supercritical helium, allowing them to carry large currents with near-zero resistance. This capability is the foundation for maintaining stable magnetic fields and plasma confinement for extended periods, far exceeding the limits of resistive-magnet machines.

Plasma Facing Components (PFCs): The materials facing the hot plasma are critical for managing extreme heat loads and minimizing plasma contamination. EAST's PFCs have evolved significantly. The initial configuration used molybdenum and graphite tiles. To better handle the high heat fluxes of long-pulse H-mode operation, EAST was upgraded with an ITER-like tungsten divertor. Tungsten offers a high melting point and low sputtering yield, reducing the influx of impurities into the plasma core. The first wall is actively water-cooled to dissipate heat during multi-minute discharges.

Heating and Current Drive (H/CD): To reach fusion-relevant temperatures and sustain the plasma current non-inductively, EAST is equipped with a versatile and powerful suite of H/CD systems:

• Lower Hybrid Current Drive (LHCD): A primary tool for driving current in the outer region of the plasma, essential for achieving a steady-state current profile.
• Ion Cyclotron Resonance Heating (ICRH): Heats plasma ions by launching radio-frequency waves at their resonant frequency.
• Electron Cyclotron Resonance Heating (ECRH): Heats electrons and can be used for localized current drive and MHD instability control.
• Neutral Beam Injection (NBI): Injects high-energy neutral particles that ionize within the plasma, transferring their energy and momentum to heat the plasma and drive current.

The combination of these systems provides the flexibility to control the plasma temperature, density, and current profiles, which is necessary for exploring advanced operating scenarios.

Historical development

EAST represents the third generation of tokamaks at ASIPP, following the Hefei Tokamak-6 (HT-6) series and the Hefei Tokamak-7 (HT-7), which was itself an upgrade of the Russian T-7 tokamak. The decision to build a fully superconducting device was made in the late 1990s to position China at the forefront of steady-state fusion research.

• 1998: The EAST project was formally approved by the Chinese government.
• 2000-2005: Construction of the main device components, including the complex superconducting magnet system and vacuum vessel, was completed. This phase involved significant domestic research and development in large-scale superconductor manufacturing and cryogenics.
• 2006: EAST achieved its first plasma in September, marking its successful commissioning.
• 2010-2012: Major upgrades were implemented, including the installation of the LHCD system and initial high-power ICRH experiments.
• 2014: An upper single-null divertor with tungsten PFCs was installed, beginning the transition to an ITER-like operational environment.
• 2017: EAST sustained an H-mode plasma for over 100 seconds, a world record at the time, demonstrating the viability of long-pulse high-performance operation. This achievement relied on the effective integration of its superconducting magnets and auxiliary heating systems.
• 2021: The machine achieved a plasma temperature of 120 million K for 101 seconds. Later that year, it set a new world record for pulse duration, maintaining a 70 million K plasma for 1,056 seconds (17.6 minutes).

These milestones have progressively expanded the operational envelope for steady-state tokamaks and provided critical data for the international fusion community.

Current status

As of 2026, EAST continues to operate as a leading global platform for steady-state fusion science. Its research program is focused on integrating high-performance core plasmas with effective solutions for heat and particle exhaust at the plasma edge. Key research areas include:

• Steady-State H-mode Scenarios: Pushing the duration and performance of H-mode discharges, aiming for a fully non-inductive state where 100% of the plasma current is driven by external sources. This is a direct demonstration of a key operational mode for a future fusion power plant.
• Divertor Physics and PFCs: Testing the performance and longevity of the tungsten divertor under reactor-relevant heat fluxes (approaching 10 MW/m²). This research is vital for validating material choices and exhaust strategies for ITER.
• Plasma Control: Developing advanced feedback control algorithms to manage plasma profiles and suppress magnetohydrodynamic (MHD) instabilities like Edge Localized Modes (ELMs) over long timescales.
• Integrated Scenarios: Combining a high-performance core (high temperature and density) with a detached or partially detached divertor plasma to reduce heat loads on PFCs, a necessary condition for a commercially viable reactor.

EAST collaborates extensively with international partners, including the ITER Organization and research teams from the US, EU, and Japan, often serving as a testbed for hardware and operational techniques.

Notable implementations

The EAST facility itself is the implementation. Its unique character is defined by the integration of several key subsystems that collectively enable its long-pulse mission:

• Fully Superconducting Magnets: EAST was the first tokamak to feature both toroidal and poloidal field magnets made from superconductors (NbTi). This design choice, shared by South Korea's KSTAR, distinguishes it from earlier large tokamaks like JET (copper) and provides the foundation for its steady-state research program.
• ITER-like Tungsten Divertor: The upgrade to an actively-cooled tungsten divertor mimics the material and design philosophy of the ITER divertor. This allows for direct experimental validation of heat exhaust solutions under long-pulse conditions, providing critical data on material erosion, redeposition, and fuel retention.
• Advanced H/CD Portfolio: The combination of four distinct heating and current drive systems (LHCD, ICRH, ECRH, NBI) provides exceptional control over the plasma. Researchers can tailor the deposition of power and current to optimize performance, control instabilities, and sustain the plasma for extended periods without relying on the central solenoid's inductive current drive.

Open challenges

Despite its successes, EAST faces significant scientific and engineering challenges that are common to the pursuit of steady-state fusion:

• Heat Exhaust Management: Managing the immense, steady-state heat flux onto the divertor remains the primary challenge. While the tungsten divertor is a major advance, achieving a stable, fully detached divertor plasma simultaneously with a high-performance core plasma is an ongoing area of intense research. The power handling limit of the PFCs is a key constraint on achievable pulse length and performance.
• Impurity Control: In long discharges, impurities eroded from the wall and divertor can accumulate in the plasma core, radiating energy and diluting the fusion fuel. Developing techniques to prevent impurity accumulation without degrading overall confinement is critical.
• Integration of Core and Edge Solutions: The conditions required for optimal core plasma performance (high temperature, steep pressure gradients) are often in conflict with the requirements for the plasma edge (low temperature, high radiation to spread heat). Finding integrated scenarios that satisfy both core and edge constraints simultaneously is a central goal of the EAST program and the broader fusion community.
• Disruption Prediction and Mitigation: While less frequent in some advanced scenarios, plasma disruptions pose a risk to the machine. Developing reliable real-time prediction and mitigation systems is essential for protecting the device during high-power, long-pulse experiments.

Outlook

In the next 5-15 years, EAST is positioned to continue making critical contributions to fusion energy development. The near-term focus will be on achieving fully non-inductive, steady-state H-mode operation for pulse lengths exceeding 1,000 seconds with improved performance parameters, including higher plasma density and confinement quality. This involves further optimization of the H/CD systems and plasma control schemes.

EAST will serve as a crucial testbed for technologies and operational scenarios for the China Fusion Engineering Test Reactor (CFETR), a planned next-generation device intended to demonstrate fusion energy production at the level of hundreds of MW. The experimental results from EAST, particularly regarding heat exhaust, plasma control, and steady-state sustainment, will directly inform CFETR's engineering design and operational plan.

Furthermore, as ITER begins operations, EAST will provide a valuable platform for training a new generation of scientists and engineers in the operation of a fully superconducting tokamak, and for testing control strategies and diagnostics in a relevant plasma environment before their implementation on the larger, more powerful machine.

References

1. Mission and main design of EAST project — Plasma Science and Technology (2006)
2. Overview of the latest EAST experiments — Nuclear Fusion (2017)
3. Recent advances in EAST experiments — Nuclear Fusion (2022)
4. China's 'artificial sun' tokamak sustains plasma at 120 million°C for 101 seconds — Physics World (2021)
5. China's 'artificial sun' sets new world record — Xinhua News Agency (2021)
6. Progress of the EAST project in China — Fusion Engineering and Design (2007)
7. Development of steady-state scenarios for long-pulse H-mode operation on EAST — Nuclear Fusion (2019)