Experimental Advanced Superconducting Tokamak
The Experimental Advanced Superconducting Tokamak (EAST) is a magnetic confinement fusion research device located at the Institute of Plasma Physics, Chinese Academy of Sciences, in Hefei, Anhui Province, China. As the world's first fully superconducting tokamak with both toroidal and poloidal magnetic coils made from niobium-titanium superconductors, EAST is designed to explore steady-state, high-performance plasma operations essential for advancing fusion energy technologies, particularly in support of the International Thermonuclear Experimental Reactor (ITER) and the China Fusion Engineering Test Reactor (CFETR).[1][2] It features a non-circular plasma cross-section, actively water-cooled plasma-facing components, and configurations including lower single-null, double-null, and upper single-null divertors, enabling flexible experiments on plasma confinement, heating, and current drive.[1] EAST's key technical parameters include a major radius of 1.85 m (1.7–1.9 m depending on configuration), a minor radius of 0.4–0.45 m, an aspect ratio of approximately 4, a maximum plasma current of 1 MA, and a toroidal magnetic field up to 3.5 T (with a peak of 4 T at the coil center).[1] The device is equipped with a total heating power of over 34 MW from multiple systems, including 12 MW ion cyclotron resonance heating (ICRH), 10 MW lower hybrid current drive (LHCD), 8 MW neutral beam injection (NBI), and 4 MW electron cyclotron resonance heating (ECRH), all capable of continuous-wave operation to facilitate long-pulse discharges.[1] Proposed in 1996 and approved in 1998, construction began in October 2000, with first plasma achieved in October 2006 after assembly and commissioning by the Hefei-based team.[1][2] Since its inception, EAST has set numerous milestones in fusion research, including the first demonstration of 1 MA plasma current in a superconducting tokamak and early long-pulse diverted discharges reaching 100 seconds with central electron temperatures of 15 million degrees Celsius.[2] Notable achievements include a 403-second steady-state H-mode plasma in 2023 and, more recently, on January 20, 2025, sustaining a high-confinement plasma at over 100 million degrees Celsius for 1,066 seconds—over 2.5 times the 2023 record and advancing steady-state operation goals.[3][4] These accomplishments have validated technologies like superconducting magnets, divertor heat management, and plasma wall conditioning with lithium, while providing critical data for ITER's 400-second baseline and eventual 3,000–3,600-second operations.[1][4] Ongoing upgrades, such as enhanced heating power and diagnostics, continue to position EAST as a vital testbed for next-generation fusion reactors.[5]Development and History
Proposal and Construction
The Experimental Advanced Superconducting Tokamak (EAST) was proposed in 1996 by the Hefei Institutes of Physical Science, under the Chinese Academy of Sciences (CAS), specifically by the Institute of Plasma Physics (ASIPP), as China's inaugural fully superconducting tokamak aimed at advancing magnetic confinement fusion research.[1] This initiative sought to address key challenges in achieving long-pulse, high-performance plasma operations using superconducting technology, building on prior Chinese tokamak efforts like HT-6M and HT-7.[6] The project gained formal approval in July 1998 from China's National Development and Reform Commission, which allocated national funding to support its execution as a major science and engineering endeavor.[2] Construction officially began in October 2000 at the ASIPP site in Hefei, Anhui Province, involving coordinated efforts across multiple domestic institutions to integrate advanced engineering for a non-circular cross-section tokamak with all-superconducting magnets.[7] The endeavor drew on expertise from over 1,000 scientists, engineers, and technicians, highlighting China's growing capacity in fusion infrastructure development.[8] A primary engineering challenge centered on fabricating the superconducting toroidal field (TF) and poloidal field (PF) coils using niobium-titanium (NbTi) alloy in a cable-in-conduit configuration, cooled by supercritical helium at 4.2 K to enable stable, high-field operations essential for extended plasma confinement.[1] This required overcoming issues in coil winding, insulation, and cryogenic integration to achieve the necessary magnetic fields without quenching, representing a leap from earlier resistive magnet designs in Chinese devices.[9] Construction progressed through key milestones, including the delivery and installation of the vacuum vessel sectors in 2003, which formed the core enclosure for plasma operations after on-site welding.[6] By 2005, testing of the magnet system—encompassing 18 TF coils, a central solenoid, and 12 PF coils—confirmed performance under cryogenic conditions, with most units meeting design specifications prior to integration.[10] Full device assembly concluded in early 2006, paving the way for commissioning and first plasma later that year.[2] EAST's design also positioned it to support international efforts, such as providing validation data for the ITER project's superconducting magnet and steady-state operation requirements.[11]Operational Phases
The Experimental Advanced Superconducting Tokamak (EAST) initiated its operational Phase I in 2006 following the completion of construction. The device achieved its first plasma on September 28, 2006, in a limiter configuration, lasting nearly 3 seconds with a plasma current of 200 kA.[12] By January 2007, operations progressed to sustain 5-second pulses at 500 kA, focusing initially on basic plasma shaping, equilibrium control, and ohmic heating in hydrogen discharges.[12] Phase I continued through 2010, emphasizing foundational experiments with single-null and double-null divertor configurations, achieving elongations approaching 2, while leveraging the superconducting magnet system to enable extended pulse durations compared to conventional tokamaks.[13] Annual experimental campaigns during this period included periodic shutdowns for minor maintenance, building toward advanced heating integration. Phase II operations commenced in 2011 after a preparatory shutdown from late 2010, incorporating major upgrades to in-vessel components and auxiliary systems. Key enhancements included the replacement of carbon plasma-facing materials with molybdenum tiles on the first wall and the introduction of actively cooled upper and lower divertors, with the upper divertor upgraded to full tungsten plasma-facing components in 2014 and the lower divertor upgraded to full tungsten in 2021, to handle higher heat fluxes.[14][15] Further upgrades continued, including the installation of a full tungsten lower divertor in 2021 to enhance heat exhaust capabilities for longer pulses. Full resumption of experiments occurred in May 2014, following the completion of Phase II upgrades that boosted total heating and current drive capacity from 10 MW to 26 MW, including improvements to lower hybrid current drive (LHCD) systems for enhanced non-inductive current sustainment.[16] By 2018, electron cyclotron resonance heating (ECRH) was integrated into campaigns, adding up to 0.5 MW initially, with designs supporting 4 MW at 140 GHz for long-pulse steering. This phase has emphasized iterative advancements in steady-state capabilities, with annual campaigns typically spanning 2-3 months each, interspersed with maintenance shutdowns, and evolving to multi-year operational schedules post-2020 to support extended testing sequences.[17]Design and Technical Features
Tokamak Configuration
The Experimental Advanced Superconducting Tokamak (EAST) employs a conventional tokamak geometry with a major radius of 1.85 m and a minor radius of 0.45 m, yielding an aspect ratio of approximately 4.11.[18] The plasma cross-section is D-shaped and elongated, capable of achieving elongations up to 2.0 and triangularities up to 0.8 to enhance stability and confinement properties.[18] The vacuum vessel is a double-walled stainless steel torus, standing approximately 8 m tall, which serves as the primary containment for the plasma and supports internal components while maintaining structural integrity under operational loads.[10] It features a baking system that heats the vessel to 150°C to desorb impurities and achieve high plasma purity.[19] The torus volume measures 38 m³, with a base pressure of 1×10^{-7} Pa ensured by the integrated vacuum pumping system for ultra-high vacuum conditions. EAST's divertor system utilizes an advanced double-null configuration to manage heat and particle exhaust effectively, supporting versatile operational modes such as upper or lower single-null and pump limiter setups. The first wall is protected by carbon fiber composite tiles, while the divertor targets consist of tungsten components installed starting in 2014 to withstand high heat fluxes exceeding 10 MW/m².[20] This plasma-facing material choice facilitates long-pulse operations while minimizing impurity contamination.[20] The overall configuration integrates seamlessly with the surrounding superconducting magnet system to enable precise plasma shaping and positioning.[18]Superconducting Magnet System
The superconducting magnet system of the Experimental Advanced Superconducting Tokamak (EAST) is a fully superconducting design, marking it as the world's first tokamak with both toroidal field (TF) and poloidal field (PF) magnets constructed from superconductivity materials. This system generates the necessary magnetic fields for plasma confinement and shaping, enabling advanced steady-state operations. Comprising 16 D-shaped TF coils and 14 PF coils (including a central solenoid assembly), the magnets utilize niobium-titanium (NbTi) cable-in-conduit conductor (CICC) technology for high stability and current capacity.[1][21] The TF coils, each weighing approximately 16 tons with a total conductor length exceeding 20 km, produce a central toroidal magnetic field of 3.5 T at an operating current of 14.3 kA, storing about 200 MJ of energy. These coils are wound with NbTi strands featuring a copper-to-non-copper ratio greater than 1, encased in stainless steel jackets, and insulated to withstand 10 kV. The PF coils, totaling 14 units arranged for plasma shaping and positioning, support non-inductive current drive by providing flexible poloidal fields; they include six central solenoid coils tested at ramp rates up to 100 kA/s. All coils incorporate quench detection and protection systems using external dump resistors and DC circuit breakers to safely dissipate energy during potential superconducting transitions, ensuring operational safety over extended pulses.[1][22][23][24] The cryogenic system cools the magnets to 4.2 K using forced-flow supercritical helium, with a refrigeration capacity of approximately 2 kW at 4.5 K, supplemented by higher-temperature stages for thermal shields. This setup maintains superconducting stability while minimizing heat loads from pulsed operations. The coils were fabricated primarily at the Institute of Plasma Physics, Chinese Academy of Sciences (ASIPP), utilizing domestically developed CICC jacketing lines and winding machines, with technology transfer from international partners; prototype testing in 2005 achieved stable operation up to 4.0 T. Compared to traditional copper resistive magnets, which consume megawatts of electrical power, EAST's superconducting system reduces ongoing power needs to kilowatt levels for cryogenics alone, facilitating long-pulse (over 1000 s) high-confinement plasma experiments and supporting ITER-like steady-state research.[19][23][1]Heating and Current Drive Systems
The heating and current drive systems of the Experimental Advanced Superconducting Tokamak (EAST) provide auxiliary power to initiate and sustain plasma discharges, enabling non-inductive current drive and advanced confinement regimes such as H-mode. These systems collectively deliver over 30 MW of power, supporting long-pulse operations by compensating for the limitations of inductive current drive from the central solenoid. Key challenges in integration include maintaining high antenna coupling efficiency above 90% to minimize reflected power and ensure stable operation, particularly under varying plasma densities and edge conditions.[25][26][1] The lower hybrid current drive (LHCD) system operates at dual frequencies of 2.45 GHz and 4.6 GHz, delivering up to 10 MW of power (4 MW at 2.45 GHz and 6 MW at 4.6 GHz) using multiple klystrons to generate non-inductive plasma currents up to 1 MA, primarily for off-axis current profile control and steady-state scenarios. This system employs a passive-active multijunction launcher for the 2.45 GHz component, optimized for edge current drive, and a multi-junction grill for the 4.6 GHz portion, facilitating efficient wave absorption in the plasma core. LHCD plays a critical role in achieving H-mode transitions by providing the necessary current sustainment without relying on inductive methods.[25][27][28] Ion cyclotron resonance heating (ICRH) contributes up to 12 MW at frequencies tunable between 25 and 70 MHz, utilizing four antennas configured for minority ion heating schemes, such as hydrogen in deuterium plasmas, to heat ions efficiently in the central plasma region. The antennas feature actively cooled structures to handle high heat loads, with the system designed for robust coupling even in low-density edge plasmas.[29][30][19] Electron cyclotron resonance heating (ECRH), upgraded after 2018, provides up to 4 MW at 140 GHz using gyrotrons for precise, localized electron heating and current drive, particularly useful for neoclassical tearing mode stabilization and off-axis current profiling. The system includes transmission lines and a steerable launcher to target specific plasma locations.[31][32][33] Neutral beam injection (NBI) provides up to 8 MW using two deuterium beamlines at energies of 50–80 keV, aimed at core heating and toroidal momentum input, with routine operation supporting full-power discharges. The injectors are configured for tangential injection to optimize current drive efficiency.[34][35]Research Objectives
Plasma Confinement Goals
The Experimental Advanced Superconducting Tokamak (EAST) aims to achieve high-confinement mode (H-mode) operation to enhance plasma energy confinement, targeting an energy confinement time exceeding 1 second at safety factor values q95 between 3 and 5, in alignment with ITER baseline scenarios. This regime forms an edge transport barrier that reduces turbulent losses, enabling higher plasma density and temperature profiles essential for fusion performance. EAST's flexible heating systems facilitate H-mode access across a range of plasma currents up to 1 MA, with normalized confinement enhancement factors H98(y,2) greater than 1.0 routinely pursued to validate scaling laws for reactor-relevant conditions.[36][37] A key focus is the control of plasma instabilities to maintain confinement quality, particularly suppressing edge-localized modes (ELMs) and neoclassical tearing modes (NTMs) using resonant magnetic perturbations (RMPs). ELMs, which cause intermittent heat bursts to the divertor, are targeted for mitigation or suppression through n=3 or n=4 RMP coils, achieving full ELM suppression in low-torque plasmas at q95 ≈ 3.6 without significant confinement degradation. Similarly, NTMs are addressed via RMPs combined with electron cyclotron current drive (ECCD), stabilizing m/n=2/1 islands by reducing their seed widths and enhancing bootstrap current alignment, thereby preventing performance-limiting disruptions. These efforts support ITER validation by demonstrating stable operation in ELM-free or mitigated H-mode over extended periods.[38][39][40] EAST targets normalized beta values (βN) up to 2.0 to maximize fusion power density while avoiding disruptions, corresponding to poloidal beta βp ≈ 2–3 in high-performance discharges. This limit is pursued in high-triangularity configurations with balanced current drive, where βN ≈ 1.8–2.0 has been integrated with H-mode pedestals to achieve stored energies around 220 kJ without neoclassical MHD instabilities dominating transport. Such operations provide critical data on beta scaling with density and heating profiles, informing limits for steady-state reactors.[37][36] In divertor physics, EAST investigates heat flux mitigation strategies to keep peak loads below 10 MW/m² on plasma-facing components during long-pulse H-mode, using techniques like impurity seeding (neon-deuterium mixtures) and snowflake divertor geometries. These approaches reduce parallel heat flux by promoting partial detachment, with peak fluxes controlled to 3–5 MW/m² in mitigated ELM scenarios, while preserving core confinement. This work validates power exhaust solutions for ITER-like conditions, emphasizing compatibility with high βN and q95 ranges.[37][41] Theoretically, EAST serves as a platform for validating gyrokinetic simulations of turbulence and transport, using codes like GYRO to model ion-temperature-gradient (ITG) and trapped-electron-mode (TEM) driven fluctuations against experimental profiles. These simulations confirm transport coefficients in high-βp H-mode plasmas (βp ∼ 3), reproducing pedestal stability and core anomalous transport with errors below 20%, thus benchmarking models for predictive extrapolation to ITER and beyond.[42][43]Long-Pulse and Steady-State Operation
The Experimental Advanced Superconducting Tokamak (EAST) is designed to explore long-pulse and steady-state plasma operations, which are essential for demonstrating the feasibility of continuous fusion reactor performance without reliance on inductive current drive from the central solenoid.[44] These objectives focus on sustaining high-temperature plasmas for durations approaching or exceeding those required for practical fusion devices, integrating non-inductive current drive mechanisms to maintain plasma equilibrium over extended periods.[1] EAST's pulse length targets include achieving 400 seconds of operation at a plasma current of 1 MA in H-mode, with potential extension to 1000 seconds at 0.5 MA, enabling tests of prolonged plasma stability and confinement.[44] Full non-inductive operation is a core goal, aiming for greater than 50% bootstrap current fraction to minimize external power requirements and support self-sustaining plasma currents. In steady-state scenarios, EAST integrates lower hybrid current drive (LHCD) with bootstrap currents to achieve zero-loop-voltage operation, where the plasma current is entirely sustained by non-inductive means, targeting electron temperatures exceeding 70 million degrees Celsius to mimic reactor-relevant conditions.[45] This approach ensures flat-top phase stability, allowing consistent plasma parameters over the discharge duration without inductive flux consumption.[46] Power exhaust management is critical for these long durations, with EAST designed to maintain divertor detachment to handle heat fluxes effectively over 1000 seconds, preventing material damage while preserving core plasma performance.[47] Current drive efficiency is targeted at \eta_{CD} > 0.3 \times 10^{19} \, \mathrm{A/W/m^2} for LHCD systems, optimizing energy input for sustained operation.[48] These efforts hold direct relevance to ITER, as EAST tests steady-state regimes at comparable aspect ratios and safety factor (q) profiles, providing validation for non-inductive sustainment in superconducting tokamaks.[1]Key Parameters and Diagnostics
Core Specifications
The Experimental Advanced Superconducting Tokamak (EAST) operates within defined quantitative limits that enable its research into advanced plasma confinement. These core specifications encompass geometric, magnetic, plasma, and operational parameters, as detailed in the following table.[49][50][51]| Parameter | Value/Range | Description/Notes |
|---|---|---|
| Aspect ratio (R/a) | 4.11 | Ratio of major to minor radius, defining the tokamak's geometry. |
| Plasma volume | ~6 m³ | Approximate volume of confined plasma. |
| Toroidal magnetic field (B_t) | 3.5 T | Maximum on-axis field generated by superconducting toroidal field coils. |
| Poloidal magnetic field (B_p) | Up to 1 T | Field from poloidal coils and plasma current, enabling shaping. |
| Safety factor (q_{95}) | 2–10 | Edge safety factor, variable for stability studies. |
| Plasma current (I_p) | 1.0 MA (maximum) | Peak toroidal current in the plasma. |
| Electron density (n_e) | 1–10 × 10^{19} m^{-3} | Line-averaged range across discharges. |
| Central electron temperature (T_e(0)) | 100 million °C (~8.6 keV) | Achieved in high-performance regimes. |
| Total heating power | 32 MW | Combined input from RF and other systems including ICRH, LHCD, NBI, and ECRH for advanced operations.[49] |
| Pulse duration | 1–>1000 s | From short pulses to steady-state attempts, with 1066 s achieved as of January 2025.[4] |
| Plasma elongation (κ) | 1.6–2.0 | Vertical extension of plasma cross-section. |
| Plasma triangularity (δ) | 0.6–0.8 | Measure of plasma cross-section shaping for confinement optimization. |