BEST (Burning Plasma Experimental Superconducting Tokamak)

Overview

The Burning Plasma Experimental Superconducting Tokamak (BEST) is a proposed next-generation fusion energy device under conceptual design by the Institute of Plasma Physics, Chinese Academy of Sciences (ASIPP). As a key component of China's national fusion energy roadmap, BEST is designed to be a large-scale, fully superconducting tokamak aimed at achieving and sustaining a burning plasma. Its primary scientific objective is to explore the physics of self-heated plasmas where alpha particles from deuterium-tritium (D-T) reactions provide the dominant source of plasma heating, a condition characterized by a plasma energy gain factor (Q_plasma) greater than 10.

BEST is strategically positioned to operate in parallel with or subsequent to ITER, leveraging insights from its construction and operation while focusing on the specific challenges of steady-state operation and technologies required for a Demonstration Power Plant (DEMO). Key goals include demonstrating long-pulse, high-performance plasma scenarios, testing advanced divertor concepts for power exhaust management, and developing a closed tritium fuel cycle, including a functional tritium breeding blanket. The device represents a critical step in validating the integrated physics and engineering required for a commercially viable fusion power plant.

Physics / Mechanism

The BEST design is based on established tokamak physics, scaled to a regime capable of sustaining a burning plasma. The proposed parameters include a major radius (R) of approximately 7.2 m, a minor radius (a) of 2.2 m, and a high toroidal magnetic field (B_t) of 6.5 T on-axis. This high field, generated by niobium-tin (Nb3Sn) superconducting magnets, is crucial for confining a high-pressure plasma, as the achievable plasma pressure scales with B_t². The device is designed to support a plasma current (I_p) of up to 10 MA, which is essential for achieving the required energy confinement time according to empirical scaling laws like the H-mode scaling (τ_E ∝ I_p).

The combination of these parameters is intended to achieve a triple product (n·τ·T) well in excess of the Lawson criterion for ignition. The target operational scenario is a high-confinement mode (H-mode) plasma with a normalized beta (β_N) around 2.5 and a high bootstrap current fraction (f_BS) of approximately 50%. A high bootstrap fraction is a cornerstone of the steady-state mission, as this self-generated current reduces the need for external current drive, thereby improving the overall power plant efficiency.

To reach these conditions, BEST will be equipped with a powerful suite of auxiliary heating and current drive (H&CD) systems, totaling over 100 MW. This includes Neutral Beam Injection (NBI) for core heating and current drive, Electron Cyclotron Resonance Heating (ECRH) for localized heating and magnetohydrodynamic (MHD) instability control, and Ion Cyclotron Resonance Heating (ICRH) for ion heating. The primary challenge in a burning plasma is managing the immense power exhaust. BEST's design incorporates an advanced divertor, likely a double-null or a long-legged single-null configuration, to spread the heat load over a larger surface area and facilitate plasma detachment, thereby protecting plasma-facing components.

Historical Development

The conceptualization of BEST is the culmination of decades of research and operational experience from China's domestic fusion program, centered at ASIPP. The program's progression follows a clear path of increasing scale and technological sophistication. The foundation was laid by the HT-7 tokamak, a device retrofitted with superconducting magnets in the 1990s, which provided the initial experience in operating such systems.

This was followed by the highly successful Experimental Advanced Superconducting Tokamak (EAST), which came online in 2006. EAST was the first fully superconducting tokamak with a non-circular cross-section and has been a world-leading platform for investigating long-pulse, high-performance plasma scenarios. Key milestones achieved on EAST directly inform the BEST design and its operational goals. These include the demonstration of a 1056-second long-pulse H-mode discharge in 2021 and achieving plasma temperatures exceeding 100 million K. The extensive operational data from EAST on plasma control, RF heating, and divertor physics provides a critical, experimentally validated basis for the design and risk mitigation of BEST.

The conceptual design of BEST began in the late 2010s, evolving from earlier concepts for a Chinese Fusion Engineering Test Reactor (CFETR). The design has matured through several phases, incorporating global developments in fusion science, particularly lessons from the ITER project. The decision to pursue a dedicated burning plasma experiment like BEST reflects a strategic choice to build a national capability in the integrated physics and technology of a self-sustaining fusion system.

Current Status

As of early 2026, BEST remains in the advanced conceptual and engineering design phase. The ASIPP team, in collaboration with other Chinese institutions, is finalizing the physics basis and key engineering specifications. This work involves extensive modeling and simulation of plasma scenarios, MHD stability, and power exhaust using codes benchmarked against experiments on EAST and other devices worldwide. The R&D program is focused on critical components, such as high-field Nb3Sn superconducting magnets, advanced divertor materials, and prototypes for the tritium breeding blanket test modules.

The project has not yet received final government approval for construction, and a definitive timeline has not been publicly announced. The decision to proceed will depend on the finalization of the engineering design, successful validation of key technologies through the R&D program, and national strategic planning. The project is often discussed in the context of China's long-term energy strategy and its ambition to be a leader in commercial fusion energy. The progress of the ITER project is also a significant factor, as operational data from ITER will be invaluable for refining the final design and operational plan for BEST.

Notable Implementations

BEST is a singular, national-scale project led by the Institute of Plasma Physics, Chinese Academy of Sciences (ASIPP) in Hefei. ASIPP is the primary institution responsible for the design, R&D, and eventual construction and operation of the device. It leverages the extensive expertise and infrastructure developed for the EAST tokamak.

The project involves a broad collaboration of universities and research institutes across China, contributing to specific areas such as materials science, magnet technology, plasma theory, and diagnostics. While it is a national project, the design and R&D efforts benefit from international collaborations and information exchange within the global fusion community, including participation in International Tokamak Physics Activity (ITPA) working groups and other forums. The development of BEST is a central pillar of the Chinese fusion program, intended to be the direct predecessor to a Chinese DEMO reactor, which aims to produce net electricity for the grid.

Open Challenges

Despite the strong foundation provided by EAST, the BEST project faces significant scientific and engineering challenges inherent in any burning plasma device. A primary challenge is managing the extreme heat and particle fluxes on the divertor and first wall. The expected steady-state heat load of >10 MW/m² presents a severe materials science challenge, requiring advanced tungsten-based materials and innovative cooling technologies to prevent component failure.

Another critical area is the physics of a self-heated plasma. The behavior of a plasma dominated by alpha heating is not fully understood. Potential issues include the excitation of new instabilities by the energetic alpha particle population, such as Toroidal Alfvén Eigenmodes (TAEs), which could degrade confinement and potentially damage vessel components. Developing robust control schemes to maintain plasma stability and performance in this new regime is a key research goal.

From an engineering perspective, the fabrication and quality control of the large, high-field Nb3Sn superconducting magnets are formidable tasks. These magnets must operate reliably for long durations under high mechanical and thermal stresses. Furthermore, achieving a closed tritium fuel cycle with a tritium breeding ratio (TBR) greater than 1 is essential for a sustainable fusion power plant. BEST will serve as a testbed for tritium breeding blanket modules, but demonstrating a net production of tritium in a realistic reactor environment remains a major unresolved challenge for the entire fusion field.

Outlook

Assuming government approval and funding are secured in the near future, the construction of BEST could potentially begin around 2030, with first plasma operations anticipated in the late 2030s or early 2040s. This timeline would position BEST to operate concurrently with or immediately following the main D-T campaign at ITER, allowing it to build directly upon ITER's scientific results.

In the next 5-10 years, the primary focus will be on completing the engineering design and executing the associated R&D program. This includes constructing and testing full-scale magnet prototypes and developing advanced plasma-facing components and divertor solutions. The results of these R&D efforts will be critical for finalizing the machine's design and mitigating construction risks.

If successful, BEST will provide the world with a second facility, after ITER, capable of studying burning plasma physics. Its specific focus on steady-state operation and DEMO-relevant technologies will be a crucial step toward the realization of commercial fusion energy. The data and operational experience from BEST would directly inform the design of China's DEMO, potentially accelerating the timeline for a fusion power plant to be connected to the grid, which is targeted for the 2050s under China's current roadmap.

References

1. Progress of the Steady-State Operation of EAST and the Proposal of BEST — Nuclear Fusion (2022)
2. Overview of the present progress and activities on the Chinese Fusion Engineering Test Reactor — Nuclear Fusion (2020)
3. Design and R&D progress of the Chinese Fusion Engineering Test Reactor — Fusion Engineering and Design (2019)
4. Concept design of the BEST tokamak for burning plasma experiment — Plasma Science and Technology (2024)
5. Realization of a fully non-inductive steady-state scenario with high confinement and high bootstrap fraction on EAST — Physical Review Letters (2022)
6. China's new 'artificial sun' project to be operational by 2035 — South China Morning Post (2023)
7. Overview of the EAST project — Fusion Engineering and Design (2006)