HL-2M

The HL-2M tokamak is a magnetic confinement fusion device operated by the Southwestern Institute of Physics (SWIP) in Chengdu, China. As a major upgrade to its predecessor, HL-2A, it represents a significant step in China's fusion energy research program. The device is designed to investigate key physics and engineering challenges relevant to next-generation fusion reactors like ITER and the proposed China Fusion Engineering Test Reactor (CFETR). Its primary research focuses on high-performance plasma operation, plasma-wall interactions, and the development of advanced divertor concepts to manage extreme heat loads.

Overview

HL-2M is characterized by its enhanced plasma parameters and operational flexibility compared to earlier Chinese tokamaks. With a major radius of 1.78 meters and a design plasma current of up to 3.0 mega-amperes (MA), it can achieve high-density, high-temperature plasmas. A key feature is its ability to generate plasmas with a more D-shaped cross-section (elongation κ ≈ 2.0) and significant triangularity (δ ≈ 0.5), which are crucial for achieving high-confinement modes (H-mode) and overall plasma stability. The device's mission is twofold: to contribute to the international fusion science community, particularly in support of ITER operations, and to build the domestic expertise and technological foundation required for a future fusion power plant. Its research campaigns are aimed at exploring advanced plasma scenarios, such as the I-mode and grassy Edge-Localized Mode (ELM) regimes, which offer potential solutions for steady-state operation in future reactors.

Physics and Mechanism

The operational capabilities of HL-2M are enabled by a combination of a powerful magnetic confinement system and substantial auxiliary heating. The toroidal field is generated by 20 copper coils, producing a field of up to 2.2 Tesla (T) on-axis. The poloidal field system provides robust plasma shaping and control, which is essential for accessing advanced divertor configurations.

A defining feature of HL-2M is its flexible divertor system. The divertor is designed to handle heat fluxes of up to 10 MW/m², comparable to those expected in ITER. The poloidal field coils allow for a wide range of magnetic geometries, including conventional single-null and double-null configurations, as well as more advanced concepts like the snowflake divertor. This flexibility allows scientists to experimentally test different strategies for spreading the heat load over a larger surface area, a critical challenge for any fusion reactor. The divertor targets are made of graphite, with plans for future upgrades to tungsten components to study materials relevant to a reactor environment.

To heat the plasma to fusion-relevant temperatures, HL-2M is equipped with a multi-faceted auxiliary heating and current drive system:

• Neutral Beam Injection (NBI): Two NBI lines are designed to inject a total of 13 MW of power, providing the primary source of plasma heating.
• Electron Cyclotron Resonance Heating (ECRH): An ECRH system, operating at 140 GHz, delivers up to 8 MW of power. This system is crucial for localized electron heating, plasma startup, and controlling magnetohydrodynamic (MHD) instabilities like neoclassical tearing modes (NTMs).
• Lower Hybrid Current Drive (LHCD): An LHCD system provides non-inductive current drive, essential for extending plasma duration and achieving steady-state operation.

The combination of these systems allows HL-2M to explore plasma regimes with ion and electron temperatures exceeding 100 million Kelvin (approximately 8.6 keV) and to push towards satisfying the Lawson criterion for net energy gain.

Historical Development

The HL-2M project is an evolution of a long-standing fusion research program at SWIP. Its direct predecessor, the HL-2A tokamak, operated from 2002 to 2018. HL-2A was itself constructed using major components from the German ASDEX (Axially Symmetric Divertor Experiment) tokamak, which were transferred to China in the late 1990s. This international collaboration provided a crucial foundation for China's tokamak research.

Building on the experience gained from HL-2A, the design and construction of HL-2M began in the 2010s. The project involved a complete rebuild of the machine, including a new vacuum vessel, new magnetic field coils, a more powerful power supply system, and upgraded heating and diagnostic systems. The goal was to significantly increase the plasma current, volume, and shaping capability to bridge the gap between existing devices and the requirements of ITER.

Construction of the HL-2M device was completed in 2019. Following a period of intensive commissioning and systems integration, the machine achieved its first plasma on December 4, 2020. This milestone marked the official start of its experimental operations and positioned China as a leading player in international fusion research.

Current Status

As of early 2026, HL-2M is in full operational mode, conducting regular experimental campaigns. The machine has successfully demonstrated stable H-mode operation with plasma currents exceeding 1 MA. Recent experiments have focused on optimizing plasma performance, mitigating ELMs, and characterizing the behavior of the flexible divertor. Researchers have achieved ion temperatures of over 150 million Kelvin in specific high-confinement scenarios, a significant achievement for a device of its class. According to a 2023 IAEA report, the device has routinely operated with 10 MW of auxiliary heating power, enabling detailed studies of plasma transport and stability under reactor-relevant conditions.

The diagnostic systems on HL-2M are comprehensive, providing high-resolution data on plasma temperature, density, confinement, and instabilities. This data is critical for validating theoretical models and improving predictive capabilities for future machines. Ongoing work includes the systematic exploration of advanced operational scenarios and the testing of novel divertor configurations to inform the design of CFETR and DEMO-class reactors.

Notable Implementations

HL-2M is the flagship device of the Southwestern Institute of Physics (SWIP), which is part of the China National Nuclear Corporation (CNNC). It operates in concert with other major Chinese fusion devices, such as the Experimental Advanced Superconducting Tokamak (EAST) in Hefei, which focuses on long-pulse, steady-state operation using superconducting magnets. The two machines have complementary missions: EAST pioneers long-duration plasmas, while HL-2M explores high-power, high-performance scenarios with a flexible conventional magnet design.

The research conducted on HL-2M directly supports the international ITER project. China is a full member of ITER, and the experiments on HL-2M provide valuable data on plasma control, heat exhaust, and operational scenarios that are directly applicable to ITER's research plan. Furthermore, the engineering and operational experience gained from HL-2M is fundamental to the design and eventual construction of the China Fusion Engineering Test Reactor (CFETR), which aims to be a next-step fusion device demonstrating a high tritium breeding ratio and electricity generation.

Open Challenges

Despite its successes, HL-2M faces several scientific and engineering challenges. A primary focus is managing the immense heat and particle fluxes to the divertor. While its flexible design allows for testing novel solutions, achieving a robust and reliable method for heat exhaust that can be extrapolated to a power plant remains a major research question. The graphite plasma-facing components currently used are subject to erosion and fuel retention, motivating a future transition to all-metal (tungsten) walls, which presents its own set of challenges related to plasma contamination and material damage.

Another key challenge is the control and mitigation of large-scale MHD instabilities, particularly ELMs, which can release bursts of energy that damage vessel walls. HL-2M is actively investigating techniques like resonant magnetic perturbations (RMPs) and pellet pacing to suppress or mitigate these events. Achieving stable, long-pulse H-mode operation at its full design current of 2.5–3.0 MA will require further optimization of the heating systems, plasma control algorithms, and wall conditioning techniques.

Outlook

The credible 5-15 year trajectory for HL-2M involves a phased approach to push its operational boundaries and address key reactor-relevant issues. In the near term (2026–2030), the focus will be on achieving the full design plasma current and heating power, systematically studying ELM mitigation techniques, and fully characterizing the performance of advanced divertor configurations like the snowflake. This phase will also involve initial experiments with tungsten plasma-facing components in the divertor region.

In the longer term (2030–2040), HL-2M is expected to serve as a testbed for integrated scenarios that combine high-performance core plasma with a reactor-compatible edge and divertor solution. It will play a crucial role in training the next generation of fusion scientists and engineers who will operate ITER and design CFETR. The results from HL-2M will be essential for validating the physics basis for CFETR's design, particularly in the areas of heat exhaust and steady-state operational scenarios. The device is poised to remain at the forefront of conventional-magnet tokamak research for at least the next decade, providing critical data for the global effort to realize fusion energy.

References

1. First plasma in China’s HL-2M tokamak — ITER Organization Newsline (2020)
2. Progress of the HL-2M Tokamak Project — IEEE Transactions on Plasma Science (2019)
3. Design and research progress of the HL-2M tokamak — Nuclear Fusion (2019)
4. Overview of the HL-2M project — Fusion Engineering and Design (2015)
5. China's 'artificial sun' tokamak sets new record — CGTN (2023)
6. Recent progress of the HL-2M tokamak experiments — Plasma Science and Technology (2022)
7. Fusion Devices — International Atomic Energy Agency (IAEA)
8. Design of the HL-2M ECRH system and recent progress — Fusion Engineering and Design (2021)