China tests world's largest fusion magnet: 582-tonne 'artificial sun' milestone explained

The 582-tonne superconducting magnet: key specifications

The D-shaped toroidal-field coil is the single largest and most powerful magnet ever built for a fusion device. Its key specifications include:

• Weight: 582 metric tonnes
• Dimensions: 21 metres long, 12 metres wide, and 3.3 metres tall
• Current: Carried a stable current of 60 kiloamperes during testing
• Stored energy: 6.03 megajoules per coil during testing
• Magnetic field strength: Approximately 6.5 tesla — roughly two to four times stronger than a hospital MRI
• Plasma confinement: Designed to confine plasma heated to over 100 million °C — around six times hotter than the Sun's core
• Lifespan: Designed for roughly 40,000 plasma pulses

Sixteen of these D-shaped coils will eventually be assembled together to form the toroidal magnetic field of the BEST reactor .

How it compares to ITER

The Chinese TF magnet outperforms the International Thermonuclear Experimental Reactor (ITER) equivalent in two key ways:

• Volume: 1.3 times the volume of ITER's TF magnets
• Stored energy: Roughly three times the stored energy of ITER's equivalent magnets

However, ITER remains a much larger overall machine (major radius of ~6.2 metres versus BEST's 3.6 metres) . BEST is not a full-scale ITER competitor — it is designed to be the world's largest operating deuterium-tritium tokamak prior to ITER, serving as a bridge between China's existing EAST tokamak and the much larger China Fusion Engineering Test Reactor (CFETR) .

A second key component: the central solenoid

Alongside the TF magnet, a central solenoid (CS) model coil also passed final tests under the CRAFT program . This assembly comprises both the toroidal-field magnet and the central solenoid coil . The central solenoid acts as the 'igniter' of the tokamak — it is critical for inducing and maintaining the plasma current . Researchers at ASIPP stated that the central solenoid "directly determines whether our fusion device can be started and kept running" .

Six years of domestic development

Both magnets were developed under China's Comprehensive Research Facility for Fusion Technology (CRAFT) project, a national big-science facility in Hefei . Key details:

• Development spanned approximately six years
• The magnets used entirely domestically made superconducting materials, structural designs, and manufacturing processes — with all core technologies achieving 100% domestic production
• The CRAFT facility was built specifically to develop and test full-scale fusion reactor components before installation in BEST

Timelines: BEST reactor and fusion electricity goals

China has laid out an aggressive timeline for its fusion program:

• BEST reactor construction: Began on June 30, 2023, and is scheduled for completion by the end of 2027
• First plasma: Expected in late 2027
• First fusion electricity: China aims to demonstrate fusion-generated electricity — often described as lighting the 'first fusion-powered lamp' — by around 2030
• Beyond BEST: The larger CFETR (China Fusion Engineering Test Reactor, also referred to as CFEDR) is projected to be operational around 2030, with commercial fusion power plants integrated into the grid targeted by later decades

According to The Economist, this timeline positions China roughly a decade ahead of other nations in the pursuit of fusion energy .