Here’s what you’ll learn when you read this story:
The central solenoid is the heart of a fusion reactor, and a “jacket” of meticulously crafted stainless steel—capable of withstanding extreme temperatures and magnetic fields—protects it.
Chinese scientists say that a new super steel, called China high-strength low-temperature steel No. 1, (CHSN01), can operate at a maximum of 20 Tesla, which outperforms the steel jacket that will be used by ITER.
China is incorporating CHSN01 into its Burning Plasma Experiment Superconducting Tokamak (BEST) and will likely play a role in future fusion projects well into the future.
The biggest unknown in fusion energy isn’t the physics powering gargantuan reactors known as tokamaks. Scientists are confident that if a reactor contains a superheated plasma, fueled by heavy hydrogen isotopes of deuterium and tritium, at temperatures approaching 100 million degrees Celsius, you will produce a self-sustaining reaction, generating near endless amounts of clean energy. Tokamaks around the world—not to the National Ignition Facility’s successful fusion ignition in 2022—have proven this out time and again.
The real problem is the materials needed to build the thing.
“You need a material solution. Give me the materials that can hold this thing together, at temperature, to be efficient,” Phil Ferguson, Ph.D., Director of the Material Plasma Exposure eXperiment (MPEX) Project at Oak Ridge National Laboratory told Popular Mechanics in 2024. “We are still lacking a breakthrough in materials.”
Not only does a fusion reactor need parts, such as the divertor, to handle the plasma’s extreme heat, other parts of the very same machine need to withstand and operate at temperatures approaching absolute zero. One of these parts is the very heart of the reactor, called the central solenoid, which is responsible for a majority of the magnetic flux to generate the plasma and is powered by ultracold cable-in-conduit superconductors. The shield, or jacket, for the central solenoid needs to be a steel material that can retain superior mechanical and thermal properties at cryogenic temperatures while also withstanding intense magnetic fields.
The International Thermonuclear Experimental Reactor (ITER), the world’s most advanced tokamak that’s due for first plasma by 2034, uses a material known as 316LN stainless steel designed to operate at a maximum of 11.8 Tesla. Now, a new report from the state-run South China Morning Post (SCMP) suggests that Chinese scientists have come up with a new material that has even ITER’s steel jacket of choice beat. This super steel, called China high-strength low-temperature steel No. 1, or CHSN01, can withstand up to 20 Tesla and 1,500-megapascal (MPa) of stress. Scientists detailed the 12-year process to create this particular steel jacket in the journal Applied Sciences this past May.
“While ITER’s maximum 11.8 Tesla field design is enough for itself, future higher-field magnets will require advanced materials,” said Li Laifeng, a researcher at the Chinese Academy of Sciences’ (CAS), reports SCMP. “Developing next-gen cryogenic steel isn’t optional – it’s essential for the success of China’s compact fusion energy experimental devices.”
CHSN01 will be in the central Solenoid of China’s Burning Plasma Experiment Superconducting Tokamak (BEST), an intermediary reactor between the country’s first-generation fusion reactors and the Chinese Fusion Engineering Test Reactor—the country’s first fusion plant demonstrator. Scientists aim for the BEST reactor to achieve first plasma in late 2027.
Having grasped the particulars of fusion physics, we’re now crafting the materials to make it possible.
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