World’s largest nuclear fusion reactor achieves first plasma

JT-60SA will also help ITER, the giant international fusion reactor that is being built in France, to demonstrate that fusion can produce more energy than it consumes.

T-60SA after completion of assembly of related components.

Japan's new fusion reactor, JT-60SA, which confines a hot plasma in a doughnut-shaped chamber using superconducting magnets, has been successfully turned on. The largest and most sophisticated reactor in the world, it supports the international Thermonuclear Experimental Reactor (ITER) project in France and studies the physics of fusion energy.

On October 26, 2023, the first plasma was produced following over 15 years of development and testing. "This demonstrates to the world that the apparatus performs its intended function," stated Fusion for Energy project manager Sam Davis. Regarding JT-60SA and related programmes, this EU organisation works with the National Institutes for Quantum Science and Technology (QST) in Japan.

What is JT-60SA?

Unlike earlier large tokamaks, the reactor is intended to heat the plasma to 200 million degrees Celsius and hold it there for roughly 100 seconds. This will enable scientists to look into ways to regulate and enhance the performance and stability of the plasma, which are essential for producing fusion power.

Additionally, JT-60SA will support ITER, the massive international fusion reactor under construction in France, in proving that fusion energy can generate more energy than it consumes. ITER will be dependent on operational expertise and technologies that JT-60SA will verify and test.

Japan was granted permission to construct JT-60SA and two additional smaller fusion facilities in exchange for France being allowed to host ITER, the largest fusion experiment in history. This was a component of a 2007 deal between the EU and Japan, which also included modernising Japan's outdated JT-60 reactor, which has been operational since the middle of the 1980s. The cost of the reactor's total rebuild, which started from scratch, was kept a secret.

"Superadvanced" refers to JT-60SA, which is roughly half the height of ITER. One-sixth of what ITER can hold, or 135 cubic metres, of plasma can be stored there. Alberto Loarte, head of ITER's science division, says that information from its plasmas should be useful to ITER.

Delays and using rare isotope deuterium

The reactor took far longer than anticipated to complete—more than 15 years, according to Although it was set to launch in 2016, it encountered numerous difficulties. Along with dealing with procurement issues, it needed to be redesigned in order to recover from the March 2011 Tohoku earthquake. Then, during testing in March 2021, a serious issue arose. A short circuit in the cable of one of the superconducting magnetic coils damaged the electrical connections and resulted in a helium leak that might have impacted the cooling systems.

At that moment, the circuit's current was not very deep. "If the current had been higher, it could have been much worse," QST project manager Hiroshi Shirai stated. "We were fortunate." It took the JT-60SA team 2.5 years to repair the insulation in over 100 electrical connections. The incident also increased the ITER engineers' prudence when it came to coil testing.

The incident happened when the circuit's current was at its lowest. The QST project manager, Hiroshi Shirai, stated that "severe damage to the coil could have occurred if the current had been higher." "We were in luck." It took the JT-60SA team 2.5 years to rework the insulation in over 100 electrical connections for safety. The mishap has also forced ITER engineers to schedule more meticulous testing of their coils.

The disadvantage of JT-60SA is that it will only use hydrogen and its isotope deuterium—rather than tritium, which is a more potent but also more expensive, rare, and radioactive form of hydrogen. Since tritium is the preferred fuel for generating energy, deuterium-tritium will be used by ITER starting in 2035.

Additionally, Japan plans to construct DEMO by 2050, a power plant that would serve as a link between the commercialization of fusion energy and JT-60SA and ITER research. Shirai expressed his happiness at the entry of new, privately funded approaches to fusion energy. He declared that he is open to collaborating with people who have fresh ideas. Shirai remarked, "It's wonderful that more people are in this area."

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