The Japanese fusion reactor JT-60SA has just rendered an invaluable service to ITER.

The largest experimental fusion reactor in Europe, JET (Joint European Thor), located in Oxford, England, paves the way for ITER (International Thermonuclear Experimental Reactor). His last major contribution was made public on February 9, 2022. It was the day chosen by the scientists who run it to officially announce that they have succeeded in creating 59 megajoules of fusion energy within 5 seconds. It may seem small, but it is not. This is an important milestone.

However, JET is not the only experimental fusion reactor whose main task is to test the technological solutions that will become part of ITER; there is another, even more ambitious one. This promising machine is called JT-60SA and is located in Naka, a small town near Tokyo (Japan). At the beginning of last February, we told you about this, because plasma testing will begin at the end of this year.

Construction of this experimental fusion reactor began in January 2013, but not from scratch; he did this by taking as his starting point the JT-60 reactor, its predecessor, a machine that went into operation in 1985 and has lasted more than three decades. reached very important milestones in the field of thermonuclear energy. Assembly of the JT-60SA was completed in early 2020 and plasma testing is likely to provide information that will prove invaluable to ITER and the demonstration facility.

JT-60SA coils successfully cooled down to -268 ºC

At present, European and Japanese engineers, who are engaged in fine-tuning the reactor before plasma tests, are finishing fine-tuning the most important subsystems of this extremely complex machine. All of them are important, but one of the most complex is the magnetic engine, which is responsible for holding and stabilizing the plasma containing the nuclei involved in the fusion. And its main components are superconducting magnets located outside the vacuum chamber, and a superconducting solenoid located in the central hole of the reactor. tokamak.

At ITER, the magnets surrounding the vacuum chamber, when installed, will weigh 10,000 tons and will be made of an alloy of niobium and tin or niobium and titanium, acquires superconductivity when cooled with supercritical helium. On the other hand, the central solenoid of both ITER and JT-60SA is responsible for optimizing the geometry of the plasma, stabilizing it, and also helps to heat it up through a mechanism known as the Joule effect.

In order for the magnets and central solenoid of fusion reactors to become superconductive, they must be cooled to an extremely low temperature. And this is not easy to achieve. Luckily, JT-60SA engineers have just succeeded in a very demanding jet aircraft magnetic motor cooling test. And this is that they managed to cool the coils down to 4.8 kelvin (-268 ºC); central solenoid 17 kelvin (-256 ºC); and finally 18 toroidal field coils and 6 stabilization coils reached -264 ºC. This is a real feat.

This milestone is an important step towards the first plasma tests in the JT-60SA reactor, but it’s not good news just for this Japanese machine; This is also for ITER, because the magnetic motor of the Japanese team has implemented some innovations that are supposedly they get to the reactor which is being built in the French town of Cadarache. However, that’s not all. The JT-60SA engineers went one step further by simultaneously heating the vacuum chamber to 194ºC to remove any contaminants present on its surface.

Cover image: F4E/QST

More information: Fusion for Energy

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