The JT-60SA experimental nuclear fusion reactor is an essential milestone on the road to ITER (International Thermonuclear Experimental Reactor), the huge fusion reactor being built by a European-led international consortium in Cadarache, France. Like the latter, the JT-60SA is a tokamak-type magnetic confinement fusion reactor, but it is not located in Europe, but in Naka, a small town not far from Tokyo, Japan.

Its construction began in January 2013, but it didn’t start from scratch; it took as its starting point the JT-60 reactor, its precursor, a machine that went into service in 1985 and, over more than three decades, achieved very important milestones in the field of fusion energy. Assembly of the JT-60SA was completed in early 2020, and the intention of the scientists involved in commissioning it was to start plasma testing as soon as possible.

Important note: Europe and Japan are working hand in hand on the development and operation of the JT-60SA reactor. This is a joint project, the ultimate aim of which is to carry out experiments capable of providing invaluable knowledge for the success of ITER. This is precisely the importance of the Naka machine. Fortunately, so far this collaboration is going according to plan. Witness the new milestone reached by European and Japanese technicians.

The first plasma test on the JT-60SA reactor has been successful, paving the way for the first phase of experimentation.

Over the past few months, the JT-60SA experimental reactor has offered us a number of joys. The latest, and undoubtedly the most important, came at the beginning of August. The engineers working on the development of this machine succeeded in cooling the reactor’s magnetic motor. This was no easy feat, as the temperatures required for the magnets and central solenoid in fusion reactors to reach superconductivity are extremely low.

For the JT-60SA reactor, the operating temperature of the coils is 5.15 Kelvin (-268ºC), that of the central solenoid 17.15 Kelvin (-256ºC) and that of the 18 toroidal field coils and 6 stabilization coils 9.15 Kelvin (-264ºC). The next important step was to start up the reactor for the first plasma test. This crucial test was carried out a few days ago by the engineers operating the reactor and, fortunately, it was successful. Over the next few weeks, they will continue to study the results obtained and carry out further tests, but this first test went off without a hitch. In any case, they will publish their final analysis on December 1.

📢We did it!👐
🇪🇺🤝🇯🇵 have acheived a first Tokamak plasma at
JT-60SA 🌞
We are carefully examing all details 👀🧑‍🔬👩‍🔬
More to be revealed on 1⃣.1⃣2⃣.2⃣0⃣2⃣3⃣ at the inauguration ceremony of the JT-60SA facility 🎉
Stay tuned for more details! #fusionenergy pic.twitter.com/hWkWee3vqw

— Fusion For Energy (@fusionforenergy) October 24, 2023

This milestone opens the door to the first experimental phase of the JT-60SA reactor, which aims to demonstrate that the superconducting magnets responsible for confining the plasma at very high temperatures behave stably when supplied with a very high current. During this phase, researchers will also carry out other fundamental checks, including monitoring the shape of the plasma and analyzing impurities that accumulate in the reactor core.

Generally speaking, the next phase aims to study plasma behavior, which will be very important in determining whether the stabilization strategies that will be implemented as part of ITER are appropriate. When fully operational, the JT-60SA reactor will be able to sustain a plasma of deuterium nuclei for a period of 100 s, using a maximum current of 5.5 MA. ITER will be larger than JT-60SA, which, in theory, will enable it to reduce energy loss in the reactor core and contribute to plasma stabilization.

The fifth experimental phase aims to mitigate the potential risks associated with operating ITER.

The third experimental phase of the Naka fusion reactor will attempt to recreate operating conditions as close as possible to those of ITER in order to accurately predict plasma behavior in the experimental reactor at Cadarache (France). This phase is similar to the previous one, but researchers will now be monitoring very specific parameters that condition plasma behavior, such as its intrinsic rotation or the effects of particle energy on plasma stabilization and confinement.

The fourth phase of experimentation on the JT-60SA reactor is generally aimed at finding the ideal operating parameters for optimizing plasma behavior in real time, minimizing energy loss and resolving impurity transport with guarantees. Finally, the fifth phase aims to mitigate the potential risks associated with operating ITER. If all goes according to plan, EUROfusion will start low-power tests with hydrogen and helium in this last experimental reactor in 2028, and high-power tests in 2032. The JT-60SA reactor will be an invaluable ally, without which ITER would certainly have many more difficulties.

More information: Fusion for Energy

Cover image: © F4E/QST.