New diagnostic systems in progress to upgrade JT-60SA

The fusion reactor JT-60SA, built by Europe and Japan, was switched on for the first time in 2023. The experiment went on to achieve the record for the largest plasma volume ever and, shortly after, it was turned off. At present, preparations are underway for a powerful return in 2026. The machine will come back with an improved performance. The teams in Naka are working against the clock to install all the new components foreseen in the plan, such as the divertor cryopump, the pellet launching system or additional heating systems.

With the next plasma shots at JT-60SA, scientists will gain unique insights for the future operation of larger reactors like ITER. But capturing the data from inside is a challenge in itself. To make it possible, JT-60SA will feature a wide set of diagnostic technologies monitoring many different parameters in real time. Fusion for Energy (F4E) is providing nine of these advanced instruments for the current upgrade stage, in collaboration with EUROfusion laboratories.

One of them is the Edge Thomson Scattering (ETS), a system to measure the temperature and density of electrons in the outer region of the plasma. In essence, the ETS works by firing a laser into the plasma. Its light is scattered by fast-moving electrons and then re-collected through optical systems. From the way the light is spread, scientists can calculate how hot and dense the plasma edge is. This, in turn, helps them analyse the confinement of the plasma and control its stability.

F4E and EUROfusion worked with Consorzio RFX (Italy) and ICSI (Romania) to design, test and manufacture the ETS. The components arrived onsite in Naka last April and were ready for installation. QST and its assembly supplier started with the support structure, fitting it diagonally into one of the tokamak's lower ports. Carlos Ortiz, F4E Technical Officer, followed the process closely alongside his Japanese colleagues. "We managed to hoist a 10-tonne structure into position with millimetric precision. With the ramp and trolley in place, we will be able to insert the optical parts of the system soon," he explains.

Europe is also making headway with the Divertor Vacuum Ultraviolet spectroscopy. This technology will be used to detect and measure impurities in the plasma by analysing the ultraviolet light they emit. F4E collaborated with EUROfusion, Consorzio RFX, ENEA and ICSI to develop and manufacture it. The system will pass its final tests in ENEA (Italy) towards the end of the year and soon after will be shipped to Japan for installation in JT-60SA.

Besides these, F4E is working with its EUROfusion partners to advance the rest of European diagnostics, such as the Tangential Phase Contrast Imaging or the Fast-Ion Loss Detector. "Developing such a range of instruments is bringing us a great chance to grow the European expertise in state-of-the-art diagnostic techniques and put it in practice," asserts Mario Cavinato, F4E Project Manager and coordinator of the EU enhancements. "We're very excited to see them at work in JT-60SA, enabling the safe operation of the experiment and providing a wealth of key data for the fusion community," adds Nandor Hajnal, F4E Technical Officer.