On 22 April 2025, the final components of the Edge Thomson Scattering (TS) diagnostics arrived at the JT-60SA facility in Naka, Japan, marking the start of the system’s installation.
The Edge TS has been a truly international effort, as part of the Europe-Japan collaboration in the fusion experiment JT-60SA, jointly managed by F4E and QST. Following years of design, procurement, assembly, and testing in Italy (Consorzio RFX and CNR, Padua), Romania (ICSI, Râmnicu Vâlcea) and Japan, the project has entered its final stage.
Thomson Scattering is a key diagnostic tool for magnetic confinement fusion devices, measuring plasma electron temperature and density by analysing Doppler-broadened light from a high-powered laser beam scattered by plasma electrons. JT-60SA will feature two subsystems currently being installed: the core TS, developed in Japan, and the edge TS, built primarily in Europe. The core TS covers 46 radial points from 2.6 m to 3.73 m, while the edge TS spans 49 points between 3.7 m and 4.17 m of the major radius. Spacing narrows from 25 mm in the core to just 5.5 mm at the edge, enabling unprecedented detail in resolving pedestal profiles. Operating at 50 Hz (core) and 100 Hz (edge), the system offers exceptional capability for plasma control.
The delivery of the components of the Edge Thomson Scattering diagnostics to the JT-60SA site in Naka, Ibaraki has been completed on 22nd April 2025. Credit: QST
The coming months will see the installation progress from positioning the ex-vessel support structure to mounting the collection optics and aligning the light transmission system, built with over 1,100 km of fibre optics, which will transfer signals to the analysis systems. All the back-end systems—polychromators, detectors, electronics, and the laser source—are already in place.
Final calibration will include spatial alignment inside the vessel and absolute calibration using Raman scattering in nitrogen gas at room temperature. Once complete, JT-60SA will have one of the most advanced plasma diagnostics set in the world.
