Mirrors facing Tokamaks’ Plasma

      Comments Off on Mirrors facing Tokamaks’ Plasma

We recently contributed to the development of thermal diagnostic systems to be placed inside future ITER-like tokamaks, for a demonstrator realised by the CEA-Cadarache (*).

Our team (**) at LAM developed a specific polishing process of Molybdenum large (200mm) and highly convex mirrors,. These mirrors are to be used as front mirrors in the Infra-red imaging periscope designed to constantly monitor the heat of the inner parts of the tore confining the plasma.

Molybdenum mirrors have the properties to be resilient to radiations. Molybdenum is therefore one of the materials candidate to be facing the plasmas inside the tores of future Tokamaks. This exotic material deserves a specific treatment during polishing, as its mechanical properties are different from classical materials used for IR imaging.

(*)   This work was made possible with the funding of the AMIDEX foundation.
(**) Polishing handled by Michel MARCOS

IR image taken with the periscope using one of our Molybdenum front mirrors

One of the five Molybdenum front mirrors, installed inside the tore of the WEST experiment.


More details about the project:
(Abstract out of the proceeding of X. Courtois et al, Symposium On Fusion Technologies, 2018)

The WEST platform aims at testing ITER like W divertor targets in an integrated tokamak environment. To operate long plasma discharge, the IR thermography is required to monitor the main plasma facing components by means of real time surface temperature measurements, while providing essential data for various physics studies.

To monitor the new divertor targets, the WEST IR thermography protection system has been deeply renewed, to match with the new tokamak configuration. It consists of 7 endoscopes located in upper ports viewing the whole lower divertor and the 5 heating devices. Electronics devices and computers allow a real time data processing at a frame rate of 50 Hz, to ensure the protection of the main plasma facing components during plasma discharges by a feedback control of the heating devices injected power, and the data storage of ≈3 Gb/s IR images.

Each endoscope provides 2 views covering 2 divertor sectors of 30° (toroidally) and 1 view of a heating antenna. Each optical line is composed of a tight entrance window followed by a head objective which forms an image transported through the endoscope by a series of 4 optical relays and mirrors, up to a camera objective. Finally, 12 IR cameras specially developed for WEST environment capture the thermographic data, at the wavelength of 3.9 mm, with a 640×512 pixels frame size.