Just a few centimetres away from the hot plasma in ITER is the blanket
Artistic representation of the in-vessel lighting system. To illuminate the vacuum vessel, laser light is injected inside the vacuum vessel through the existing system of mirrors, making it possible to capture images of the first wall between plasma pulses. The inset on the bottom right shows the optical boards of a sub-system of the in-vessel lighting diagnostic, featuring cameras, movable mirrors and laser optical heads.
The spatial resolution of the images depends on the distance from the camera to the object, but it will be on the order of a few millimetres, which is enough to detail potential wall damage such as melt features. Some of the views overlap and software can be used to combine the overlapped images to get more detail. When the views are alternated and a picture is taken from each of the optical paths, the operation produces up to 20 full images of the torus wall.
The new in-vessel lighting system has the advantage of being fast and readily deployed, capable of providing a first indication of any damage to the ITER first wall. Left: Image taken inside of the JET tokamak showing a proxy of melt damage inside of ITER. Right: A simulated image, showing the quality expected from ITER's new illumination diagnostic (taken from a distance of 7 metres).