Preliminary Investigation of Optical-Path-Related Elements in the Port Plug of ITER Core LIDAR Diagnostics

This paper describes the preliminary engineering investigation of the optical labyrinth and the first and second mirror mounts of the ITER core LIDAR diagnostics. The optical labyrinth is in a very sensitive location being close and open to the plasma. Therefore, it has been examined carefully to be able to provide different solutions satisfying the needs of the diagnostics. The present conceptual design considered the covering of the light path, the integration of the labyrinth into the port plug, as well as the shape, color, and material of the labyrinth inner surface. It was absolutely necessary, since the undesirable phenomena of scattered light and sputtered particles reaching the mirroring surface must be handled. Nevertheless, cooling/baking has also been considered, and appropriate solutions have been presented. Regarding the mirror mounts, concepts have been created. It has been identified that the mirrors must be conditioned at a certain temperature; therefore, cooling/baking options were developed. The cooling/baking and, particularly, the neutron absorption functions were detected to be essential for the extension tubes. The development basically focused on the different installation methods of the neutron-shielding plates, which also allow the tubes to be kept in the required temperature range. The result of the development was that a water-steel mixture varied through the length of the extension tubes could provide the maximum neutron shielding. This solution could satisfy the very strict six-orders-of-magnitude neutron absorption required to maintain the postoperation safety. The conceptual engineering design has been supported by the preliminary thermal analysis of the mirror extension tubes.