Conceptual design of optical path related elements in the port plug of ITER core lidar diagnostic

The present paper describes the engineering conceptual design of the optical labyrinth and the first and second mirror mounts of the ITER core LIDAR diagnostics. The optical labyrinth, being in a very sensitive location close and open to the plasma, has been examined carefully to be able to provide different solutions satisfying the needs of the diagnostics. Therefore the 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 to be able to handle the undesirable phenomena of scattered light and sputtered particles reaching the mirroring surface. Nevertheless, cooling/ baking has also been considered and appropriate solutions 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 especially 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 in a way to be also able to provide the tubes 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, hence satisfying the very strict requirement of 6 orders of magnitude neutron absorption required to maintain the post operation safety. The conceptual engineering design has been supported by preliminary thermal analysis of the mirror extension tubes.