The ITER limiter support system with controlled position of the plasma facing modules

Two ITER limiters, located in two diametrically opposite equatorial ports, perform the specific functions of defining the plasma boundary and protecting other regions of the first wall and antennas from direct contact with the plasma during start-up and ramp-down. The considerable thermal load in these phases (H.D. Pacher, G.W. Pacher, ITER Start-up Limiter Power Loads, INRS Energie et Matériaux, Varennes, Qué., Canada, Report No. NRG-EM-00-676, February, 2001), and the expected high loads during abnormal events, call for a design using a special movable and separable part of the limiter assembly, comprising high-heat-flux components (the limiter module) that require very accurate alignment to the field contour in order to reduce the heat load peaking. Additionally, the design should allow relatively simple remote replacement and refurbishment of the module. Furthermore, uncertainties on the optimum plasma configuration require that the plasma-facing surface can be adjusted to match different plasma scenarios. An engineering design of the limiter port plug with a remotely controlled mechanical supporting and alignment system has been developed to meet all the requirements, providing safe and reliable operation with good margins. The conceptual design of 1998 with its engineering design of 2001 is considered as the current reference for ITER. The paper describes the design and layout of the system and its main components, the principles of operating and assembly.