Structural system of the ECH upper port plug for ITER

Full text: Four positions of the ITER upper port configuration are foreseen to accommodate the EC wave launching system for inducing localised current drive (CD) at the magnetic island locations. Its main objective is to stabilise the Neoclassical Tearing Modes (NTM) which is achieved by steering the EC beams over a range of plasma areas (typically ρp of 0.64 - 0.9) with a CD efficiency sufficient to stabilise 3/2 and 2/1 NTMs for the reference scenario 2, but also for the hybrid scenario (3) and for the low-q operation (scenario 5). It is further desirable that the Upper Launchers can be used to access the q=1 region of plasmas with positive shear (function potentially shared with the equatorial launcher) to provide control of the sawtooth period and amplitude. In present reference design, the 'Extended Performance front steering Launcher' or EPL, this functionality is achieved with a steering range covering ρp of 0.4 - 0.9. The development of the structural system of the EPL is presented in this paper. The mm-wave components are integrated into the upper port plug structure which consists of two separate units, namely the blanket shield module (BSM) forming the plasma-facing component and the launcher main structure, which are connected with a bolted flange allowing axial access to the plug internals for maintenance and disassembly. The development of the structural system covers the adaptation of the shielding and cooling configuration of the BSM and of the internal neutron shield in the main structure to comply with the mm-wave beam line design. The evolving manufacturing concepts striving for communality with diagnostics plugs has led to the current slim wall design for the main structure. It is characterised by a passively cooled single wall section forming the central part intermediate to the actively cooled double wall sections at the front and back end. With a removable cover it allows vertical access to the internals. The baking concept is analysed for this design proving that the baking temperature at the port plug does not fall below 200 deg. C. (author)