Design status of ITER ECH upper launcher mirrors

Abstract

The ITER ECH upper launcher is devoted to directing up to eight 2-MW beams per port plug over half of the plasma cross section. A focusing mirror is used to achieve a very narrow deposition profile to stabilize MHD activity such as the neoclassical tearing modes (NTMs) and the sawtooth oscillation. The beam deposition location is changed via a steering mirror with up to plusmn7 deg (plusmn14 deg beam), which allows access from inside mid radius out to nearly the plasma edge. The steering mechanism uses a frictionless backlash free system to avoid sticking, thus increasing the reliability. A small percentage (<0.5%) of the beam is absorbed upon each reflection from the mirror surface, resulting in absorbed peak power densities ranging from ~2.0 MW/m2 (focusing and steering mirrors) to 3.6 MW/m2 (waveguide mitre bend mirror). The cooling of each mirror has been analysed under ITER conditions using theoretical and finite element modeling (using ANSYS and ANSYSWORKBENCH). The design optimization of the steering mirror has been given considerable attention, aiming at lowering the peak heat load density, while limiting the induced current from the incident changing magnetic field that occurs during a plasma disruption event. The analysis of the mitre bend mirror has been compared to experimental data taken from long pulse (up to 1000 s) , high power (0.3 to 0.8 MW) operation, which has been performed in collaboration with with JAEA, GA, CNR EFDA and CRPP to validate the FE results and to demonstrate that it can withstand high power densities arising from up to 2 MW incident power. This paper will overview the current design status along with the critical design issues for the different in-launcher mirrors.