Progress on the design and manufacturing of the mirrors for the ITER electron cyclotron heating and current drive upper launcher

Four of the 16 ITER upper port plugs will be devoted to electron cyclotron resonance heating (ECRH) in order to control the magneto-hydrodynamic (MHD) instabilities.In order to achieve the stabilisation of the neoclassical tearing modes (NTM) and sawtooth oscillation, a deposition of a very localized, narrow and peaked current density profile over a broad poloidal steering range at the ITER rational surfaces q=1 to q=3/2 and q=2 is required [1]. The quasi-optical configuration consists of eight mm-wave beams entering each of the four upper launchers (UL) through waveguides into the vacuum vessel. Each beam is then directed to the plasma using a serial arrangement of four mirrors, the first set of 2 (mirrors M1 and M2) zigzag the beam line to avoid stray radiation, while the beam-waist locations and beam-shaping properties in the vacuum vessel are defined by the last two mirrors, a static focusing mirror (M3) and a flat poloidally-steerable mirror (M4). These last mirrors (M3 and M4) reflect a group of four beams coming of four individual M1/M2. The plane mirror M4 is steered using a backlash and friction free mechanism that is pneumatically actuated using helium gas. A first prototype of this has been manufactured as a proof of principle and tested for controller design purposes. A second prototype, ITER compatible in terms of the materials used and cooling circuits, will be subject to similar tests throughout the last half of 2009 period.The UL mirrors (static and steerable) absorb heat generated essentially by three sources: the ohmic loss of the RF beam reflected at the mirror surfaces (which is mirror-temperature dependant) and by nuclear (volumetric heating) and thermal radiation (surface heating) coming from the plasma. While the average heat load is calculated to be 2MW beam compatible with reasonable engineering limits, three more important constraints conditioned the actual mirror design, the peak ohmic heat load (the electromagnetic forces generated in vertical disruption events (VDE), and the ITER cooling water requirements. This paper provides an overview of the different upper port-plug mirror designs and stresses several different prototype manufacturing methods for the steering mirror, outlining lessons learned.