Advanced Optics for the Remote Steering ITER ECRH Upper Launcher

The optics of the ECRH Upper Launcher in ITER based on the Remote Steering concept needs special attention, since any focussing element in front of the waveguide has combined effects on the range of steering angles achievable and the beam width in the plasma region. The effects are studied in detail for a setup composed by 8 beams per port (three ports), for a spherical and a hyperbolic mirror surface. Gaussian beam analysis is compared to beam pattern calculations with the optical physics code GRASP, in order to verify the validity of gaussian optics approximation. The standard description with simply astigmatic beams, not adequate in more complex systems as the proposed two-mirror set-up, requires approximations, which are compared with the generalized astigmatic beam description. The ohmic losses at the end mirrors and the related localized heating due to the very large power density cause deformations that depends on the design of the cooling circuit. The distortion of the beam shape has been evaluated in a realistic case of mirror cooling with a small-channel system. The quantification of the effect depends on the precise evaluation ohmic losses and their enhancement in the long term due to the surface deterioration.