Preliminary design of the ITER ECH upper launcher

The design of the ITER electron cyclotron launchers recently reached the preliminary design level -the last major step before design finalization. The ITER ECH system contains 24 installed gyrotrons providing a maximum ECH injected power of 20 MW through transmission lines towards the tokamak. There are two EC launcher types both using a front steering mirror; one Equatorial Launcher for plasma heating and four Upper Launchers (UL) for plasma mode stabilization (neoclassical tearing modes and the sawtooth instability). A wide steering angle of the ULs allows to focus on magnetic islands which are expected on the rational magnetic flux surfaces q = 1 (sawtooth instability), q = 3/2 and q = 2 (NTMs). In this paper the preliminary design of the ITER ECH UL is presented, which includes the optical system and the port plug structural components. Highlights of the design include the torus CVD-diamond windows, the frictionless, front steering mechanism and the plasma facing blanket shield module. Numerical simulations as well as prototype tests are used to verify the design.