Design and Thermal-Structural Analyses of Ancillary Components for the Optical Steering Mirror (M4) for the ITER ECH Upper Launcher

Each of the four ITER Electron Cyclotron Heating Upper Launcher (ECHUL) features eight transmission lines (TLs) that are used to inject 170-GHz microwave power into the plasma at a level of up to 1.31 MW (at the TL diamond window) per line. The millimeter waves are guided through a quasi-optical section consisting of three fixed mirror sets (M1, M2, and M3) and one front steering mirror set (M4), with a steering range of [-7, +7]°. The M4 mirror assembly (upper and lower) will each reflect nearly four Gaussian beams at the correct location in the plasma for suppression of the ${q}\,\,=3$ /2 and ${q}\,\,=2$ /1 NTMs. EPFL-SPC has developed a novel steering mirror assembly (SMA) actuator system, which is based on four pressure-controlled, helium-filled bellows working against six helicoidally machined, preloaded, compressive springs, that rotate around two frictionless flexure pivots. This article will outline the design and thermal-mechanical analysis of such bellows, springs, housing (stator), and the remote-handling compatible support frame.