Design and Numerical Analyses of the M4 Steering Mirrors for the ITER Electron Cyclotron Heating Upper Launcher

Four electron cyclotron heating upper launchers (ECHULs) will be used at ITER to counteract magnetohydrodynamic plasma instabilities by targeting them with up to 24 MW of mm-wave power at 170 GHz. This mm-wave power is injected through eight ex-vessel (EV) waveguide assemblies for each ECHUL to the in-vessel (IV) waveguides. The mm-wave power exiting the eight IV waveguides inside the ECHUL is reflected by three fixed mirror sets and finally aimed by two independent steering mirrors to specific plasma locations. These two steering mirrors have recently experienced an important redesign in order to deal with the new requirements. This article reports the status of the steering mirrors as well as the fluid dynamic and thermomechanical analyses carried out to validate the design for the normal operation (NO) scenario. The fluid dynamic analyses show that the power dissipated in both steering mirrors due to the mm-wave radiation, nuclear heating, and plasma heat flux can be properly removed with an acceptable mass flow generating admissible pressure drop, temperature rise, and corrosion rate values. The results obtained in the thermomechanical simulation, validated using the American Society of Mechanical Engineers (ASME) code, shows that the steering mirror design is capable of withstanding the expected loads taking place during NO.