Structural Thermal Optical Performance analysis of high-power electron cyclotron mirrors

The injection of high-power electron cyclotron (EC) waves is an important actuator for locally energising the plasma in magnetic fusion devices. The injection of these multiple megawatts of EC beams provides a crucial method to precisely deposit the beam power at a desired location inside the plasma, enabling the control of magnetohydrodynamic (MHD) instabilities. However, the effect of thermal deformations of the optical components used to direct the EC beams to their target is still underexplored. To fill this gap, this work presents a test framework for linking thermally induced deformations to optical performance indicators, via a Ray Heated (RH) Structural Thermal Optical Performance (STOP) simulation structure. The applicability of this test framework is demonstrated on a former design of the first mirror of the ITER Upper Launcher (UL) and on a Defeatured Multi-Mirror (DMM) setup based on the UL mirror assembly. The results of the complete RH-STOP modelling approach show an average injection angle error of 0.07° and 0.14° for the old LM1 and DMM case studies, respectively. In addition, the DMM’s focal point is changed to a focal ring with a rough diameter of 3 cm . The results show that the optical performance indicators of a high-power EC system can be significantly affected by both global and local thermal deformation. Moreover, the test framework itself aids in the localisation of the main sources of optical misalignment.