Speaker
Description
Electron cyclotron (EC) radiation plays a critical role in the control of magnetohydrodynamic (MHD) instabilities. Therefore, high optical performance is demanded of EC antennas/launchers [1] in order to achieve effective instability suppression [2,3].
(Figure can be found in the attached abstract)
Figure 1: Schematic representation of thermal disturbances on ray paths (black arrows) as a result of mirror surface (gold) and support backplate (grey) deformation. (I) no thermal disturbance, (II) thermal disturbance from external heat sources (e.g. conduction, cooling channel convection), (III) thermal disturbance from local ray heating.
Current analysis on EC launcher optical components is predominantly focused on structural integrity [4,5]. However, deviations in optical performance due to thermal effects (Fig.1) are not extensively studied in literature, despite high operating temperatures and extremely high beam power densities.
In this work we develop a method to quantify the effect of thermal disturbances on optical performance indicators of megawatt EC optical systems, via a Ray Heated (RH) Structural Thermal Optical Performance (STOP) model[6]. The method couples the thermal domain to the structural domain via thermal expansion. The deformed surface is used in ray-tracing analysis, allowing for optical performance and ray thermal load evaluation of the deformed optical system. We demonstrate the necessity of this modelling approach on a simplified model of the ITER upper launcher.
The results of the case study show significant median ray deviation of 0.23◦ with respect to an undeformed reference beam. In addition, we observe that the beam intensity distribution in the focal plane becomes non-Gaussian with an increased beam width, potentially resulting in a broadening of the power deposition profile.
References
[1] Henderson, M. A., et al. Nuclear fusion 48.5 054013 (2008)
[2] Brand, van den, H. et al. Plasma Physics and Controlled Fusion 54(9) 094003 (2012)
[3] Slief, J.H. et al. Nuclear Fusion 63 026029 (2023)
[4] Vagnoni, M. et al. Fusion Engineering and Design 136 766-770 (2018)
[5] Silva, P. S. et al. Fusion Engineering and Design 146 618-621 (2019)
[6] Johnston, J.D. et al. Optical, Infrared, and Millimeter Space Telescopes. 5487 600-610 (2004)
