Design of the Cooling System of the Cavity of the European Gyrotron Using Adjoint-Based Topology Optimization Exploiting the Azimuthal Flow Direction

The present study aims to apply adjoint-based topology optimization to optimize the cooling system of the Gyrotron cavity, exploiting the azimuthal flow direction. The layout of the cavity of the MW-class gyrotron is a crucial point for reaching the target performance of the device, in the context of a highly non-homogeneous heat load, peaked at values up to 25 MW/m2. A proper cooling system allows to maintain deformations below the threshold that keep the resonant working conditions, keeping at the same time the stress in the elastic regime. A tailored heat removal capability at a controlled pressure drop is addressed in this study using adjoint-based topology optimization in OpenFOAM, for a cooling configuration that involves the possibility for the subcooled water to flow partially in the azimuthal direction around the cavity. The outcome of the optimization is then compared with a solution obtained with a biogeography-based optimization algorithm, in the past. The results of the optimization show a significant effect on the peak temperature reduction, compared to the non-optimized configuration, but only a relaxation of the constraint on the pressure drop could bring the performance at a level comparable to that of other optimized solutions.