Design of a tunable torus window for ASDEX Upgrade

R. Heidinger ¹⁾, I. Danilov ¹⁾, A. Meier ¹⁾, F. Leuterer ²⁾, D. Wagner ²⁾

¹Forschungszentrum Karlsruhe, Association FZK-Euratom

Institut für Materialforschung I, D-76021 Karlsruhe, Germany

² Max-Planck-Institut für Plasmaphysik, EURATOM Association IPP-Garching,

D-85748 Garching, Germany

The state of the art of output windows for Megawatt gyrotrons relies on edge cooled windows equipped with a single large area CVD diamond disk of resonant thickness. For step-tunable gyrotrons, this concept does not satisfy the required minimum reflection conditions and is therefore replaced by a double disk window design. The paper presents the mechanical design and thermo-mechanical simulation of a double disk window for multi-frequency Electron Cyclotron Heating at ASDEX-U operated at four distinct frequencies at ~ 105 … 140 GHz. For the two intermediate frequencies (around 115 and 125 GHz), the minimum reflection will be achieved by high precision tuning of the distance between the two CVD diamond disks (adjustment tolerances ± 5µm). A small working distance of 4 … 6 mm is realised by single face cooling. Cooling chambers for direct face cooling are prepared by a double ring configuration realised by joining two concentric copper cuffs to the diamond faces using an Ag-based braze. The flow distribution of the pressurised water through the specific cooling structure has been modelled and the temperatures obtained for centre and the edge of the disk. Averaged effective heating transfer coefficients have been obtained as the function of the water consumption to quantify the efficiency of the cooling concept and to couple simulation models. Thermally induced stress and deformation in the window structure have been determined by FEM analysis, they are shown to be compatible with the specified limits.