Design and analysis of the upper EC launcher for ITER:
Windows and main structural components.

R. Heidinger^1a, I. Danilov^1a, G. Dammertz^1b, U. Fischer^1c, G. Hailfinger^1c,
K. Kleefeldt², A. Meier^1a, E. Stratmanns^1c, M. Thumm^1b,3, A.G.A. Verhoeven⁴

¹ Forschungszentrum Karlsruhe, Association FZK-Euratom,
(a) Institute for Materials Research I, (b) Inst. for Pulsed Power and Microwave Technology, (c) Institute for Reactor Safety, D-76021 Karlsruhe, Germany

² Pfinzstraße 46, D-76689 Karlsdorf-Neuthard, Germany

³ University Karlsruhe, Institute of High-Frequency Techniques and Electronics,

D- 76128 Karlsruhe, Germany

⁴ FOM Institute for Plasma Physics “Rijnhuizen”, Association EURATOM-FOM,

Nieuwegein, The Netherlands

The upper port plug for the EC wave launching system on ITER, which is under development by a working group from various EURATOM associations, is designed for neoclassical tearing mode (NTM) suppression at the q=3/2 and q=2/1 magnetic surfaces. The required variation of the launching angles is based on remote steering optics. The major milestones of the projected design, mock-up testing and component procurement tasks will be summarized.

An important component is the torus window, which serves as a primary tritium confinement and vacuum boundary. The design of the single-disk window proposed by JAERI for the equatorial port is adapted to the ex-vessel space requirements in the upper launcher. The window material will be CVD diamond for which two different brazing methods (Al- and Ag/Cu braze) are considered. The reactive braze ("Ag/Cu") was used in the output window of the long pulse W7-X gyrotron prototype operated at 140 GHz at 540 kW,940 s and 890 kW, 180 s. This brazing process allows to join Cu cuffs to the diamond window faces with the further option of a very compact double disk structure. The Al-braze was used to join Inconel cuffs for the fabrication of a torus window demonstrator at 170 GHz based on a neutron irradiated CVD diamond disk previously exposed to a fluence of 0.9·10²¹ n/m² (E>0.1 MeV). Radiation induced reduction of thermal conductivity was found to be partially recovered by thermal annealing at the brazing temperatures of 600 – 650°C. A neutronics analysis has been conducted to investigate the streaming of fast neutrons in the ECRH waveguide channels with the objective to assess the neutron fluence at the windows for the different types of waveguide channels. Special attention is given to straight waveguides as they facilitate both the design and the maintenance of the ECRH system by avoiding mitre bends.

The design of the mm-wave system is intricately connected to major structural components of the launcher such as the blanket shield module and port plug frame (‘main structure’). A modified geometry for the main structure allows the integration of a twisted 4x2 arrangement of mm-wave waveguides, which is the actual reference model developed by FOM Rijnhuizen. The proposed thickness reduction in the side walls is analysed with respect to launcher deflections. Available data for loads occurring during a VDE Cat III event were taken for an approximate evaluation of a worst case scenario. The largest deflection is found in toroidal direction and amounts to about 8 mm. The proposed attachment scheme for the blanket shield module and the cooling system allows axial access to the in-vessel components of the plug. Therefore lateral openings in the plug structure are not necessarily required for maintenance but considered as an option.