Structural design and analysis of an ECRH launcher for JET

The future JET (Joint European Torus) program will be mainly focused on the consolidation of the physics basis of the main ITER scenarios. This gives a strong motivation for examining the feasibility of the construction and implementation of an ECRH (Electron Cyclotron Resonance Heating) system in JET for an intensive exploitation before the start of ITER. To advance this feasibility study towards the approval of the project, collaboration between the E4J (ECRH for JET) project team and the KIT (Karlsruhe Institute of Technology) design team of the ITER ECH Port Plug was decided. The aim of this collaboration was to raise the principal design requirements and to establish a rough design of the main components of an E4J system. This paper presents the conceptual design of the E4J launcher structure. The mechanical structure of the port plug was designed as an integral system to be placed in one of the equatorial ports of JET. These ports are characterized by a very complex shape, which is caused by the available interspaces between the field coils. The launcher is designed to be mounted into the port as a completely pre-assembled unit. The design goal of an integrated system demands a plug-geometry with contracting cross-section from the rear towards the plasma facing side. Thus a casing with a combined structure, whose profile changes from a cylindrical shape in the rear to a rectangular cross-section in the front area, was established. Also the Tritium barrier with individual feed throughs for supplying lines was designed. The casing serves as mechanical support for the cantilevered port plug arrangement. Due to the skewed position of the ECRH-waveguides, sophisticated transition fits and individual studs for proper support of the waveguides were attached. The remote handling capability of particular components was considered to enable maintenance and repair. The feasibility of the design was verified by several structural FEM analyses. The mm-wave system inside the launcher features four sets of mirrors, namely the twelve focusing mirrors, two poloidal steering mirrors, two toroidal steering mirrors and one fixed mirror. All these mirrors must be mounted precisely and securely to the plug structure, thus the mirrors, their steering drives and the mechanical support were designed and analyzed individually.