P. Spaeh

Preliminary design of the ITER ECH upper launcher

The design of the ITER electron cyclotron launchers recently reached the preliminary design level -the last major step before design finalization. The ITER ECH system contains 24 installed gyrotrons providing a maximum ECH injected power of 20 MW through transmission lines towards the tokamak. There are two EC launcher types both using a front steering mirror; one Equatorial Launcher for plasma heating and four Upper Launchers (UL) for plasma mode stabilization (neoclassical tearing modes and the sawtooth instability). A wide steering angle of the ULs allows to focus on magnetic islands which are expected on the rational magnetic flux surfaces q = 1 (sawtooth instability), q = 3/2 and q = 2 (NTMs).

Cooling design and analysis of the ITER EC Upper launcher

ITER will be equipped with four EC (Electron Cyclotron) upper launchers of 8 MW microwave power each with the aim to counteract plasma instabilities during operation. The launcher antennas will be installed into four upper ports of the ITER vacuum vessel. All in-vessel microwave components of an EC antenna, comprising several sets of mirrors and waveguides are mounted into so-called upper port plugs. These are basically hollow casks which fit into the ports as cantilevered built-in components, forming thus integrated systems which guarantee optimum performance and simplify assembly and maintenance.

The ITER ECH & CD Upper Launcher: Steps towards final design of the first confinement system

The ITER Electron Cyclotron Heating and Current Drive (ECH&CD) Upper Launcher, whose preliminary design was approved in 2009, is on its way towards the final design. The design work is being done by a consortium of several European research institutes in tight collaboration with F4E. The main focus is the finalization of the design of all components for the First Confinement System (FCS), which forms the vacuum and Tritium barrier. The FCS comprises structural components as well as the external waveguide components in the port cell. Structural components of the FCS include the flange seal, backend frame and closure plate. The external waveguide components include the isolation valve, CVD diamond windows, miter bends and straight waveguides. Because finalizing of the design of these components is directly influenced by the layout of many in-vessel components, the design work includes also further development of the entire launcher. This paper summarizes the most recent status of the design work on the structural components of the launcher FCS, which are the support flange, the socket, the closure plate and feed-throughs for waveguides and cooling pipes. The design work includes the engineering layout of these components in accordance with system requirements, load specifications and Quality and Safety classification. An outline of the overall design of the launcher will be presented. The design progress was based on a set of related analyses, of which particular results are given. Also the integration of the associated mm-wave components, assembly strategies, neutronic aspects and the design of the shielding components will be described.

The ITER EC H&CD upper launcher: Methodology in the FEM analyses of the diamond window unit subject to seismic and baking loads

The ITER electron cyclotron upper launcher (EC UL) is used to direct high power microwave beams generated by the gyrotrons into the plasma for magneto-hydrodynamic (MHD) control and heating and current drive (H&CD) applications. The UL consists of an assembly of ex-vessel waveguides (WGs) and an in-vessel port plug. The diamond window units form vacuum and tritium confinement boundaries between the torus volume and the transmission lines (TLs) which guide beams between 1 and 2 MW from the gyrotrons to the launcher.

Design and testing of the ECH upper port plug for ITER

Four ECH Upper Port Plugs are foreseen at ITER for counteracting plasma instabilities based on the injection of up to 20 MW mm-wave power at 170 GHz into the plasma. The required targeting of flux surfaces will be achieved by angular steering in the poloidal direction. The paper describes the main components of the mm-wave and structural system for the current reference design of the extended physics launcher (EPL). The mm-wave system is formed by waveguide and quasi-optical sections with a front steering system driven by a friction-less and backlash-free pneumatic system. The first tritium barrier is formed by a CVD diamond window with an indirect cooling concept that avoids direct water contact to the diamond disk and brazing material. The structure consists of the blanket shield module with the plasma facing first wall panel, the port plug frame, and the internal shield that provides adequate neutron shielding towards the launcher back-end. The key design requirements for the main structure are discussed with respect to efficient baking, to rigidity towards launcher deflection and to extraction of thermal loads. The current status of fabrication studies is presented demonstrating the feasibility of manufacturing routes for complex double wall structures. Testing of major port plug components is described in the context of dedicated test facilities and maintenance requirements.

Plasma disruptions in ITER and the ECH upper port plug design

During ITER operation malfunctions of the control system due to excessively large perturbations and for special configurations can lead to vertical displacement events (VDE), where a vertical plasma movement is followed by a fast or slow plasma current quench. As a result during the plasma breakdown induced eddy and halo currents cause severe loads on the in-vessel components. For the upper port plug (UPP) structures in ITER the upward VDEs with the subsequent fast current quench are the most critical disruptions. The upper port design requires a plug length of about 5 m with a spacing of 10 mm at the first wall to the neighboring panels. One of the major challenges in the port plug design is to remain within the 10 mm gap during the disruption. The presented ECH UPP structural design cycle combines numerical analysis with manufacturing and prototype issues such as complex double wall structures and joining qualities.

Structural integration of the EC wave launcher at the ITER upper port plug

For plasma stabilisation in ITER, a reference design of an electron cyclotron (EC) wave launcher was developed (8 remotely steerable beamlines) and improved by advanced remote and front steering configurations. The key concepts of their structural integration into the port plug environment are presented for assuring efficient neutron and thermal shielding.

Shield components adopted to the ITER ECRH upper launcher

For control of plasma instabilities, especially neoclassical tearing modes, it is foreseen to inject a total of 20 MW mm-wave power at 170 GHz into the ITER plasma, using a front steering version of the upper launcher. The mm-wave components are integrated into the Upper Port Plug structure which accommodates individual shield components. They provide sufficient shielding and give way for the injected mm-wave power. The shield components presented in this paper are arranged by two major groups: The Front Shield, which is installed into the Blanket Shield Module (BSM) and consists of two discrete blocks. The shape of these components is adjusted to the requirements of the mm-wave system with the special goal to minimise arcing effects. The Port Plug main frame houses the Internal Shield, with two sections: A front section with sophisticated openings for the mm-waves and a rear section, which accommodates the mitre bends or mirrors of the mm-wave system.