A. Vaccaro

Objectives, physics requirements and conceptual design of an ECRH system for JET

A study has been conducted to evaluate the feasibility of installing an electron cyclotron resonance heating (ECRH) and current drive system on the JET tokamak. The main functions of this system would be electron heating, sawtooth control, neoclassical tearing mode control to access high beta regimes and current profile control to access and maintain advanced plasma scenarios. This paper presents an overview of the studies performed in this framework by an EU-Russia project team. The motivations for this major upgrade of the JET heating systems and the required functions are discussed. The main results of the study are summarized. The usefulness of a 10 MW level EC system for JET is definitely confirmed by the physics studies. Neither feasibility issues nor strong limitations for any of the functions envisaged have been found. This has led to a preliminary conceptual design of the system.

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).

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.

Collector Loading of the 2-MW, 170-GHz Gyrotron for ITER in Case of Beam Power Modulation

To control different types of magnetohydrodynamic instabilities in the fusion experiment ITER, various amplitude modulation scenarios for the gyrotrons of the electron cyclotron system are required. This paper focuses on the impact of different modulation scenarios on the power loading on the collector wall of the 2-MW EU gyrotron. In addition, first investigations of the transient thermal behavior of the collector structure are performed.

Structural design of the iter ec upper launcher

To counteract plasma instabilities, Electron Cyclotron launchers with a total Millimeter-wave power of 20 MW are installed into four of the ITER Upper Ports. Each Mm-wave-system consists of eight transmission lines; a quasi-optical focusing mirror system and two steerable front mirrors to be capable of injecting the beams over the range plasma instabilities are susceptible to occur. The Mm-wave-systems are mounted into a stainless steel cask which has to meet the demands on precise alignment; high-performance cooling for substantial nuclear heat loads; mechanical strength to sustain plasma disruptions and proper nuclear shielding. A structural system of two main components was investigated on a conceptual level. It is composed of the Blanket Shield Module (BSM) and the launcher mainframe. A removable flange connection between the BSM and the main frame provides access to the launcher internals. The entire system is attached to the standard ITER Port interface. Appropriate remote handling capability is also considered. For the BSM and the front segment of the main frame a rigid double wall structure with meandering rectangular cooling channels was designed. The rear part of the main frame consists of a single wall element with individual openings to simplify maintenance access. A shielding concept which serves also as an optical bench for the Millimeter-wave system was developed. Analyses regarding mechanical strength, thermo-hydraulic behavior, baking capability and shielding efficiency were performed. To investigate industrial manufacturing routes, several prototypes of characteristic sections of the BSM and the main frame were manufactured. They are under study at the Launcher Handling Test facility (LHT) at FZK, which is able to simulate different ITER operating conditions. Extensive test series were performed to validate underlying analysis related to temperature distribution, pressure drop within the cooling paths and removal of applied heat loads.

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.

Impact of gyrotron power modulation on the collector of the 2 MW, 170 GHZ gyrotron for ITER

Summary form only given. In ITER it is foreseen to control different types of MHD instabilities by means of modulated Electron Cyclotron Current Drive (ECCD) with modulation frequencies up to 5 kHz. This has direct consequences for the EC system of ITER, since both the gyrotons and power supplies have to be capable of modulated operation. Since the electron gun of the 2 MW EU gyrotron is a diode type gun and the gyrotron is equipped with a depressed collector, two modulation scenarios were investigated: • Modulation with the body power supply (BPS): In this case the gyrotron output power will be controlled by the voltage of the BPS. The required change of the BPS voltage will reduce both the output power and efficiency of the gyrotron but will also reduce the deceleration voltage of the depressed collector. This fact, together with the reduced efficiency, will increase the power load on the collector wall significantly. • Modulation with the main power supply (MPS): In this case the output power is controlled by a reduction of the voltage provided by the MPS. Since the deceleration voltage of the depressed collector will not be affected, the power load on the collector is only influenced by the reduced interaction efficiency.

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.

Aufbau eines Versuchsstandes für den ECH Upper Launcher in ITER - Schlussbericht zum Vorhaben 3FUS0010 (KIT Scientific Reports ; 7694)

Um Plasmainstabilitaten zu begegnen, werden in vier der oberen Ports im ITER Vakuumgefas Electron Cyclotron Launcher installiert. Diese bestehen im Wesentlichen aus einer trapezformigen Stahlkonstruktion, welche die Mikrowellenkomponenten (im Wesentlichen Spiegel und Wellenleiter) beherbergt. Bei der Konstruktion eines solchen Launchers mussen als wesentliche Vorgaben die mechanische Festigkeit, die ausreichende Kuhlung des Systems und wirksame Abschirmung gegen Neutronen berucksichtigt werden.