Thin TiCx films with a range from pure Ti to stoichiometric TiC (0 ≤ x ≤ 1) have been deposited on carbon-based materials by dual magnetron sputter deposition. The wetting behaviour of a Cu Ti alloy on TiCx coatings has been characterized using the sessile drop method. For these experiments a contact angle measurement device was constructed and successfully tested. Both, stoichiometric TiC and Ti coatings improve wetting dramatically. In between there was no significant wetting improving effect compared to the uncoated case. Subsequently, TiCx coated C/Cu braze joints have been tested on their ability to withstand mechanical loads and analysed with respect to their fracture behaviour.

Finely dispersed Ti-doped isotropic graphites with 4 at.% Ti have been manufactured using synthetic mesophase pitch 'AR' as raw material. These new materials show a thermal conductivity at room temperature of similar to 200 W/mK and flexural strength close to 100 MPa. Measurement of the total erosion yield by deuterium bombardment at ion energies and sample temperatures for which pure carbon shows maximum values, resulted in a reduction of at least a factor of 4, mainly due to dopant enrichment at the surface caused by preferential erosion of carbon. In addition, ITER relevant thermal shock loads were applied with an energetic electron beam at the JUDITH facility. The results demonstrated a significantly improved performance of Ti-doped graphite compared to pure graphite. Finally, Ti-doped graphite was successfully brazed to a CuCrZr block using a Mo interlayer. These results let assume that Ti-doped graphite can be a promising armour material for divertor plasma-facing components. (C) 2009 Elsevier B.V. All rights reserved.

In Plasma Facing Components (PFCs) for nuclear fusion reactors, the protective material, carbon based or tungsten, has to be joined to the copper alloy heat sink for optimum heat transfer. High temperature vacuum brazing is a possible joining process as long as a proper interlayer is introduced to mitigate the residual stresses due to the mismatch of thermal expansion coefficient (CTE). Pure copper can act as plastic compliant layer, however for carbon based materials a proper structuring of the joining surface is necessary to meet the thermal fatigue lifetime requirements. In this work pure molybdenum and tungsten/copper Metal Matrix Composites (W-wires in Cu-matrix) interlayers have been studied as alternative to pure copper for carbon based protective materials in flat tile configuration. Finite element simulations of the brazing process have been performed to evaluate the expected residual stress reduction near the metal-carbon interface. In fact it has been demonstrated that stiff low CTE interlayers can shift the peak stresses from the weak carbon-metal interface to the strongest metal-metal one. Relevant samples have been manufactured and subjected to preliminary metallographic and thermal shock tests. Results obtained so far are encouraging and active cooled mock-ups are being prepared for high heat flux testing. Research work is in progress as regards monoblock configuration with both Wf/Cu MMC and graded Cu/W plasma sprayed and HIPped layers.

In the frame of the EU project ExtreMat new Ti-doped isotropic graphites and carbon fibre-reinforced carbons (CFCs) with high thermal conductivity and reduced chemical erosion were brazed to a CuCrZr heat-sink to produce flat-tile actively cooled mock-ups (MUs). Brazing was done using a low CTE interlayer to shift the stresses to the metal-metal interface. These MUs were exposed to high heat-fluxes in the electron beam facility JUDITH. Screening tests were conducted increasing the heat load stepwise up to 15 MW m(-2), followed by 100 cycles at 15 MW m(-2), subsequent screening up to 20 MW m(-2) and 100 cycles at 20 MW m(-2). All MUs withstood screening at 15 MW m(-2) and most of them survived screening at 20 MW m(-2). Ti-doped CFC MUs showed a significant improvement compared with the undoped reference CFC, surviving several cycles at 20 MW m(-2) on all tiles. One of the Ti-doped graphite MUs withstood 100 cycles at 20 MW m(-2) on one tile, representing a promising result.

A fabrication route based on brazing technology has been developed for the realization of the high heat flux components for the ITER vertical target and Dome-Liner. The divertor vertical target is armoured with carbon fiber reinforced carbon and tungsten in the lower straight part and in the upper curved part, respectively. The armour material is joined to heat sinks made of precipitation hardened copper–chromium–zirconium alloy. The plasma facing units of the dome component are based on a tungsten flat tile design with hypervapotron cooling. An innovative brazing technique based on the addition of carbon fibers to the active brazing alloy, developed by Ansaldo Ricerche for applications in the field of the energy production, has been used for the carbon fiber composite to copper joint to reduce residual stresses. The tungsten–copper joint has been realized by direct casting. A proper brazing thermal cycle has been studied to guarantee the required mechanical properties of the precipitation hardened alloy after brazing.

The divertor design of the ITER fusion machine comprises the joint between CFC composites and the copper alloy heat sink. The main problem of the CFC–Cu joint manufacturing is the large thermal expansion mismatch of the components and the very high contact angle of molten copper on carbon substrates. The aim of this work is to develop a new technique to join CFC composite to pure copper. In order to increase the wettability of CFC by molten copper, the composite surface was modified by direct reaction with group VI transition metals which form a carbide layer and allow a large reduction of the contact angle. A morphological analysis and the mechanical and thermal shock tests were performed to characterize the CFC–Cu joined samples.

After a brief description of the rationale of the material and geometry selection for each carbon armoured plasma facing components, this paper describes the European development of the two basic geometries, namely the monoblock and the hat tile. An overview of the non-destructive inspection techniques specifically developed for these components is also presented.

The ITER divertor design foresees the joint between CFC (carbon fibre reinforced carbon composites) as armor material and a Cu alloy in the heat sink. The purpose of this work is to realize a new joining method between CFC and a pure copper interlayer, required to accommodate the thermal expansion mismatch between CFC and the copper alloy. The joining technique is based on the direct copper casting on CFC surface, which was previously modified by direct reaction with a transition metal of the VI B group. The formation of a carbide layer on CFC surface improves the wettability of molten copper on CFC. The process was also successfully applied to join silicon doped CFC to copper. The paper includes the results of the morphological analysis, the mechanical tests on the joined samples and preliminary thermal fatigue tests.

High heat flux components in International Thermonuclear Experimental Reactor (ITER) are designed as layered structures. In particular, in the heat sink, the assembling of the different parts foresees several joints between C/C composites and Cu alloy. In this paper, two methods to join silicon doped C/C (CFC NS31) to pure copper are described. One method concerns the use of a commercial brazing alloy (70Ti–15Cu–15Ni). The brazing process was optimised and the shear strength of the joined samples resulted to be comparable to the interlaminar shear strength of the C/C composite. The second technique is based on the casting of copper on C/C. The C/C surface was modified by direct reaction with a transition metal. The obtained modified C/C resulted very well wettable by molten copper. The morphological analysis of the C/C–Cu samples was performed.

This task within the EU R&D for ITER had two main objectives: (1) qualification of inspection procedures for plasma facing components (PFC), (2) assessment of the behaviour of calibrated defects under high heat flux (HHF) cyclic loading. The ultimate goal of this work was to demonstrate that the reliable identification of fatal defects by the chosen non-destructive testing (NDT) methods can be achieved. This R&D was carried out according to the following steps: (1) manufacture of a divertor vertical target (VT) prototype with artificial calibrated defects; (2) blind non-destructive round robin test of the prototype; (3) HHF test in FE200 electron beam (EB) facility; (4) post-fatigue blind non-destructive round robin test; (5) destructive examination. The general final conclusion was that the NDT techniques can reliably detect and locate defects having dimensions well below those, which could impair the thermal fatigue lifetime.

This paper summarises the European R&D efforts for the manufacture of shield modules and divertor cassettes for the International Thermonuclear Experimental Reactor (ITER), including their plasma facing components. The various development steps are described as they had to be taken to resolve the fabrication issues, and to keep track with the evolving design requirements and solutions. For all components, the manufacturing feasibility has been demonstrated on prototype scale which puts Europe in the position to start the procurement as soon as the decision about ITER construction is taken. The time period remaining until then is used to optimise the fabrication processes and to develop more cost effective alternatives.

This paper summarises the main activities carried out by the EU Home Team to develop suitable solutions for the ITER high heat flux components, namely the divertor, the baffle and the limiter. The available results demonstrate that the EU have the capability to manufacture high heat flux components with carbon fibre reinforced carbon, tungsten and beryllium armours which all exceed the ITER design requirements.

After an extensive R&D activity, a medium-scale divertor vertical target prototype has been manufactured by the EU Home Team. This component contains all the main features of the corresponding ITER divertor design and consists of two units with one cooling channel each, assembled together and having an overall length and width of about 600 and 50 mm, respectively. The upper part of the prototype has a tungsten macro-brush armour, whereas the lower part is covered by CFC monoblocks. A number of joining techniques were required to manufacture this component as well as an appreciable effort in the development of suitable non-destructive testing methods. The component was high heat flux tested in FE200 electron beam facility at Le Creusot, France. It endured 100 cycles at 5 MW/m2, 1000 cycles at 10 MW/m2 and more then 1000 cycles at 15–20 MW/m2. The final critical heat flux test reached a value in excess of 30 MW/m2.

Four series of plasma sprayed actively cooled mock-ups have been evaluated by infrared measurements and heat flux testing. Infrared characterization showed heat transfer capability of the plasma sprayed layer bonded to the substrate. Even if the thermal conductivity of the B4C plasma sprayed coating is only 5% of the bulk material, the coating can easily survive 1000 cycles at 7.5 MW/m2 if the thickness is less than 150 μm. Thick tungsten coatings (3–5 mm) were more fragile, depending on the plasma spray technology. The highest heat flux acceptable for 1000 cycles is 4 MW/m2 with a vacuum plasma spray coating and a Ni–Al–Si–W precoating, accounting for a reduction in the thermal conductivity by a factor of 3.

The dummy armour prototypes are identical to the reference components in terms of geometry, cooling circuit and material except for the armour material, which is replaced by an equivalent thickness of copper alloy. The main objectives of the dummy armour prototypes are the demonstration of the overall engineering concept of the Divertor, the integration in a 3° cassette together with components manufactured by the other ITER Home Teams and the successive thermo–hydraulic tests on the whole Divertor module. This paper describes the realization of both the wing and the vertical target dummy armour prototypes focusing on the critical aspects of the fabrication and their impact on a further industrialization of the components.

The extensive EU research and development, on international thermonuclear experimental reactor (ITER) high heat flux (HHF) components aims at the demonstration of prototypes for the divertor and baffle with challenging operating requirements. The recent progress of this development is summarised in the paper, particularly concerning the manufacture and testing of mock-ups and prototypes. The available results demonstrate the feasibility of robust solutions with carbon and tungsten armour.

The divertor "Large Project" was conceived with the aim of demonstrating the feasibility of meeting the lifetime requirements by employing the candidate armor materials of beryllium, tungsten (W) and carbon-fiber-composite (CFC). At the start, there existed only limited experience with constructing water-cooled high heat flux armored components for tokamaks. To this was added the complication posed by the need to use a silver-free joining technique that avoids the transmutation of n-irradiated silver to cadmium. The research project involving the four Home Teams (HTs) has focused on the design, development, manufacture and testing of full-scale Plasma Facing Components (PFCs) suitable for ITER. The task addressed all the issues facing ITER divertor design, such as providing adequate armor erosion lifetime, meeting the required armor-heat sink joint lifetime and heat sink fatigue life, sustaining thermal-hydraulic and electromechanical loads, and seeking to identify the most cost-effective manufacturing options. This paper will report the results of the divertor large project.

This paper describes the European technology programme on high heat flux components for the Next Step fusion reactor with main emphasis on carbon armoured mock-ups. The R&D included the development of high thermal conductivity 3D CFC composites, the manufacturing of monoblock and flat tile components, the development of suitable non-destructive methods and the investigation of the critical heat flux limits.

The main European contribution to the ITER divertor project was the development of the divertor target with severe operating requirements such as peak heat loads of up to 20 MW/m2. This development involving EU laboratories and industry included R&D on armour materials, thermo-hydraulics testing, component manufacture, high heat flux testing, design and manufacture of prototypes for later testing. The 4-year EU R&D effort achieved the demonstration of the feasibility of a robust divertor target design based on carbon and tungsten armour. This EU solution has eventually been adopted for the ITER reference design and could be valid also for other ITER high heat flux components such as limiters or baffles.