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ENEA - Fusion division

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Vacuum and Surfaces Laboratory: High-vacuum furnaces

Joining: consolidated know-how

FTU radiofrequency window in Ti//AlFTU radiofrequency window in Ti//Al
The laboratory has developed joining techniques by vacuum and diffusion brazing, which can be implemented in a wide range of joining between metals (steel, copper, molybdenum, tungsten, titanium, etc.) and/or other materials, such as ceramics and composites (graphite, graphite fibre composites, silicon carbide composites).

These techniques have been implemented in fabricating components of the FTU machine, for example, the Radiofrequency Windows with brazing in Ti//Al (see right figure).

ITER divertor prototype in CFC/molybdenumITER divertor prototype in CFC/molybdenum

Another application of CFC/molybdenum joining was for the prototype of the ITER divertor (see left figure).



HRP - Hot Radial Pressing (HRP): a new diffusion welding technique

HRP apparatus (furnace and vacuum system)HRP apparatus (furnace and vacuum system)

This technique (ENEA-CSM patent) for complex, hot, solid-state, simultaneous diffusion welding of co-axial objects is an alternative method to the isostatic-type process (hot isostatic pressing – HIPing).

It was developed by ENEA in collaboration with the Centro Studi Materiali (CSM) of Castel Romano in order to fabricate components of the ITER device (tokamak) that have to resist high heat fluxes.
In this particular case, the component is a heat exchanger consisting of various copper-alloy tubes. Due to the high heat fluxes the tubes have to be protected by a sacrificial material which can withstand the high temperatures and has good thermal contact with the tube itself.
The materials used are basically tungsten (W) and carbon fibre composites (CFC).

The innovation consists in obtaining the joining by putting the component in a vacuum furnace and then applying internal pressure in the cooling tube channel at the prescribed temperature.
The ranges of temperature (up to 700°C) and pressure (up to 1000 bar) that can be reached are sufficient to produce optimum metallurgical bonding of numerous, even dissimilar and not very soluble, metals.

Results and applications

W//Cu prototype for ITER divertorW//Cu prototype for ITER divertor

Tools used for mounting and constructing of mock-up with tungsten tilesTools used for mounting and constructing
of mock-up with tungsten tiles (like the
prototype for ITER divertor) inside the
HRP apparatus above-described

The success of the collaboration is largely due to the technical expertise available at both CSM and ENEA.
CSM has consolidated competence in the characterisation of materials, in fabricating components by HIPing and, above all, in characterising components that have to stand high pressures.
The ENEA Frascati laboratories, on the other hand, have experience in high vacuum technologies, diffusion welding and brazing techniques.

The results can be summarised as follows: