Qualification and Post-Mortem Characterization of Tungsten Mock-ups Exposed to Cyclic High Heat Flux Loading

High heat flux testing of mock-ups for a full tungsten ITER divertor

The ITER divertor vertical target has to sustain heat fluxes up to 20 MW m−2. The concept developed for this plasma facing component working at steady state is based on carbon fibre composite armour for the lower straight part and tungsten for the curved upper part. The main challenges involved in the use of such components include the removal of the high heat fluxes deposited and mechanically and thermally joining the armour to the metallic heat sink, despite the mismatch in the thermal expansions. Two solutions based on the use of a CuCrZr hardened copper alloy and an active metal casting (AMC®) process were investigated during the ITER EDA phase: the first one called 'flat tile geometry' was mainly developed for the Tore Supra pumped limiter, the second one called 'monoblock geometry' was developed by the EU Participating Team for the ITER project. This paper presents a review of these two solutions and analyses their assets and drawbacks: pressure drop, critical heat flux, surface temperature and expected behaviour during operation, risks during the manufacture, control of the armour defects during the manufacture and at the reception, and the possibility of repairing defective tiles.

https://iopscience.iop.org/article/10.1088/0029-5515/45/6/013/pdf

Technologies for ITER divertor vertical target plasma facing components

The WEST programme: Minimizing technology and operational risks of a full actively cooled tungsten divertor on ITER

The target areas intercept the open field lines at the plasma boundary and are the most heat-loaded zone of the WENDELSTEIN 7-X (W7-X) divertor. The 19 m2 of the target areas, which are formed by 890 water-cooled target elements, are made of CuCrZr heat sinks covered with CFC tiles. Before mass-production, a pre-series stage has been launched to qualify the design and the various steps of the manufacturing route. The purpose is to select the technology to bond the tiles, to qualify the different non-destructive examinations and to better define the relevant acceptance criteria for the serial production.

Applied technologies and inspections for the W7-X pre-series target elements

Among all non-destructive examinations (NDE), active infrared thermography is becoming recognised as a technique available today for improving quality control of many materials and structures involved in heat transfer. The infrared thermography allows to characterise the joint between two materials. In order to increase the defect detection limit of the SATIR test bed, several possibilities have been evaluated. The implementation in 2003 of a microbolometer camera and the improving of the thermosignal process allowed to increase considerably the detection sensitivity of the SATIR facility. The quality, the spatial stability of infrared image and the detection of edge defect have been also improved. The coupling on the same test bed of SATIR method with a lock-in thermography will be assessed in this paper. An improvement of the global reliability is expected by data merging produced by the two thermal excitation sources. This new facility SATIR UPGRADE has been designed for the full non-destructive examination of the high heat flux (HHF) components taking into account these main improvements. These systematic acceptance tests obviously need tools for quality control of critical parts.

Development of an original active thermography method adapted to ITER plasma facing components control

Up-to-date development of actively cooled high heat flux (HHF) plasma facing components (PFC) prototypes only allows reduced margins with regards to the ITER thermal requirements. Additionally, perfect quality cannot be ensured along series manufacturing: the presence of flaws which impair the heat transfer capability of the component, in particular at the interface armour/heat sink appears to be statistically unavoidable. In order to ensure a successful series production, a qualification methodology of actively cooled high heat flux plasma facing components is proposed. Secondly, advanced non-destructive techniques developed for HHF PFC commissioning are detailed with definition of acceptance criteria. Finally, innovative diagnostics for in situ monitoring during plasma operations or tokamak shutdowns are investigated in order to prevent immediate damage (safety monitoring); or evaluate component degradation (health monitoring). This work takes into account the relevance to Tore Supra, and is applied to W7X and ITER Divertor HHF PFC.

J.L. Farjon

Papers

Development of an original active thermography method adapted to ITER plasma facing components control

Qualification, commissioning and in situ monitoring of high heat flux plasma facing components

An operational non-destructive examination technique for ITER Divertor plasma facing components