R. Mitteau

High heat flux testing impact on the Tore Supra toroidal pumped limiter achievement

The toroidal pumped limiter of Tore Supra is made of 576 elementary high heat flux (HHF) cooled plasma-facing components (PFCs) and designed to sustain 10 MW/m/sup 2/ in steady state. One of the main technical difficulties is to ensure a high quality of the bond between the carbon fiber composite armor tile and the water-cooled heat sink due to the high thermal stresses that develop at the bond during operation. Consequently, a HHF facility able to reproduce in service operation of PFCs is required all along the development and manufacturing route. In Europe, the FE200 facility (electron beam, 200 kW, France) operating since 1991, was extensively used for such a development. A first testing campaign in 1995 was devoted to the qualification of this bond: AMC/spl reg/ technology from Plansee GmbH was selected. Afterwards, a second campaign on scale-one elements (1996) allowed an optimization of the element design and series production to be launched. During the mass production, a non-destructive control process - cheaper and faster than HHF testing - based on infrared characterization was routinely operated on 100% of the manufactured elements. Strong variability of the bond quality was observed and a repair process allowing the replacement of deficient tiles was developed. In 2000 and 2001, 2 campaigns of HHF testing were launched to correlate the non-destructive measurements and to optimize and validate the repair process. This was done, in two steps, with success. This yielded moreover interesting information for qualifying both tests across each other and also to analyze the fatigue evolution of the bond. The qualification and the achievement of the Tore Supra limiter has greatly been made possible by such HHF tests, which appears as essential before and during PFC manufacturing.

A Geometrical approach to evaluating the heat flux peaking factor on first wall components

Abstract In magnetic fusion experiments, a simple technique to evaluate the heat flux on first wall components is a key to controlled plasma surface interaction. The heat flux can be characterized by the peaking factor which is the ratio of the peak heat flux to the average heat flux. The peaking factor can be calculated exactly using simple derivations and standard software tools. This analysis is applied to an Iter class experiment for plasma-wall contact during start up phases at 15xa0MW, in idealised, realistic and misaligned situations. Even though the peaking factors are usually above 10, the peak heat load on the wall remains moderate at a few MW/m2.

Tungsten/Copper Functionally Graded Materials: Possible Applications and Processing through the Powder Metallurgy Route

Processing of W-Cu graded materials from attritor-milled W-CuO mixtures is described. The powder reduction steps are investigated by TG and XRD analyses and by microstructural observations (SEM, TEM). Sintering of reduced powder with different compositions is analysed by dilatometry. Sintering behaviour of the graded component processed by co-compaction of a 10/20/30wt%Cu multi-layer material is briefly discussed. Liquid Cu migration is observed and smoothes the composition gradient. Perspectives to control this migration are discussed.

Control of the Composition Profile of Tungsten-Copper Functionally Graded Materials for Fusion Technology Application

This work aims to process W-Cu FGM for fusion material applications, in particular plasma facing components (PFC). Currently, PFCs are made by multi-material assembly and rely on tungsten armour tile (high heat flux side) which needs to be cooled by the attachment to a heat sink (Cu-alloys). The interfaces in multi-material assembly are unfavourable for the application (high working temperature, thermal fatigue). The use of FGM can be a new promising way. The aim of this study is to analyze the effect of a composition/grain size variation on the liquid phase migration during liquid phase sintering of FGM, in order to control the final composition profile. Bi-layer materials are processed by powder metallurgy route. W-Cu compositions with 10 and 20wt%Cu and with different W-particle sizes are processed starting with attritor-milled W-CuO powder mixtures which are reduced at 350°C. Analysis of copper liquid phase migration for different composition/grain size associations indicates that the phenomenon is driven by differential sinterability in the gradient. The copper liquid migration depends on the differences in sinterability, on the available liquid and open porosity in the structure beyond the melting point of copper. From these analyses, a way to control the gradient profile of W-Cu structure can be proposed.