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

A comparison between finite element modeling and various thermographic non-destructive testing techniques for the quantification of the thermal integrity of macro-brush plasma facing components used in a tokamak

The plasma facing components (PFCs) inside a tokamak are typically exposed to extremely high heat flux of the order of MW/m(2). The brazing quality between the plasma facing materials (PFMs) and the heat sink will determine the structural integrity and hence the effective service life of these PFCs. Suitable non-destructive testing (NDT) techniques for the pre-qualification of these components are thus essential to evaluate their structural integrity at various stages of their service life. Macro-brush type mockups of prototype PFCs with graphite as PFM have been inspected for their brazing quality using different active Infrared (IR)-thermographic NDT techniques. The results obtained from these techniques are compared and discussed. The brazing quality was quantified by establishing a comparison between the experimental results and the results from Finite Element Analysis (FEA). The percentage of contact between the PFM and the substrate was varied in FEA. FEA results when compared with experiments shows that tiles have different amounts of contact with the substrate ranging between 10% and 80%.

Nondestructive test of brazed cooling tubes of prototype bolometer camera housing using active infrared thermography

The active infrared thermography technique is used for assessing the brazing quality of an actively cooled bolometer camera housing developed for steady state superconducting tokamak. The housing is a circular pipe, which has circular tubes vacuum brazed on the periphery. A unique method was adopted to monitor the temperature distribution on the internal surface of the pipe. A stainless steel mirror was placed inside the pipe and the reflected IR radiations were viewed using an IR camera. The heat stimulus was given by passing hot water through the tubes and the temperature distribution was monitored during the transient phase. The thermographs showed a significant nonuniformity in the brazing with a contact area of around 51%. The thermography results were compared with the x-ray radiographs and a good match between the two was observed. Benefits of thermography over x-ray radiography testing are emphasized.