THERMAL RESPONSE AND FATIGUE BEHAVIOUR OF BRAZED CFC/TZM/Mo41Re-DIVERTOR MOCK-UPS UNDER ELECTRON BEAM LOADING

For the divertor of NET/ITER the development of actively cooled components which are able to withstand the high heat loads during normal operation is one of the key issues. TZM heat sinks with CFC armour tiles brazed to the plasma facing side and a Mo41Re cooling tube may provide a solution for such high heat flux components. Manufacturing of the mock-ups is performed in two main steps: in the first step the CFC tiles, 26 × 44.5 × 9 mm 3 , are brazed to a 2 mm thick “interlayer” of TZM by use of a Zr braze. Subsequently these CFC/TZM units are brazed to the TZM heat sink by means of a CuPd alloy with a lower melting temperature than the Zr braze. The interlayer serves to reduce bending of the component due to different thermal expansion of the CFC and TZM during the brazing procedure and could possibly also enable remote controlled in-situ repair of damaged tiles in the confining vessel. The cooling tube of Mo41Re, bonded to the TZM heat sink by hot isostatic pressing (HIPing), contains a stainless steel twisted tape insert to enhance heat transfer into the water resulting in higher critical heat flux of the component. Thermal loading was carried out in the JAERI electron beam irradiation stand (JEBIS) at the Japan Atomic Energy Research Institute (JAERI). For the experiments the beam dimensions were chosen to be 5 × 15 cm 2 full width at half maximum. By stepwise increase of the power density at constant pulse lengths of 35 s the thermal response as well as the maximum tolerable heat load of the component were determined. The thermal fatigue behaviour was investigated by thermal cycling at 12 and 15 MW/m 2 power density. No change in thermal response was observed after 1000 cycles at 12 MW/m 2 and 300 cycles at 15 MW/m 2 surface heat flux, respectively.