Thermomechanical behaviour of actively cooled divertor elements with internal coolant flow return

For future fusion devices, target element specimens with a reversal of the coolant flow have been designed, manufactured and tested. Two parallel OFHC-Cu tubes connected with another at one end by a Cu flow reversal element brazed onto blocks of a 2-D Carbon Fibber reinforced Carbon (CFC) have been selected to realize such divertor elements. To estimate the thermal behaviour, heat load experiments were performed in the high heat flux ion beam facility MARION. Peak power densities up to 13 MW/m2 for 5, 10 and 20 s of the elliptic Gaussian shaped hydrogen ion beam have been applied to the target element specimens. After extreme heat loads, cracks in the 2-D CFC block occurred leading to a strong deformation of the CFC and a partial detachment of the Cu tubes. By using a castellated CFC materials and a large number of braze depots for the target elements no cracking of the CFC material took place and a good thermal performance up to power loads of more than 10 MW/m2 has been achieved.