Manufacturing & high heat flux testing of tungsten brazed mockups in KSTAR

Development of tungsten brazing technology for the upgraded KSTAR divertor was launched in early 2013. ITER grade tungsten block was brazed on the CuCrZr alloy in vacuum at 980 °C for 30 minutes using silver free brazing alloy. A OFHC-copper was used as an interlayer between tungsten and the CuCuZr. The brazing alloy is a 0.05 mm thickness of plate of which component is a Ni-Cu-Mn. It is found that the optimal surface roughness on tungsten is about 6 µm Rs and the optimal loading on mock-up is about 20 kPa. Ultrasonic test, shear strength test, tensile strength test, and bend strength test were carried out to check the strength between tungsten and substrate material. And the joint conditions were analysed by scanning electron microscopy. Tungsten brazed mock-ups with a cooling tube were tested at the electron beam facility, KoHLT-EB in KAERI. The high heat flux test was performed for tungsten brazed mock-ups under heat flux of about 5 MW/m2 with more than 2,000 cycles. All the tungsten brazed mock-ups met the requirements and there was no delamination or failure at the bonding joints.