Design options to mitigate deep cracking of tungsten armor

Recent high heat flux (HHF) tests showed that the tungsten monoblock armor often suffered from deep cracking, when the applied HHF load approached 20 MW/m2. The deep cracks were initiated at the armor surface and grew toward the cooling tube. The deep cracking seemed not to affect the heat removal capability of tungsten divertor, as most of the cracks were perpendicular to the loading surface. However, the inherently unstable nature of brittle cracking may likely increase the risk of structural failure. In this work, three variants (reduction in width of armor, inverse trapezoid shape in the lower part and castellation) of full-W divertor armor design based on the ITER divertor design are proposed to mitigate deep cracking at 20 MW/m2. The temperature, stress and strain fields are simulated with finite element method. The possibilities of crack initiation and propagation are evaluated by calculating the low cycle fatigue lifetime and J-integrals, respectively. All three variants can mitigate deep cracking of tungsten armor.