Clamping of solid tungsten components for the bulk W divertor row in JET—precautionary design for a brittle material

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For the bulk tungsten divertor row, a development for the ITER-like wall in JET, utmost care was taken to limit the stresses in the solid tungsten plasma-facing components. The bulk W tile is located at the position of the outer strike point for most envisaged plasma configurations. The absence of active cooling makes temperature cycling of the refractory tungsten material close to or through the ductile-to-brittle transition temperature (about 200–300 °C) and above the recrystallization threshold around 1250 °C hardly avoidable.The clamping concept is aimed at subjecting tungsten exclusively to compression forces. Each tile is segmented in stacks of 24 solid lamellae. The vertical clamping forces and the compressive preload for the stack integrity generate uniform pressures <6–20 MPa. Loads resulting in higher forces were deliberately moved to the supporting structure. The goal of minimizing tensile stresses in tungsten was achieved to the greatest extent, which results in thermo-mechanical values below 150 MPa.