A Study of plasma facing tungsten components with electrical discharge machined surface exposed to cyclic thermal loads

Seki, Yohji; Ezato, Koichiro; Suzuki, Satoshi; Yokoyama, Kenji; Yamada, Hirokazu; Hirayama, Tomoyuki

Through R&D for a plasma facing unit (PFU) of an ITER full-tungsten (W) divertor, Japan Atomic Energy Agency (JAEA) succeeded in demonstrating the durability of the cyclic heat loaded W divertor which was shaped by an electrical discharge machining (EDM). To prevent melting of W, an adequate technology to meet requirements of a geometrical shape and tolerance of the PFU is one of the most important key issues in a manufacturing process. JAEA has evaluated the EDM to control the final shape tolerance of 0.25 mm. In order to examine an effect on durability of the micro-crack due to EDM, one polished W armor without the EDM and three W armors with the EDM were exposed to cyclic thermal loads. As the result, all of the W armors endured the repetitive heat load of 20 MW/m 1000 cycles without any macro-cracks, which strongly encourages the realization of the PFU of ITER full-W divertor with various geometrical shape and high accuracy tolerance.