Optimization of the chamfering structures for ITER-like W/Cu monoblocks to avoid the leading edge-induced melting in EAST.

• Leading edge-induced melting of W/Cu monoblocks was found only at inter-CMs. • Thermal analysis identified the current dual chamfer shaping structure (1 mm × 1 mm) did not work as-intend at inter-CMs. • The symmetric CMs with different chamfer solutions at inter-CMs and intra-CM have been proposed to effectively improve the thermal performance of the upper W divertor in EAST. EAST has installed a full ITER-like W divertor with W/Cu monoblocks for targets in the upper part of vacuum chamber since 2014. Although the dual chamfer shaping structure with 1 mm cutting in both toroidal and radial directions (1 mm × 1 mm) has been employed to mitigate the leading edge-induced thermal effect, severe leading edge-induced melting was widely observed on both inner and outer targets. All melting only occurred at the leading edges between neighboring cassette modules (inter-CMs), while it was not found at the leading edges between neighboring monoblocks within one cassette module (intra-CM). To optimize the chamfering structure for avoiding melting, thermal analysis of W/Cu monoblocks was performed by finite element method. It is identified that the current dual chamfer shaping structure (1 mm × 1 mm) does not work for inter-CMs due to the large radial misalignment which was hardly controlled and could even reached up to 3 mm. With such large misalignment, the maximum surface steady state heat load is only 1.2 MW m−2 for current structure. Thus, a symmetric structure of CMs which survive EAST operations requirement with two different toroidal magnetic fields has been proposed to improve the thermal performance and avoid melting. At inter-CMs, the optimized chamfering structure suitable for larger misalignments and heat fluxes has been suggested. And, the current dual chamfer shaping structure is remained at intra-CM after thermal evaluation. Such symmetric CMs should ensure EAST operate with heat flux up to 3 MW m−2 with 3 mm misalignment level. And, further improvement to withstand a higher heat flux is also proposed and discussed. [ABSTRACT FROM AUTHOR]