Progress in 20 MW/m ² Testing of Outer Target Prototype for CRAFT Flat-Type Divertor

During the operation of a fusion reactor, the divertor is directly exposed to high-parameter plasma impacts and endures high heat flux (HHF). A flat-type divertor demonstrates superior heat transfer performance compared to a monoblock divertor. This study focuses on 20 MW/m2 testing of an outer target prototype of CRAFT flat-type divertor. The flat-type structure is fabricated from a combination of potassium-doped tungsten (KW), copper (Cu), oxide dispersion–strengthened copper (ODS-Cu), and reduced-activation ferritic/martensitic (RAFM) steel. Its heat transfer performance and thermal stability were investigated by numerical simulations and HHF testing. Simulation results indicated that under a heat flux of 20 MW/m2, the maximum temperatures of the KW, Cu, ODS-Cu, and RAFM layers were 1390°C, 537°C, 488°C, and 39°C, respectively. During the HHF testing, the recorded peak temperatures were 1405°C in the initial 50 cycles. The outer target prototype successfully endured 1000 steady-state cycles at 20 MW/m2 and 10 thermal shocks at 30 MW/m2. The overall structure and performance remained intact upon completion of the tests, and nondestructive examination revealed no defects exceeding an equivalent diameter of 2 mm. This study confirms that the outer target prototype possesses exceptional heat removal capability and structural reliability, providing critical data to support the design of target operating at 20 MW/m2.