Directly-cooled VPS-W/Cu limiter and its preliminary results in HT-7

Tungsten (W) coatings on copper (Cu) substrate have been developed by means of vacuum plasma spraying (VPS) method employing a composition gradient interlayer so as to alleviate mismatch of the physical properties between Cu and W. The gradient interlayer shows dense and lamellar microstructure and the coating surface few microcracks. Directly-cooled VPS-W/Cu plasma-facing component (PFC) can withstand e-beam high heat flux (HHF) irradiation of 20 cycles, 100 s/cycle, and heat loads of 9.6 MW/m2. The PFC joined to a newly modified motion mechanism as a movable limiter was then tested in HT-7 and showed good integrity under the ohmic plasmas. Heat deposition onto the limiter has been investigated and a simplified model proposed to explain qualitatively the surface temperature behavior observed by an IR camera. The model estimates the heat load onto each round edge of the PFC to be about 10 MW/m2.