High heat flux testing of mm thick tungsten coatings on carbon-fiber composites for the JT-60SA tokamak

High heat flux tests have been performed on 0.4 mm thick W coatings produced by vacuum plasma spraying on carbon-fiber composites (CFCs) for the future actively cooled W-coated CFC divertor target in JT-60SA. The surface temperature of the W coating increased up to 2000 °C at 15 MW m⁻² for 5 s. No severe morphological changes, for example, melting, cracking and delamination were observed although recrystallization and grain growth were found in the W coating. Cyclic loading at 15 MW m⁻² for 3 s with 50 cycles and additional 50 cycles with longer pulse length of 4 s produced again no severe morphological changes. Heat transfer analysis of the W-coated CFC sample during the high heat flux test showed that thermal resistance between W coatings and CFCs was negligibly low. This analysis also showed that the surface temperature of the 1 mm thick W coating on the actively cooled CFC monoblock divertor target in JT-60SA will be higher than the recrystallization temperature, 1200 °C, at the steady state heat flux of 15 MW m⁻². Therefore, a reduction of armor thickness of the future actively cooled W-coated CFC monoblock divertor target in JT-60SA could be necessary to decrease the surface temperature to less than the recrystallization temperature.