Effect of Surface Damage on Thermal Response of Tungsten Monoblocks

In this study, surface damaged W monoblocks (melting and cracking) by a pulsed plasma gun and an e-beam devices were exposed to cyclic heat loads (simulating normal heat loads and slow transients) and pulsed heat loads (simulating ELMs) to observe the effects of surface damage on surface erosion and heat removal capability.  Heat load tests simulating the normal heat load (10 MW/m², 10 sec, 300 cycles) and the slow transient (~20 MW/m², 10 sec, 300 cycles) were performed by the e-beam. The surface morphology changes after the heat load tests were observed using laser scanning microscopy and FE-SEM. After e-beam irradiation of ~20 MW/m², the longitudinal cracks crossing over entire monoblocks appeared on the surfaces of all monoblocks. Recrystallization and additional crack formation were also observed on the surface. However, there was no significant change of heat removal capability. In the additional pulsed heat load test, the energy fluence of 0.042-0.30MJ/m² was applied with pulse numbers of 10³ and 10⁴.The surface morphology changes after laser irradiation were observed using laser scanning microscope. After laser irradiation, the grain ejection occurred above a certain energy fluence (~25 % of melting threshold).