Nuclear Materials and Energy (Aug 2017)
In-situ imaging of tungsten surface modification under ITER-like transient heat loads
Abstract
Experimental research on behavior of rolled tungsten plates under intense transient heat loads generated by a powerful (a total power of up to 7 MW) long-pulse (0.1–0.3ms) electron beam with full irradiation area of 2 cm2 was carried out. Imaging of the sample by the fast CCD cameras in the NIR range and with illumination by the 532nm continuous-wave laser was applied for in-situ surface diagnostics during exposure. In these experiments tungsten plates were exposed to heat loads 0.5–1MJ/m2 with a heat flux factor (Fhf) close to and above the melting threshold of tungsten at initial room temperature. Crack formation and crack propagation under the surface layer were observed during multiple exposures. Overheated areas with excessive temperature over surrounding surface of about 500K were found on severely damaged samples more than 5ms after beam ending. The application of laser illumination enables to detect areas of intense tungsten melting near crack edges and crack intersections.