Observation of dust particles ejected from the tungsten surface by transient heat flux with small-angle scattering of cw laser light

A new test facility for experimental simulation of transient heat load expected in the ITER divertor during unmitigated events is developed. Application of a long-pulse (0.1–0.3ms) wide-aperture (up to 2cm2) electron beam as a heating device provides powerful energy loads at a tungsten target with FHF> 250MJm−2s−0.5. Dynamics of tungsten particles in the ablation plume is investigated with a novel for PSI experiments small-angle laser light scattering technique. The threshold of intense droplet generation and dynamics of particles sizes are estimated

In-situ imaging of tungsten surface modification under ITER-like transient heat loads

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

Calculation of Cracking inTungsten Manufactured According to ITER Specifications Under Pulsed Heat Load

A mathematical model of surface cracking under pulsed heat load was developed. The model correctly describes a smooth brittle–ductile transition. The elastic deformation is described in a thin-heated-layer approximation. The plastic deformation is described with the Hollomon equation. The time dependence of the deformation and stresses is described for one heating–cooling cycle for a material without initial plastic deformation.The model can be applied to tungsten manufactured according to ITER specifications. The model shows that the stability of stress-relieved tungsten deteriorates when the base temperature increases. This proved to be a result of the close ultimate tensile and yield strengths. For a heat load of arbitrary magnitude a stability criterion was obtained in the form of condition on the relation of the ultimate tensile and yield strengths