Y.Z. Jia

Suppression of cavitation in melted tungsten by doping with lanthanum oxide

Melting and boiling behaviour of pure tungsten and 1 wt% lanthanum-oxide-doped tungsten (WL10) are investigated, focusing on the material selection with respect to material loss induced by cavitation. Melting experiments under high heat loads are carried out in the high heat flux facility GLADIS. Pulsed hydrogen neutral beams with heat flux of 10 and 23 MW m−2 are applied onto the adiabatically loaded samples for intense surface melting. Melt layer of the two tungsten grades exhibit different microstructure characteristics. Substantive voids owning to cavitation in the liquid phase are observed in pure W and lead to porous resolidified material. However, little cavitation bubbles can be found in the dense resolidified layer of WL10. In order to find out the gaseous sources, vapour collection is performed and the components are subsequently detected. Based on the observations and analyses, the microstructure evolutions corresponding to melting and vapourization behaviour of the two tungsten grades are tentatively described, and furthermore, the underlying mechanisms of cavitation in pure W and its suppression in WL10 are discussed.

Subsurface deuterium bubble formation in W due to low-energy high flux deuterium plasma exposure

The deuterium (D) bubbles formed in W exposed to high flux D plasma were researched by scanning electron microscopy and transmission electron microscopy. After D plasma exposure at 500 K and 1000 K, a layer of nano-sized bubbles were homogenously distributed in W subsurface region. The D bubbles were homogenously nucleated due to the high D concentration, and the nucleation process is not related to the vacancy defects. At low temperature (500 K), D bubbles can grow by surface blistering, which caused different nano scale morphologies on different surfaces. At high temperature (1000 K), D bubbles mainly grow by vacancy clustering, which caused pinholes on the surface.

Thermal shock behaviour of blisters on W surface during combined steady-state/pulsed plasma loading

The thermal shock behaviour of blister-covered W surfaces during combined steady-state/pulsed plasma loading was studied by scanning electron microscopy and electron backscatter diffraction. The W samples were first exposed to steady-state D plasma to induce blisters on the surface, and then the blistered surfaces were exposed to steady-state/pulsed plasma. Growth and cracking of blisters were observed after the exposure to the steady-state/pulsed plasma, while no obvious damage occurred on the surface area not covered with blisters. The results confirm that blisters induced by D plasma might represent weak spots on the W surface when exposed to transient heat load of ELMs. The cracks on blisters were different from the cracks due to the transient heat loads reported before, and they were assumed to be caused by stress and strain due to the gas expansion inside the blisters during the plasma pulses. Moreover, most of cracks were found to appear on the blisters formed on grains with surface orientation near [1 1 1].

Finite element modeling study of the suppression effect of external high magnetic field on the heat transfer of tungsten melt

Finite element modeling analysis has been employed to simulate the melt layer motion of tungsten and tungsten-based materials under high magnetic field. High heat flux of 2 GW m−2 was loaded for 3 ms at 1000 K and provided a molten bath. Meanwhile, high magnetic field from 0 to 8 T was loaded during the simulation. Both positive and negative surface tension temperature coefficient was tested. The result shows that the convention forced by the surface tension is suppressed by the magnetic field. The high magnetic field performs as a resistance of the heat transfer, leading to a reduced molten bath. The magnetic field mitigates the melting behaviur of the tungsten materials.