This work studies the angle dependence of the interactions between impinging CH2 particles of 150 eV with the tungsten surface. The simulations show that the carbon atoms are much more easily bonded to the tungsten at...This work studies the angle dependence of the interactions between impinging CH2 particles of 150 eV with the tungsten surface. The simulations show that the carbon atoms are much more easily bonded to the tungsten atoms than hydrogen atoms, though a few of the latter can also penetrate into the tungsten material. When the incidence angle is greater than 75%, the incident CH2 particles are reflected without break-ups. Below this angle, a W-C layer of about 0.5 nm is formed with another C, H-rich layer depositing on top of it. The molecular dynamics （MD） approach has proved to be a powerful tool to solve the structural problems at atomic length scale of various materials. Some of its possible applications to the railway track materials have also been discussed.展开更多
Tungsten was exposed to pure Ar or Ne plasmas over 1550 K at several incident ion energies. Even under the irradiation condition that the tungsten nanostructure is formed by He plasma irradiation, holes/bubbles and fi...Tungsten was exposed to pure Ar or Ne plasmas over 1550 K at several incident ion energies. Even under the irradiation condition that the tungsten nanostructure is formed by He plasma irradiation, holes/bubbles and fiberform nanostructures were not formed on the surface by exposure to Ar or Ne plasmas. In addition, the results from energy dispersive X-ray spectroscopy supported the facts that Ar and Ne did not remain in the sample. We will discuss the reason for the differences in the damage to the tungsten surface exposed to noble gas plasmas.展开更多
Tungsten will be used as the plasma-facing divertor material in the International Thermonuclear Experimental Reactor(ITER)fusion reactor.Under high temperatures and high ion fluxes,a‘fuzz’nanostructure forms on the ...Tungsten will be used as the plasma-facing divertor material in the International Thermonuclear Experimental Reactor(ITER)fusion reactor.Under high temperatures and high ion fluxes,a‘fuzz’nanostructure forms on the tungsten surface with dramatically different properties and could contaminate the plasma.Although simulations and experimental observations have provided understanding of the initial fuzz formation process,there is debate over whether tungsten or helium migration is rate-limiting during late-stage growth,and the mechanisms by which tungsten and helium migrations occur.Here,the proposed mechanisms are considered in turn.It is concluded that tungsten migration occurs by adatom diffusion along the fuzz surface.Continual helium migration through the porous fuzz to the tungsten bulk is also required for fuzz growth,for continued bubble growth and rupture.Helium likely migrates due to ballistic penetration,although diffusion may contribute.It is difficult to determine the limiting process,which may switch from helium penetration to tungsten adatom diffusion above a threshold flux.Areas for further research to clarify the mechanisms are then considered.A greater understanding of the fuzz formation mechanism is key to the successful design of plasma-facing tungsten components,and may have applications in forming porous tungsten catalysts.展开更多
基金financially supported by the Science Foundation for International Cooperation of Sichuan Province (2014HH0016)the Fundamental Research Funds for the Central Universities (SWJTU2014: A0920502051113-10000)National Magnetic Confinement Fusion Science Program (2011GB112001)
文摘This work studies the angle dependence of the interactions between impinging CH2 particles of 150 eV with the tungsten surface. The simulations show that the carbon atoms are much more easily bonded to the tungsten atoms than hydrogen atoms, though a few of the latter can also penetrate into the tungsten material. When the incidence angle is greater than 75%, the incident CH2 particles are reflected without break-ups. Below this angle, a W-C layer of about 0.5 nm is formed with another C, H-rich layer depositing on top of it. The molecular dynamics （MD） approach has proved to be a powerful tool to solve the structural problems at atomic length scale of various materials. Some of its possible applications to the railway track materials have also been discussed.
文摘Tungsten was exposed to pure Ar or Ne plasmas over 1550 K at several incident ion energies. Even under the irradiation condition that the tungsten nanostructure is formed by He plasma irradiation, holes/bubbles and fiberform nanostructures were not formed on the surface by exposure to Ar or Ne plasmas. In addition, the results from energy dispersive X-ray spectroscopy supported the facts that Ar and Ne did not remain in the sample. We will discuss the reason for the differences in the damage to the tungsten surface exposed to noble gas plasmas.
基金The author thanks A.L.Greer for his time and support.This work was produced as part of the author’s studies for the MSci in Materials Science at the University of Cambridge.
文摘Tungsten will be used as the plasma-facing divertor material in the International Thermonuclear Experimental Reactor(ITER)fusion reactor.Under high temperatures and high ion fluxes,a‘fuzz’nanostructure forms on the tungsten surface with dramatically different properties and could contaminate the plasma.Although simulations and experimental observations have provided understanding of the initial fuzz formation process,there is debate over whether tungsten or helium migration is rate-limiting during late-stage growth,and the mechanisms by which tungsten and helium migrations occur.Here,the proposed mechanisms are considered in turn.It is concluded that tungsten migration occurs by adatom diffusion along the fuzz surface.Continual helium migration through the porous fuzz to the tungsten bulk is also required for fuzz growth,for continued bubble growth and rupture.Helium likely migrates due to ballistic penetration,although diffusion may contribute.It is difficult to determine the limiting process,which may switch from helium penetration to tungsten adatom diffusion above a threshold flux.Areas for further research to clarify the mechanisms are then considered.A greater understanding of the fuzz formation mechanism is key to the successful design of plasma-facing tungsten components,and may have applications in forming porous tungsten catalysts.
