Effect of Fiber-Form Nanostructure on the Particle Emissions from Tungsten Surface in Plasmas

Abstract

The effects of fiber-form nanostructure of tungsten surface on both the electron emission and the sputtering in helium/argon plasmas are represented. Generally nano-fiber forest made of tungsten with helium gas inside was found to have a tendency of suppressing the particle emission. The electron emission comes from the impact of high energy primary electrons. In addition，a deeply biased tungsten target which inhibits the influx of even energetic primary electrons seems to produce an electron emission，and it may be suppressed on the way to nanostructure formation on the surface of W target. Such an emission process is discussed here. The sputtering yield of He-damaged tungsten surface with the fiber-form nanostructure depends on the surface morphology while the sputtering itself changes the surface morphology，so that the time evolutions of sputtering yield from the W surface with originally well-developed nanostructure was found to show a minimum in sputtering yield. The surface morphology at that time is for the first time made clear with FE-SEM observation. The physical mechanism for the appearance of such a minimum in sputtering yield is discussed.