Surface Characteristics Of Bulk Metallic Glasses As First Mirror Materials For Fusion Reactor

Reflection mirrors, or first mirrors (FMs) as generally called, are be implemented in about half of the ITER diagnostic. First mirrors are subjected to intense irradiations that deteriorate the reflectivity of the diagnostic mirrors. The choice of proper material for the mirrors is crucial importance. Mirrors made from bulk metallic glasses are among the main candidates for use in ITER diagnostic systems operating under erosion-dominated conditions.In the present study, to check the anti-sputtering capability of the bulk metallic glasses under low temperature hydrogen plasma and high charge-state helium ions. Bulk amorphous alloys Co61.2B26.2Si7.8Ta4.8, Zr6.5A17.5Ni10Cu17.5and Zr63.7A19.0Ni27.3, as well as polycrystalline Mo were prepared by using arc melting pure constituent elements under an argon atmosphere. All the specimens were mechanically polished using diamond power with gradually decreased particle size. Before the hydrogen plasma exposure all the specimens were cleaned using glow discharge in Ar flow for organic surface contamination removal. The specular reflectivity, surface structure and surface root mean square roughness were measured before and during the plasma sputtering. Structural identification was carried out using XRD. The specular reflectivity was measured by M-2000ellipsometry. AFM was also used to unveil the surface topography and surface roughness.Compared to polycrystalline Mo, W and Zr-based bulk amorphous alloys Zr65A17.5Ni10Cu17.5and Zr63.7Al9.0Ni27.3, no significant changes in specular reflectivity were observed for the mirror made from the Co-B-based bulk amorphous alloys C061.2B26.2Si7.8Ta4.8after the exposures. The initial surface crystallization of the bulk metallic glasses after a short influx of ions is shown to reverse to amorphization upon further bombardments, unveiling an erosion-induced self-recovery amorphization mechanism that guarantees stable surface structures and henceforth stable reflectivities. XPS analysis showed that the deposition of impurity C, O elements on the surface of first mirrors would have influence on the specular reflectivity of bulk metallic glasses.