Sputtering properties of copper-lithium alloys at reactor-level temperatures and surface erosion rates

Abstract

Previous experiments on copper-lithium alloys at temperatures up to 250 °C and with erosion rates of 0.01–0.1 monolayer/s for 3 keV Ar+ bombardment have shown that in the electric and magnetic field environment of a magnetic-confinement fusion reactor, it is possible to maintain a lithium overlayer which will significantly reduce the copper erosion rate. We have extended these experiments to the reactor-relevant regime of 350–400 °C, with erosion rates approaching one monolayer/s (1.5 keV Ar+ bombardment at 2.1× 1014/cm2s., normal incidence). By comparison with the lower-fluxexperiments, it is found that radiation damage effects start to dominate both the surface concentration and depth profile of the lithium. The subsurface region of enhanced lithium concentration is broadened, while the surface concentration is not depleted as rapidly per incident ion as in the low-flux case. The time-dependent lithium depth profile is calculated using a computer code developed at Argonne which includes both Gibbsian segregation and radiation-induced effects. The experimental results are compared with these calculations. It is found that the sputtering behavior of the copper-lithium alloys is highly dependent on the mass and energy spectrum of the incident particles, the sample temperature, subsurface structure, and the partial sputtering yields of the alloy components.