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

Previous experiments on copper-lithium alloys at temperatures up to 2500C and with erosion rates of .01 to .1 monolayer per second 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 to 4000C, with erosion rates approaching one monolayer per second. By comparison with the lower flux experiments, 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 alloy 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