Self-sustaining coatings for fusion applications: Copper lithium alloys

Auger electron spectroscopy was used to monitor the surface composition of an alloy consisting of 3.0 at. % Li in Cu while sputtering with 1 to 3 keV Ar(+) or He(+) at a flux of 10(12) to 10(14) cm(-2) sec(-1) (corresponding to a gross erosion rate of several mm/yr) at temperatures up to 430(0) C. It is found that the alloy is capable of reproducibly maintaining a complete lithium overlayer. The time dependent thickness of the overlayer depends strongly on the mass and energy spectrum of the incident particle flux. It was experimentally demonstrated that a significant fraction of the sputtered lithium is in the form Li(+) and is returned to the surface by an electric field such as the sheath potential at the limiter, or a tangential magnetic field such as the toroidal field at the first wall; consequently, the overlayer lifetime is essentially unlimited. The TRIM computer code was used to calculate the sputtering yield for pure metals and the partial sputtering yields of binary alloy components for various assumed solute concentration profiles.