Calculations of damage to rotating targets under intense beams for super-heavy element production

In the production of the heaviest elements, the cross-sections for evaporation residues are very small, which, in turn, requires the usage of intense beams. Hence, the targets used tend to exhibit shortened lifetimes as beam currents are raised. Tightly focused beams on stationary targets of modest melting point and/or high sputtering yield material will eventually melt or destroy the target. Defocused or "wobbled" beams enhance target survival only to a modest degree. Rotating the target on a wheel can overcome target melting, and using, in addition, a low sputtering rate material as a covering layer can address this issue and allow for higher beam currents to be used for experiments. The purpose of the calculations done for this work is to attempt to predict the safe range of beam currents allowable, i.e. currents which produce heat loads below the melting point of the target. Materials with favorable sputtering rates and thermal properties are also examined. Calculations of the heating and sputtering these targets can withstand will show the safe limits to which they may be exposed and still survive.