Energy limitation for models to simulate the buffer gas cooling

► Viscous damping force (VDF) model, hard sphere collision (HSC) model, and realistic interaction potential (RIP) model. ► The VDF and HSC models are better in low energy range, but the RIP model is better in relatively high energy range. ► In helium buffer gas, the VDF model should be used when the ion's energy is less than ∼5 eV/u, and the RIP model less than ∼80 eV/u. Above this energy, all three models cannot be used. ► If the buffer gas becomes heavier, the upper limits to use the models decrease.