Energy limitation for models to simulate the buffer gas cooling

<div>Detailed simulations of buffer gas cooling, which is widely applied at the rare-isotope facilities, have&nbsp;been investigated by using three frequently used models: viscous damping force (VDF) model, hard&nbsp;sphere collision (HSC) model, and realistic interaction potential (RIP) model. By comparing the stopping&nbsp;ranges from the simulated data with those from SRIM code, we found that the VDF and HSC models are&nbsp;better in low energy range, but the RIP model is better in relatively high energy range. In helium buffer&nbsp;gas, which is always used in cooler and bunchers, the VDF model should be used when the ion&rsquo;s energy&nbsp;is less than&nbsp;&sim;5 eV/u, and the RIP model less than</div><div>&sim;80 eV/u. Above this energy, all three models cannot be</div><div>used.