Molecular dynamics simulations for laser-cooled sources

Electron and ion sources based on laser-cooling and trapping techniques are a relatively new reality in the field of charge particle accelerators. The dynamics of these sources is governed by stochastic effects, and not by the usually dominant space-charge forces. This is the direct consequence of the extremely high initial phase-space density. Correct simulation results require a full molecular dynamics simulation, i.e. we need to track each and every particle including all pair-wise interactions. The two main candidates for such molecular dynamics simulations are the Fast Multipole Method (FMM) and the Barnes&Hut scheme (B&H). Tradeoffs are given, and simulation results for the B&H method implemented in the General Particle Tracer (GPT) code are presented for realistic test-cases.