  The cryogenic buffer gas beam (CBGB) is an important tool in the study of
cold and ultracold molecules. While there are known techniques to enhance
desired beam properties, such as high flux, low velocity, or reduced
divergence, they have generally not undergone detailed numerical optimization.
Numerical simulation of buffer gas beams is challenging, as the relevant
dynamics occur in regions where the density varies by orders of magnitude,
rendering standard numerical methods unreliable or intractable. Here, we
present a hybrid approach to simulating CBGBs that combines gas dynamics
methods with particle tracing. The simulations capture important properties
such as velocities and divergence across an assortment of designs, including
two-stage slowing cells and de Laval nozzles. This approach should therefore be
a useful tool for optimizing CBGB designs across a wide range of applications.
