SIMION® is a software program for doing charged particles optics simulations. Mainly, it calculates 2D/3D electrostatic and certain magnetic fields and calculates the trajectories of charged particles through those fields. Low frequency (quasistatic) fields such as in the oscillating voltages on a quadrupole are supported as well. collision models and other special effects can be simulated though the user programming feature. SIMION provides a programming, visualization, and data recording environment for these simulations.

SIMION’s methods are fairly direct via finite difference methods (optimized over-relaxation and multimesh methods) and Runge-Kutta for solving the required partial differential equations (PDEs), particularly the Laplace Equation, and ordinary differential equations (ODEs) respectively. A workbench strategy allows multiple meshes, or possibly different mesh size and symmetry, to be used in the same simulation. The user programming feature allows these methods to be extended. Geometries can be defined via multiple methods.

SIMION is designed to be a very versatile and affordable tool. It is used widely for the design of spectrometer components and lens systems.

SIMION was originally developed by David Dahl at what is now Idaho National Labs. It is now developed by Scientific Instrument Services, Inc. (SIS).