Whenever SLAC National Accelerator Laboratory's linear accelerator is on, packs of around a billion electrons each travel together at nearly the speed of light through metal piping. These electron bunches form the accelerator's particle beam, which is used to study the atomic behavior of molecules, novel materials and many other subjects. But trying to estimate what a particle beam actually looks like as it travels through an accelerator is difficult, leaving scientists often with only a rough approximation of how a beam will behave during an experiment. Now, researchers have developed an algorithm that more precisely predicts a beam's distribution of particle positions and velocities as it zips through an accelerator.