FBPIC was designed specifically for simulations of laser-wakefield acceleration and plasma-wakefield acceleration. Therefore it provides helper functions and classes that allow to easily:
Inject a laser pulse in the simulation.
Initialize a relativistic electron beam with its space charge field.
Add external fields (e.g. focusing fields), which are applied to the particles at each timestep but are not self-consistently evolved by the simulation.
See the sections below for the corresponding documentation: