Fig. 2: Start-to-end particle tracking simulations along the UCLA Pegasus beamline.
From: Towards higher frequencies in a compact prebunched waveguide THz-FEL

Top) Evolution of the x,y,z rms moments of the particle distribution. Bottom) Energy and energy spread of the beam along the beamline. Solid and dotted lines show transport of beamlets and smooth longitudinal profile, respectively.