An example particle therapy system includes a particle accelerator to output a particle beam, where the particle accelerator includes: a particle source to provide pulses of ionized plasma to a cavity, where each pulse of the particle source has a pulse width corresponding to a duration of operation of the particle source to produce the corresponding pulse, and where the particle beam is based on the pulses of ionized plasma and a modulator wheel having different thicknesses, where each thickness extends across a different circumferential length of the modulator wheel, and where the modulator wheel is arranged to receive a precursor to the particle beam and is configured to create a spread-out Bragg peak for the particle beam
