The Proton Synchrotron Booster is made up of four superimposed synchrotron rings that receive beams of protons from the linear accelerator Linac 2 at 50 MeV and accelerate them to 1.4 GeV for injection into the Proton Synchrotron (PS).

Before the Booster received its first beams on 26 May 1972, protons were injected directly from the linac into the PS, where they were accelerated to 26 GeV. The low injection energy of 50 MeV limited the number of protons the PS could accept. The Booster allows the PS to accept over 100 times more protons, which greatly enhances the beam's use for experiments.