The Proton Synchrotron Booster is made up of four superimposed synchrotron rings that receive beams of negative hydrogen ions (H-, consisting of a hydrogen atom with an additional electron) from the linear accelerator Linac4 at 160 MeV. The ions are stripped of their two electrons during injection from Linac4 into the Proton Synchrotron Booster to leave only protons, which are accelerated to 2 GeV for injection into the Proton Synchrotron (PS).
Before the Booster received its first beams on 26 May 1972, protons were injected directly from Linac1 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. From 1978 until 2018, the Booster received protons from Linac2 at 50 MeV and accelerated them to 1.4 GeV for injection into the PS.
The Booster allows the PS to accept over 100 times more protons, which greatly enhances the beam's use for experiments.