Linear accelerator 3 (Linac 3) is the starting point for the ions used in experiments at CERN. It provides lead ions for the Large Hadron Collider (LHC) and for fixed-target experiments. Researchers have requested that it produce other ions in the future, including argon and xenon.

Linear accelerators use radiofrequency cavities to charge cylindrical conductors. The ions pass through the conductors, which are alternately charged positive or negative. The conductors behind them push particles and the conductors ahead of them pull, causing the particles to accelerate. Superconducting magnets ensure the protons remain in a tight beam.

The linear accelerators at CERN have swapped and changed roles over the years. After Linac 2 was built, Linac 1 was used to deliver ions for experiments at the Super Proton Synchrotron. There was soon pressure to provide heavier ions to study quark-gluon plasma, so the dedicated Linac 3 was built. It started up in 1994, providing ions to the Proton Synchrotron Booster. It now injects lead ions into the Low Energy Ion Ring, which prepares them for injection into the LHC.

Linac 3 uses up about 500 milligrams of lead per two weeks of operation. At the particles’ origin and during acceleration through Linac 3, electrons are stripped away. Eventually, all of the electrons are removed and the lead is transformed into bare nuclei, which are easier to accelerate than whole ions.

Linac 3 is expected to be in use until at least 2022.