Linear accelerator 3 (Linac3) 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 also requested the delivery of other ions, such as argon and xenon in the past and oxygen in the future.

The linear accelerators at CERN have swapped and changed roles over the years. After Linac2 was built, Linac1 was used to deliver ions for experiments at the Super Proton Synchrotron (SPS). There was soon pressure to provide heavier ions to study quark–gluon plasma, so the dedicated Linac3 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.

The ions are produced in Linac3’s source, where electrons are removed from the atoms inside a plasma. The source uses about 500 milligrams of lead per two weeks of operation.

Linear accelerators use the electric fields that are present in radio waves to accelerate the charged particles. When the waves are confined into conducting cavities, they can build up to high field strengths. The cavities can also contain magnets that ensure the particles remain focused over the tens of metres needed for acceleration.

Eventually, before entering the SPS, all of the electrons are removed and the lead ions are transformed into bare nuclei, which is more efficient to accelerate than partially ionised ions.