from the scientific community suggested to build a new Linac dedicated specifically to this task. The accelerated particles are mainly lead ions, which are provided to the LHC and fixed target experiments at the SPS and LEIR. For LEIR's commissioning, also oxygen ions were accelerated. After preparations from 2013 on, Linac 3 was adapted to accelerate argon ions in 2015. These were used by the NA61/SHINE experiment. Similarly, Linac 3 accelerated xenon ions in 2017 for NA61's fixed-target physics programme. On October 12, 2017, these were delivered to the Large Hadron Collider (LHC) for a unique run of data taking: For the first time, xenon ions were accelerated and collided in the LHC. For six hours, LHC's four experiments could take data of the colliding xenon ions. Linac 3 is expected to stay in use at least until 2022. Linac4 Linac4 (CERN uses this name/spelling), sometimes imprecisely referred to as Linac 4 (which is a name/spelling not used by CERN), is a current 86 metre-long linear accelerator that replaced the retired Linac 2. Unlike its predecessors, Linac4 accelerates negative hydrogen ions, not protons, and has an acceleration energy of 160 MeV. The ions are then injected to the Proton Synchrotron Booster (PSB) where both electrons are then stripped from each of the hydrogen ions and thus only the nucleus containing one proton remains. By using hydrogen ions instead of protons, the beam loss at the injection is reduced and simplified and this also allows more particles to accumulate in the synchrotron. CERN approved the construction of Linac4 in June 2007. Project started in 2008. Linac4 has been built in its own tunnel, parallel to Linac 2, in the main CERN site. The reason for building the accelerator in its own new tunnel is that its building could take place simultaneously with the operation of Linac 2. Linac4 has increased the energy by a factor of three over its predecessor, Linac 2, and achieve an energy of 160 MeV. This energy increase, when combined with the increased accumulation of particles, will enable the beam intensity to double when later delivered to LHC. This is part of the planned future luminosity increase of the LHC. The first injection of a particle beam from Linac4 into the PSB occurred in December 2020. External links CERN Video: Meet Linac4 CERN Video: Virtual Visit of the Linac4 in 3D References Particle physics facilities CERN accelerators