The accelerator complex at
CERN is a succession of machines with increasingly higher energies. Each machine
injects the beam into the next one, which takes over to bring the beam to an
even higher energy, and so on. In the LHC—the last element of this chain—each
particle beam is accelerated up to the record energy of 7 TeV [eventually!]. In
addition, most of the other accelerators in the chain have their own
experimental halls, where the beams are used for experiments at lower energies.
1. The brief story of a proton accelerated through the accelerator complex at CERN is as follows:
- Hydrogen atoms are taken from a bottle containing hydrogen. We get protons by stripping orbiting electrons from hydrogen atoms.
- Protons are injected into the PS Booster (PSB) at an energy of 50 MeV from Linac2. The booster accelerates them to 1.4 GeV.
- The beam is then fed to the Proton Synchrotron (PS) where it is accelerated to 25 GeV.
- Protons are then sent to the Super Proton Synchrotron (SPS) where they are accelerated to 450 GeV.
- They are finally transferred to the LHC (both in a clockwise and an anticlockwise direction, the filling time is 4’20’’ per LHC ring) where they are accelerated for 20 minutes to their nominal energy of 7 TeV. Beams will circulate for many hours inside the LHC beam pipes under normal operating conditions.
- Protons arrive at the LHC in bunches, which are prepared in the smaller machines.
2. In addition to accelerating protons, the accelerator complex also accelerates lead ions.
- Lead ions are produced from a highly purified lead sample heated to a temperature of about 500°C. The lead vapour is ionized by an electron current. Many different charge states are produced with a maximum around Pb29+.
- These ions are selected and accelerated to 4.2 MeV/u (energy per nucleon) before passing through a carbon foil, which strips most of them to Pb54+.
- The Pb54+ beam is accumulated, then accelerated to 72 MeV/u in the Low Energy Ion Ring (LEIR), which transfers them to the PS.
- The PS accelerates the beam to 5.9 GeV/u and sends it to the SPS after first passing it through a second foil where it is fully stripped to Pb82+.
- The SPS accelerates it to 177 GeV/u then sends it to the LHC, which accelerates it to 2.76 TeV/u.