The Large Hadron Collider

This chapter discusses the design principles of the LHC, which gives access to the TeV energy scale for the first time. To achieve this, a number of technological innovations have been necessary. Two counter-rotating proton beams are guided and focused by superconducting magnets with a two-in-one structure allowing the machine to be installed in an existing tunnel. The very high field (>8 T) in the dipoles can only be achieved by cooling them below the superfluid transition temperature of liquid helium. More than 80 tons of superfluid helium is needed to cool the machine. In its first year of operation, the LHC has behaved very reliably and predictably. Single-bunch currents 30% above the design value have already been achieved, and the luminosity has increased by five orders of magnitude in the first 200 days of operation. Some of the results of commissioning and first operation are also discussed.