The Large Hadron Collider

The Large Hadron Collider (LHC) is the most complex instrument ever built for particle physics research. It will, for the first time, provide access to the TeV-energy scale. Numerous technological innovations are necessary to achieve this goal. For example, two counterrotating proton beams are guided and focused by superconducting magnets whose novel two-in-one structure saves cost and allowed the machine to be installed in an existing tunnel. The very high (>8-T) field in the dipoles can be achieved only by cooling them below the transition temperature of liquid helium to the superfluid state. More than 80 tons of superfluid helium are needed to cool the whole machine. So far, the LHC has behaved reliably and predictably. Single-bunch currents 30% above the design value have been achieved, and the luminosity has increased by five orders of magnitude. In this review, I briefly describe the design principles of the major systems and discuss some initial results.