A complete cell of CERN’s Large Hadron Collider (LHC) began tests at the laboratory in June. String 2, as the cell is known, has been built to validate LHC systems and operating procedures. It succeeds an original string made up of early prototypes, which was dismantled in December 1998. The present facility was first operated last year, although without its full complement of magnets. The full cell now consists of six dipole magnets, two straight sections (each comprising a quadrupole and corrector magnets), a prototype cryogenic distribution line and an electrical feedbox.
In its original configuration, String 2 had only three dipoles, all of which were prototypes. The three dipoles that have been added to make up the full cell are pre-production magnets that will form part of the future accelerator. The full cell is almost 120 m long and it is curved like the future accelerator to mimic the LHC as closely as possible. The amount of instrumentation and the complexity of the String 2 processes are also close to those of an LHC sector.
First tests went according to plan. Following mechanical checks to ensure there were no leaks and that the string could withstand the pressures that occur during a transition from the superconducting to the normal state (a quench), the assembly was cooled down to its nominal temperature of 1.9 K in just under 10 days. Powering up the circuits then followed without incident, with the dipole circuit reaching its nominal current of 11,860 A, corresponding to a magnetic field of 8.335 T, on 17 June. An experimental programme that will run until the end of the year is now under way.
