R. Saban

The commissioning of the LHC test string 2

String 2 is a full-size model of an LHC cell of the regular part of the arc. It is composed of six dipole magnets with their correctors, two short straight sections with their orbit and lattice corrector magnets, and a cryogenic distribution line running alongside the magnets. The commissioning of String 2 Phase 1, with one half-cell and the following quadrupole, has started in April 2001. As for String 1, the facility was built to individually validate the LHC systems and to investigate their collective behaviour during normal operation (pumpdown, cool-down and powering) as well as during exceptional conditions such as quenches. String 2 is a stepping stone towards the commissioning of the first sector (one eight of LHC) planned for 2004. It is expected to yield precious information on the infrastructures, the installation, the tooling and the procedures for the assembly, the testing and the commissioning of the individual systems, as well as the global commissioning of the technical systems. This paper describes the procedures followed for the commissioning and details the preparation for the first cool-down and for the powering.

The LHC magnet string programme: status and future plans

String 1, with one twin aperture quadrupole and three twin aperture 10-m dipoles (MB1, MB2 and MB3) powered in series and operating at 1.9 K, has recently been dismantled after four years of operation interrupted by technical stops and shutdowns for upgrading or exchanging equipment. Following the validation of the main LHC systems (cryogenics, magnet protection, vacuum, powering and energy extraction) the experimental programme was oriented towards the optimisation of the design and the observation of artificially induced fatigue effects. The design study for String 2 has been completed. This facility, which will be commissioned in December 2000, is composed of two LHC half-cells each consisting of one twin aperture quadrupole and three 15-m twin aperture dipoles. A cryogenic distribution line housing the supply and recovery headers runs parallel to the string of magnets. An electrical feedbox is used to power, with high temperature superconductor current leads, the circuits as in the regular part of an LHC arc. This paper reviews the experiments carried-out with String 1 and summarises the results obtained after more than 12800 hours of operation below 1.9 K and 172 quenches. It also describes the layout and the components of String 2 and explains the objectives pursued by its designers.

First powering of the LHC Test String 2

String 2 is a full-size model of a regular cell in an LHC arc. In the first phase, three dipole magnets and two quadrupole magnets have been assembled in String 2 and commissioning started in April 2001. By the beginning of 2002 three pre-series dipole magnets will be added to complete the cell. As for its predecessor String 1, the facility was built to individually validate the LHC systems and to investigate their collective behavior for normal operation with the magnets at a temperature of 1.9 K, during transients as well as during exceptional conditions. String 2 is a precious milestone before installation and commissioning of the first LHC sector (1/8 of the machine) in 2004, with respect to infrastructure, installation, tooling and assembly procedures, testing and commissioning of individual systems, as well as the global commissioning of the technical systems. This paper describes the commissioning, and retraces the first powering history.