F. Rodriguez-Mateos

Test results on 10 T LHC superconducting one metre long dipole models

Superconducting twin-aperture dipole model magnets for the CERN future superconducting collider, the Large Hadron Collider (LHC), were built. The authors report on the magnet quench behavior and the field measurements at low and high magnetic induction. They describe the results obtained with 1-m-long models which have been made in industry. To test different design ideas, four magnets were built with a number of technical variants relating to the type of cable and electrical insulation, details in coils, material, shape and assembly method of the collars and the material of the outer shrinking cylinder. Tests performed on two magnets called MTA-JS and MTA-H are discussed. Measurements of the losses in the superconducting cables and the quenching field at various field ramp rates are used to investigate the temperature margin in superfluid helium under steady-state losses.<<ETX>>

Energy extraction for the LHC superconducting circuits

The superconducting magnets of the LHC will be powered in about 1700 electrical circuits. The energy stored in circuits, up to 1.3 GJ, can potentially cause severe damage of magnets, bus bars and current leads. In order to protect the superconducting elements after a resistive transition, the energy is dissipated into a dump resistor installed in series with the magnet chain that is switched into the circuit by opening current breakers. Experiments and simulation studies have been performed to identify the LHC circuits that need energy extraction. The required values of the extraction resistors have been computed. The outcome of the experimental results and the simulation studies are presented and the design of the different energy extraction systems that operate at 600 A and at 13 kA is described.

Cryogenic tests of the first two LHC quadrupole prototypes

Two LHC (Large Hadron Collider) twin aperture quadrupole superconducting magnet prototypes were constructed at CEA Saclay, in the framework of a collaboration agreement between CERN and CEA in Saclay. Their main characteristics are: 3.05 m length, 56 mm coil aperture, 180 mm between the two apertures, 252 T/m nominal gradient at 15060 A. They have been tested and measured in the 1.8 K Saclay test facility in a horizontal cryostat. The magnets are instrumented in order to investigate their behaviour during cool-down, stand-by, powering and current ramping, quenching and warming-up. The paper presents a summary of the cryogenic, mechanical, pressure and electrical measurements. The 15060 A nominal current was reached with little training. The quench protection heaters are efficient down to 3000 A. Losses during ramping up and down are reported.<<ETX>>

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.

The quench protection system for the LHC test string 2

The large hadron collider (LHC) string program has focused over the years the efforts of many teams that have tested and validated their systems under operating conditions close to the final ones in the LHC machine tunnel and underground areas. During the various phases while commissioning or performing dedicated experiments, the quench protection system (QPS) has been tested and improved. A large variety of designs of the QPS equipment have been validated. The experience gained, especially concerning both the commissioning and the interaction with systems working within close interfaces (interlocks, powering, controls), is a valuable expertise to undertake the LHC challenge. In the LHC, the QPS will be the only system monitoring and protecting the superconducting elements: the integrity of all the superconducting magnets, bus bars and high-T/sub c/ superconducting current leads will depend on its reliable operation. A description of the system installed in String 2 will be given together with the principal similarities and differences with respect to the equipment planned for installation in the LHC. The key experimental results will be explained.

A Statistical Analysis of Electrical Faults in the LHC Superconducting Magnets and Circuits

The large hadron collider (LHC) at CERN has been operating and generating physics experimental data since September 2008, and following its first long shut down, it has entered a second, 4-year-long physics run. It is to date the largest superconducting installation ever built, counting over 9000 magnets along its 27-km long circumference. A significant operational experience has been accumulated, including the occurrence and consequences of electrical faults at the level of the superconducting magnets, as well as their protection and instrumentation circuits. The purpose of this paper is to provide a first overview of the most common electrical faults and their frequency of occurrence in the first years of operation, and to perform a statistical analysis that can provide reference values for future productions of similar dimensions and nature.