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The Large Hadron Collider (LHC) String program has focused on the validation of the Quench Protection System (QPS) in the LHC machine tunnel and underground areas. A description of the system installed in String 2 is focused along with the principal similarities and differences with respect to the equipment planned for installation in the LHC.

Research is presented describing the measurement of a 1-m model of the individually powered twin-aperture superconducting quadrupole for the Large Hadron Collider (LHC) insertions. The quadrupoles have a 70mm coil bore and must be inserted wherever increased geometrical acceptance is needed.

The design of a 1 m model of the low current superconducting quadrupole for the Large Hadron Collider insertions is described.

The quench protection capability of the third quadrupole of 1-meter superconducting magnets for the Large Hadron Collider has been tested at 4.4 K and at 1.9 K. Results indicate that the magnet trained well at 1.9 K at the first thermal cycle but not at 4.4 K. The magnet was able attain a gradient of 260 T/m at 1.9 K at the third cycle and retained its trained state. The protection strip heaters functioned adequately at 4.4 K and 1.9 K with delay times of 10 to 15 ms and 70 to 80 ms for low currents.

Within the framework of the Large Hadron Collider (LHC) R&D programme, CERN is performing experiments to establish the current carrying capability of irradiated diodes at liquid Helium temperatures for the superconducting magnet protection. Even if the diodes are degraded by radiation dose and neutron fluence, they must be able to support the by-pass current during a magnet quench and the de-excitation of the superconducting magnet ring. During this discharge, the current in the diode reaches a maximum value up to 13 kA and decreases with an exponential time constant of 100s. Two sets of 75 mm wafer diameter epitaxial diodes, one irradiated and one non-irradiated, were submitted to this experiment. The irradiated diodes have been exposed to radiation In the accelerator environment up to 20 kGy and then annealed at room temperature. After the radiation exposure the diodes had shown a degradation of forward voltage of 50 % which reduced to about 14 % after the thermal annealing. During the long duration high current tests, one of the diodes was destroyed and the other two irradiated diodes showed a different behaviour compared with non-irradiated diodes.

The first 10 metre long dipole prototypes made by European Industry within the framework of the R&D programme for the Large Hadron Collider (LHC) have been tested at CERN. As a part of the test programme, a series of quench protection tests have been carried out in order to qualify the basic protection scheme foreseen for the LHC dipoles (quench heaters and cold diodes). Results are presented on the quench heater performance, and on the maximum temperatures and voltages observed during quenches under the so-called 'machine conditions'. Moreover, an update of the quench simulation package specially developed at CERN (QUABER 2) has been recently made. Details on this new version of QUABER are given. Simulation runs have been made specifically to validate the model with the results from the measurements on quench protection mentioned above.

Tests have been carried out on a string of prototype superconducting magnets, consisting of one double-quadrupole and two double-dipoles forming the major part of a half-cell of the LHC machine. The magnets are protected individually by 'cold diodes' and quench heaters. The electrical aspects of these tests are described here. The performance during quench of the protection diodes and the associated interconnections was studied. Tests determined the magnet quench performance in training and at different ramp-rates, and investigated the inter-magnet propagation of quenches. Current lead and inter-magnet contact resistances were controlled and the performance of the power converter and the dump switches assessed.

High field superconducting magnets working at superfluid helium temperature are requested for the 7 TeV LHC accelerator. Several single and twin aperture 1 m long dipole models were measured to compare the differences in behaviour due to design and fabrication. They are shown to be valid models to predict the behaviour of full length magnets. The analysis of the numerous data collected during the performance tests of these magnets allows the proposal of some guidelines to understand the causes of the training quenches. Short sample measurements of both single strands and cables are compared with ultimate field values obtained on the magnets.

The results of cryogenic, mechanical, pressure and electrical tests on two twin-aperture quadrupole prototypes designed for the Large Hadron Collider are presented. The superconducting magnets, which were built by the European Organization for Nuclear Research and France's CEA Saclay, were tested in their powering, ramping, cool-down, stand-by, quenching and warming-up states. Based on the results, the two quadrupoles can attain a nominal current of 15,060 A with 'little training.'

The quench protection system for the superconducting magnets of the CERN Large Hadron Collider (LHC) is described. The system is based on the so called 'cold diode' concept. In a group of series connected magnets if one magnet quenches then the magnetic energy of all the magnets will be dissipated in the quenched magnet so destroying it. This is avoided by by-passing the quenched magnet and then rapidly de-exciting the unquenched magnets. For the LHC machine it is foreseen to use silicon diodes situated inside the cryostat as by-pass elements - so called 'cold diodes'. The diodes are exposed to some 50 kGray of radiation during a 10 year operation life-time. The high energy density of the LHC magnets (500 kJ/m) coupled with the relatively slow propagation speed of a 'natural' quench (10 to 20 m/s) can lead to excessive heating of the zone where the quench started and to high internal voltages. It is therefore necessary to detect quickly the incipient quench and fire strip heaters which spread the quench out more quickly over a large volume of the magnet. After a quench the magnet chain must be de-excited rapidly to avoid spreading the quench to other magnets and over-heating the by-pass diode. This is done by switching high-power energy-dump resistors in series with the magnets. The LHC main ring magnet will be divided into 16 electrically separated units which has important advantages.

The results of tests made on twin-aperture dipole magnets are presented. The 1-m long accelerator type superconducting magnets, which were developed for the European Laboratory for Nuclear Research's large hadron collider, generates a 10-T magnetic field in its 50-mm diameter bore. Built to evaluate various designs, the magnets have different electrical insulation and superconducting cables. Their characterization covers electrical and mechanical performances.