The Large Hadron Collider (LHC), the particle accelerator at CERN, Geneva, is the largest and probably the most complex scientific instrument ever built. Superconductivity plays a key role because the accelerator is based on the reliable operation of almost 10?000 superconducting magnets cooled by 130 tonnes of helium at 1.9 and 4.2?K and containing a total stored magnetic energy of about 15?000?MJ (including detector magnets). The characteristics of the 1200 tonnes of high quality Nb?Ti cables have met the severe requests in terms of critical currents, magnetization and inter-strand resistance; the magnets are built with an unprecedented uniformity, about 0.01% of variation in field quality among the 1232 main dipoles, which are 15?m in length and 30 tonnes in weight. The results of this 20-year-long enterprise will be discussed together with problems faced during construction and commissioning and their remedies. Particular reference is made to the severe incident which occurred nine days after the spectacular start-up of the machine on 10 September 2008. The status of repair and the plan for the physics programme in 2010 are also presented.

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Superconductivity: its role, its success and its setbacks in the Large Hadron Collider of CERN

NbTi superconductors with low ac loss: A review

Six contracts have been placed with industrial companies for the production of 1200 tons of the superconducting (SC) cables needed for the main dipoles and quadrupoles of the Large Hadron Collider (LHC). In addition, two contracts have been placed for the supply of 470 tons of NbTi and 26 tons of Nb sheets. The main characteristic of the specification is that it is functional. This means that the physical, mechanical and electrical properties of strands and cables are specified without defining the manufacturing processes. Facilities for the high precision measurements of the wire and cable properties have been implemented at CERN, such as strand and cable critical current, copper to superconductor ratio, interstrand resistance, magnetization, RRR at 4.2 K and 1.9 K. The production has started showing that the highly demanding specifications can be fulfilled. This paper reviews the organization of the contracts, the test facilities installed at CERN, the various types of measurements and the results of the main physical properties obtained on the first batches. The status of the deliveries is presented.

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Status of the LHC superconducting cable mass production

In the LHC main magnets, using Rutherford type cable, the eddy current loss and dynamic magnetic field error depend largely on the electrical resistance between crossing (Rc) and adjacent (Ra) strands. Cables made of strands with pre-selected coatings have been studied at low temperature using a DC electrical method. The significance of the inter-strand contact is explained. The properties of resistive barriers, the DC method used for the resistance measurement on the cable, and sample preparation are described. Finally the resistances are presented under various conditions, and the effect is discussed that the cable treatment has on the contact resistance.

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DC measurement of electrical contacts between strands in superconducting cables for the LHC main magnets

In the years 2009–2013 the Large Hadron Collider (LHC) has been operated with the top beam energies of 3.5 and 4 TeV per proton (from 2012) instead of the nominal 7 TeV. The currents in the superconducting magnets were reduced accordingly. To date only seventeen beam-induced quenches have occurred; eight of them during specially designed quench tests, the others during injection. There has not been a single beam-induced quench during normal collider operation with stored beam. The conditions, however, are expected to become much more challenging after the long LHC shutdown. The magnets will be operating at near nominal currents, and in the presence of high energy and high intensity beams with a stored energy of up to 362 MJ per beam. In this paper we summarize our efforts to understand the quench levels of LHC superconducting magnets. We describe beam-loss events and dedicated experiments with beam, as well as the simulation methods used to reproduce the observable signals. The simulated energy deposition in the coils is compared to the quench levels predicted by electrothermal models, thus allowing one to validate and improve the models which are used to set beam-dump thresholds on beam-loss monitors for run 2.

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Testing Beam-Induced Quench Levels of LHC Superconducting Magnets

The contact resistance between crossing strands of Rutherford type superconducting be an essential parameter the main magnets in accelerators like the LHC. A strong development program to study the parameters fixing its value has been launched at CERN. The electrical contact resistance of individual strands with pre-selected coatings has been studied at 4.2 K under varying loading force by means of a 3 contacts DC method. The electro-mechanical properties of contacts have been studied on bare strands and strands with Sn, Ni, or Zn based coatings. The contact resistances measured on strands were compared to measurements made on cables. Contact resistance properties were analysed with respect to the requirements for the LHC main magnet cables.

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Examination of contacts between strands by electrical measurement and topographical analysis

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J.-M. Depond

Papers

DC measurement of electrical contacts between strands in superconducting cables for the LHC main magnets

Examination of contacts between strands by electrical measurement and topographical analysis

Superconducting cable topology