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.

/pdf/superconductivity-its-role-its-success-and-its-setbacks-in-3tjozpq7g1.pdf

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

protons/beam. The energy stored in one beam is 350 MJ, more than seven orders of magnitude above the quench limit of a superconducting magnet. After briefly recalling the challenges and design choices of the machine, status and future prospects are discussed.

https://epaper.kek.jp/e02/papers/moxgb003.pdf

Status of the lhc

NbTi superconductors with low ac loss: A review

The main lattice of the Large Hadron Collider (LHC) employs about 1600 main magnets and more than 4000 corrector magnets. All superconducting and working in pressurized superfluid helium bath, these impressive line of magnets fills more than 20 km of the underground tunnel. With almost 70 main dipoles already delivered and 10 main quadrupoles almost completed, we passed the 5% of the production and now all manufacturers have fully entered into series production. In this paper the most critical issues encountered in the ramping up in such a real large scale fabrication is addressed; uniformity of the coil size and of prestress, special welding technique, tolerances on curvature (dipoles) or straightness (quadrupoles) and of the cold mass extremities, harmonic content and, most important, the integrated field uniformity among magnets. The actual limits and the solution for improvements are discussed. Finally a realistic schedule based on actual achievements is presented.

/pdf/superconducting-magnets-for-the-lhc-main-lattice-4kzohcj0ah.pdf

Superconducting magnets for the LHC main lattice

Superconductivity has been the most influential technology in the field of accelerators in the last 30 years. Since the commissioning of the Tevatron, which demonstrated the use and operability of superconductivity on a large scale, superconducting magnets and rf cavities have been at the heart of all new large accelerators. Superconducting magnets have been the invariable choice for large colliders, as well as cyclotrons and large synchrotrons. In spite of the long history of success, superconductivity remains a difficult technology, requires adequate RD it highlights the main characteristics and main achievements, and gives a perspective on the development of superconducting magnets for the future generation of very high energy colliders.

/pdf/superconducting-magnets-for-particle-accelerators-4iny33x9rw.pdf

Superconducting Magnets for Particle Accelerators

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.

/pdf/status-of-the-lhc-superconducting-cable-mass-production-1kht18ndsf.pdf

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.

/pdf/dc-measurement-of-electrical-contacts-between-strands-in-5b04085bib.pdf

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

Putting a resistive core into the center of a Rutherford cable increases resistance between strands in the crossover direction, which greatly reduces the coupling currents, even when the resistance to adjacent turns remains small. This allows one to improve stability by soldering strands together or using porous metal, without incurring a penalty of increased coupling. We describe our manufacturing methods and an experimental measurement of coupling.

/pdf/rutherford-cables-with-anisotropic-transverse-resistance-4086n40pxt.pdf

Rutherford cables with anisotropic transverse resistance

The electrical resistance of contacts between strands in the Rutherford type superconducting cables has a major effect on the eddy current loss in cables, and on the dynamic magnetic field error in the LHC main magnets. In order to guarantee the value and constancy of the contact resistance, various metallic coatings were studied from the electrical and mechanical points of view in the past. We report on the molten bath Sn/sub 95wt/Ag/sub 5wt/ coating, oxidized thermally in air after the cabling is completed, that we adopted for the cables of the LHC main magnets. The value of the contact resistance is determined by the strand coating and cabling procedures, oxidation heat treatment, and the magnet coil curing and handling. Chemical analysis helps to understand the evolution of the contacts. We also mention results on two electrolytic coatings resulting in higher contact resistance.

/pdf/strand-coating-for-the-superconducting-cables-of-the-lhc-3omyqn7cuc.pdf

J.D. Adam

Papers

Status of the LHC superconducting cable mass production

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

Rutherford cables with anisotropic transverse resistance

Strand coating for the superconducting cables of the LHC main magnets