1.1 Team members
2 Physics of HTS
3 HTS materials
4 HTS leads
5 Resistive leads
6 Other activities
The powering of the LHC
superconducting magnets will be made via 3250 current leads transporting in total
about 3 MA of current into the “cold-mass” of the LHC machine. They
will be installed in the LHC tunnel, where they will provide the electrical link between the room temperature
power cables and
the cold bus-bars, bringing the current from/to the cryo-magnets.
Following an intensive R&D program, which started at CERN in early 1995, devoted to the test of high current HTS elements, the Bi-2223 tape with a silver-gold alloy matrix has been selected as the most suitable material for the LHC current lead application. The HTS current leads for the LHC machine represent the first application of HTS material in a large scale accelerator system.
current leads are used for circuits operating at ultimate currents comprised
in the range 600
A to13000 A. They are designed as three different types optimized for operating respectively at 600 A,
6000 A and 13000 A. They power the LHC main dipole and quadrupole
magnets, the dipole and quadrupole magnets in the matching sections and
dispersion suppressors and some of the
Mandate of the AT-MEL-CF section
Since the discovery of High Temperature Superconductivity in lanthanum copper oxides, discovery marked by the award of the Nobel prize to Bednorz and Muller in 1987, no generally accepted microscopic theory for the mechanism responsible for the superconductivity in High Temperature Superconductors (HTS) has been formulated. After the lanthanum-barium-copper oxide superconductors (La2-xBaxCuO4), having a critical temperature of about 30 K, other materials belonging to the same cuprate family were found to be superconducting at even higher temperatures: the yttrium-barium-copper-oxide superconductors YBa2Cu3O7, with a critical temperature of 92 K, the bismuth-strontium-calcium-barium oxide superconductors Bi2Sr2Ca2Cu3O10 and Bi2Sr2CaCu2O8, with a critical temperature of 110 K and 85 K respectively and the thallium-barium-calcium oxide superconductors Tl2Ba2Ca2Cu3O10, with a critical temperature of 125 K. All these materials have as common feature a crystal structure that includes layers of copper-oxygen planes, through which the superconducting current flows.
In the BCS quantum-mechanical theory of conventional superconductors, the electron flux consists of bound pairs of electrons. The pairing is caused by an attractive force between electrons. The electrons are bound in Cooper pairs by an electron-phonon interaction, i.e. by phonon-mediated pairing. The electron's wave function that describes the pair is spherical, indicating that the chance of finding one carrier in a Cooper pair given the position of the other falls off at the same exponential rate in all directions in space. This pairing is said to have s-wave symmetry.
The HTS superconductors display many of the well-known properties of conventional superconductors, such as Josephson tunneling, vortex structure, type II behavior and Meissner effect. However, they also have properties that are unusual for BCS-like materials. Some of these are their high critical temperature, their linear dc resistivity in the normal state and their extremely small coherence length, which is comparable to the grain boundary thickness and therefore makes the weak-link behavior a real problem for transport properties. In addition, HTS are characterized by a large spatial anisotropy, which is due to their layered crystal structure. These layers are composed of Cu-O planes, separated from each other by planes of other oxides and rare earths. It is believed that superconductivity and charge transport are mostly confined in the Cu-O planes, called the ab planes, perpendicular to the c axis. This structural anisotropy translates into anisotropy of most physical properties.
While it is admitted that there is some electron pairing mechanism involved in high temperature superconductivity, the nature of the pairing mechanism is not yet understood. It is considered that the pairing interaction may not be phonon-mediated and may not be the same for all HTS superconductors. Lattice vibrations alone are not strong enough to maintain electron pairing at elevated temperatures. Pairing mechanisms of magnetic origin have been proposed, mainly to justify the high critical temperatures of HTS: the magnetic exchange energies are about four times the phonon energies. In this case, the electron pairing would have a wave function with d-wave symmetry. The d-state appears as a four lobes lying in a plane, like a four-leaf clover. One of the most dominant theories that contains d-wave symmetry is the spin wave model. According to this theory, the carrier leaves a magnetic disturbance (a spin wave) in its wake. This wake pulls a second carrier, so that the two forms a Cooper pair. The spin waves are short-lived, so they are often called spin fluctuations. However, some measurements are in apparent contradiction with this picture. For instance, results of Josephson tunneling experiments are an argument for the paired electrons being in a spin-singlet s-state. It was pointed out that Josephson tunneling should not be possible between paired electrons in two different superconductors unless they have the same symmetry. The Josephson tunneling experiment between yttrium-barium-copper-oxide superconductors and a Pb/Sn (an ordinary s-wave superconductor) point contact, would be in favor of paired electrons in a s-state. Also, the temperature-dependent penetration-depth for HTS gives weight to the argument that these materials are s-wave. Phonon mediated pairing would be consistent with the experimentally observed s-state pairing.
For the electron pairing mechanism, other quasiparticles such as antiferromagnetic magnons or excitons have also been proposed as pairing intermediates. Alternatively, other mixed mechanisms have been considered, like a phonon-mediated mechanism with some sort of a booster to increase the critical temperature of the superconductor.
The MgB2 superconductor, discovered in 2001 by a team of Japanese researchers, does not belong to the family of cuprates. This superconductor, with a critical temperature of 39 K, is not a copper oxide: it is a much simpler compound that seems to represent a whole new superconductor family, more than being simply a Low Temperature Superconductor (LTS) with an unusually high critical temperature. The large isotope effect found in this superconductor confirms the key role of electron-phonon coupling. However, the electronic structure in MgB2 is such that there are two types of electrons at the Fermi level, one of them being much more strongly superconducting than the other. This is in contrast with the theory of phonon mediated superconductivity, which assumes that all the electrons behave in the same manner.
It is certainly true that the HTS field is still young and it evolves rapidly. It is also true that it took 45 years after the discovery of superconductivity in solid mercury at 4.2 K -by Kamerlingh Onnes in 1911- to arrive at a solid understanding of conventional superconductors through the microscopic BCS theory. While some practical HTS superconductors are now being made and some applications are appearing, it is felt that it may still be a long time before the physics of HTS is fully understood and explained in one -or more- theories enjoying consensus among theoretical physicists. Progress in the field has been, up to now, mainly driven by experimental work. Finding a theory would probably help researchers to address some of the problems encountered when working with this new generation of superconductors.
HTS materials have already been used to demonstrate a variety of applications. In the field of large-scale applications, where high currents and long lengths are required, power transmission cables, fault current limiters, transformers, motors and generators have been made using both 1st and 2nd generation HTS. For small-scale applications, where more specialized properties of HTS tend to be used, examples are detection systems and analog and digital processing.
Different type of materials are commercially available today:
Bi-2223 (Bi2Sr2Ca2Cu2Ox) multi-filamentary tape (1st generation superconductor). This material is available on the market in long (about 1 km) lengths. The tape, which is typically about 4 mm wide and 0.2 mm thick, is produced with the Powder In Tube (PIT) process. It has a silver alloy matrix, which is reinforced either by alloying or by attachment to a metallic substrate to improve its strength tolerance.
Bi-2212 (Bi2Sr2CaCu2Ox) multi-filamentary wire and tape (1st generation superconductor). It is also available in long lengths. Having a high critical field, it is particulary suited for high current or high field applications at temperatures below 20 K, such as inserts in high field magnets.
Y-123 (YBa2Cu3O7-x) coated conductors (2nd generation superconductor), where a bi-axially textured superconductor is coated on a flexible ribbon. This material is in these days becoming available on the market in lengths of about 100 meters. It is expected to replace the Bi-2223 because of its higher critical temperature and field and the lower cost of raw materials.
Bulk melt-textured Y-123 and melt-cast processed Bi-2212 materials for novel applications such as magnetic bearings, magnetic shields, flywheels and current limiters.
MgB2 in the form of bulk, tape and wire. It can be produced either with in-situ (reaction between Mg and B) or ex-situ (sintering of MgB2 powders) processes. It has a relatively low critical temperature (39 K), but a high potential in view of the low cost of raw materials and manufacturing processes. It is becoming available in long lengths in the form of wire and tape.
In the LHC we take advantage of the unique properties of the HTS material to reduce considerably the heat in-leak via the current leads. Stacks of Bi-2223 tape in a silver-gold matrix are used to feed more than 3 MA of current to the superconducting magnets operating at liquid helium temperature. The LHC current leads, which represent the first application of HTS material for accelerator technology, provide a unique opportunity to demonstrate the value of incorporating HTS materials into a large scale system
As part of an intensive R&D program which started in early 1995 and ended in 2002, a full range of HTS materials were studied and tested at CERN. The scope of this work was to verify their current capability at temperatures of up to 77 K, their suitability for reproducible low resistance and high current joints, their behavior in case of resistive transition and their thermal performance. These materials, tested either in the form of samples or integrated in prototype current leads, were: Bi-2223 tape with various percentage of Au in the Ag matrix, DIP coated Bi-2212, Melt Cast Processed Bi-2212, Accordion Folding Method Bi-2223, Melt Textured Y-123, Ceramo Crystal Growth Y-123 and Laser Floating Zone Bi-2212.
In view of its good thermal and electrical performance and established quality control procedures associated with industrial scale production, the Bi-2223 tape was identified as being the most suitable material for application to the LHC HTS current leads.
Bi-2223 tape and Bi-2223 stacks
Thirty-one kilometers of Bi-2223 tape were purchased from two manufactures (AMSC and EAS). The tape was specified to have superconducting filaments- (Bi,Pb)2Sr2Ca2Cu3OX, X » 10- embedded in a silver alloy matrix doped with gold. The percentage of gold in the matrix is in the range from 4 to 5.3 weight percentage. The tape, 4 mm wide and 0.2 mm thick, was delivered in spools having a minimum length of 100 metres. The measured average critical current of the spools, at 77 K and in self-field, is about 100 A.
The Bi-2223 tape is integrated in the current leads in form of stacks. A number of five to nine tapes are vacuum soldered together to form a comparatively rugged conductor transporting, at 77 K and in self-field, a current between 350 A and 600 A. This activity of vacuum soldering of the tapes into stacks is performed at CERN: the tape is inspected, cut to the required length, assembled into appropriate moulds and vacuum soldered in the CERN vacuum soldering facilities. About 10000 HTS stacks are being manufactured at CERN for integration in the LHC current leads. As part of the quality control program, all stacks are characterized in liquid nitrogen and in self-field. The n-exponent value of the stacks, calculated as the slope of the logarithmic plot of the voltage versus current in the range from 0.1 mV/cm to 2 mV/cm, is about 20. For all stacks, the critical current is measured for electric fields of 0.1 mV/cm, 1 mV/cm and 2.5 mV/cm.
For full traceability, the spool and the stack characteristics and their characterization curves are stored in a database, together with the information related to the current lead and to the LHC magnet circuit powered by the leads.
Some stacks, representative of each different type integrated in the current leads, underwent a full characterization at 77 K and 65 K in magnetic fields, parallel and perpendicular to stacks, of up to 0.5 T.
Short samples of Bi-2223 tape underwent tests of irradiation by fast neutrons both at room and liquid nitrogen temperatures. It was found that integrated doses of up to 5.10-15 cm-2 , equivalent to about 500 kGy, do not give rise to significant degradation of the critical current of the tape.
To prevent "bubbling" of the stacks, which will be exposed during the LHC operation to liquid helium and cold helium gas, a coating procedure has been proposed and validated by CERN. It consists in the vacuum impregnation of the HTS stacks with a thin layer of the polymer poly-para-xylene (ParyleneÒ). The vacuum impregnation takes place at room temperature on the stacks already assembled on the supporting structure that is part of the current lead assembly.
The LHC will require the transfer of more than 3 MA of current for the powering of the superconducting magnets operating at superfluid helium temperature. About 26 % of this current is transported by leads feeding the main dipole and quadruple magnets (13000 A), 54 % by leads powering the insertion magnets (3400 A-6800 A), 17 % by leads for the corrector magnet circuits (600 A) and the remaining 5 % by leads for the dipole corrector magnets (60 A-120 A). Prior to starting the design of the LHC leads, a study was made to evaluate the exergetic costs of different cooling methods available within the already well-defined infrastructure of the LHC machine, and the potential saving in liquefaction power induced by the use of HTS material. The most convenient solution, finally adopted for all the LHC HTS current leads, consists in cooling the resistive part of the lead with 20 K/1.3 bar helium gas, recovered from the LHC beam screen cooling line, while the HTS element operates in self-cooling conditions between an intermediate temperature (THTS) and the 4.5 K liquid helium bath. The estimated saving in total cooling power with respect to conventional self-cooled current leads, which conduct into the helium bath about 1.1 W/kA, corresponds to 30 % while the heat load into the liquid helium is reduced by a factor greater than 10. These values were confirmed by several measurements performed at CERN on prototype leads. It was decided to integrate HTS material in all the current leads transporting currents ranging from 600 A to 13000 A.
The LHC HTS current leads operate in a temperature range between room temperature and the saturated liquid helium bath. They consist of a resistive section, convection cooled by helium gas available in the LHC machine at a nominal temperature of about 20 K, and a superconducting section, self-cooled by the vapour generated by the lead itself at 4.5 K. The two circuits are hydraulically separated. The warm end of the superconducting section, THTS, is maintained at 70 K in stand-by operation and at 50 K in operation with current. Integrated within the current lead body is the instrumentation required for its operation and protection: a platinum sensor, at the top of the HTS unit, used for the control of the 20 K helium mass flow rate, and the voltage taps which are provided for independent protection of the resistive (100 mV threshold) and HTS part (5 mV threshold). Additional voltage taps are made available for the protection of the magnet circuits.
The detailed design of the leads was made at CERN, where the prototype units were also tested in cryogenic conditions. The leads are grouped in three different series, designed for operating respectively at 13000 A, 6000 A and 600 A.
A pre-series of 140 units was manufactured and assembled at CERN. The complete series of leads is being manufactured in CECOM, Rome, for the 13000 A leads and in the Russian laboratory of BINP, Novosibirsk, for the 6000 A and 600 A current leads, on the basis of CERN "build-to-print" designs. All HTS current leads are measured at maximum current prior to installation in the LHC machine: the laboratory of ENEA, Frascati, measures the series of 13000 A and 6000 A HTS current leads, while the University of Southampton measures the series of 600 A HTS current leads.
The 13000 A and 6000 A current leads are manufactured as single units, while the 600 A current leads are assembled in a group of four on a common insulating flange. The table below summarizes the typical performance of the three different type of leads when operating at maximum current, as already repeatedly measured on hundred of units.
13000 A Heat exchanger
The powering of the LHC close orbit correctors will be made via 1504 current leads rated for a maximum current of 60 A. Additional 520 current leads are needed for the powering of the corrector magnets operating at currents of up to 120 A. At CERN, two different designs were developed for these leads:
· a conduction-cooled design, for all the 60 A leads and for part -324 in total- of the 120 A leads;
· a gas-cooled design for the remaining 120 A current leads.
Conduction-cooled current leads
The conduction-cooled current leads are integrated in the main vacuum insulation of the LHC Short Straight Section (SSS) cryostats. They transport the current from room temperature to the 1.9 K liquid helium bath. In view of their important number and of the strong space constraints imposed by the cryostat configuration, they are assembled in a group of four on a common stainless steel flange. They are pre-shaped as requested by the integration requirements, which require that these leads are the last components to be integrated into the already densely packed LHC cryostats.
An hybrid conductor, electrical insulated via a multilayer Kapton® tube, is first inserted in a thin stainless steel tube and then pre-shaped with a tooling, specially developed at CERN. The four tubes are finally welded to the warm and cold stainless steel flanges. The hybrid conductor is a red brass rod that is copper plated along the entire length with two different copper thickness (thinner in the lower part). This hybrid conductor was chosen in order to minimize the heat load into the helium bath while assuring good stability in case of thermal run-away. The conductors of each assembly are thermalized against two heat sinks that are fixed to two cryogenic lines carrying gas at 50 K-75 K and at 5 K-20 K respectively. The heat sinking at intermediate temperatures is made in order to minimize the heat losses into the liquid helium bath.
The design of these leads is extremely compact. It has the advantage, when compared to conventional self-cooled leads, of not requiring warm valves and pipes for the control and recovery of the helium flow. It avoids the use of cold vacuum-tight ceramic feedthroughs. In addition, thanks to the material choice and to the good design of the heat sinks, the leads have good thermal performance. The calculated losses into the helium bath of the a 60 A current leads are < 90 mW at 15 A, which is the average current estimated for these corrector magnets, and 170 mW at maximum current. For comparison, a conventional conduction-cooled current lead operating at 60 A would conduct about 2.5 W into the bath. The predicted thermal and electrical performance of the 60 A current leads have been confirmed by precise measurements performed on series components integrated in a ad-hoc cryostat built in the University of Southampton.
The series production on the 60 A and 120 A conduction-cooled current leads is being manufactured on the basis of a CERN "build-to-print" design respectively in Mark&Wedell, Copenhagen, and in CECOM, Rome.
Gas-cooled current leads
The gas-cooled current leads are integrated in cryostats, located in the insertion regions of the LHC machine, which house also the HTS current leads. They transport the current from room temperature to the 4.5 K liquid helium bath. The design is very compact. Depending on the requirements of the powering, the leads are assembled in groups of four or eight on a common supporting flange. The novelty of this design with respect to conventional self-cooled current leads consists in extracting the heat from the leads of the same assembly via common heat exchangers, cooled by the gas produced by the thermal conduction of the leads themselves at 4.5 K. This solution has two important advantages: the reduction in the number of valves needed for the cooling of the leads from one per lead to one per lead assembly, with significant economical savings in particular in view of the important number of leads, and the compactness of the design, which is made possible also by the simplification of the cooling scheme. The thermal performance of these leads is comparable to the one of conventional self-cooled current leads optimized for the same current rating.
gas-cooled current lead assembly (8 leads)
As part of the laboratory activity, assembly work and different types of measurements are performed within the AT-MEL-CF section. The latter include both series measurements on the current leads that are carefully checked prior to integration in the LHC tunnel - leak tightness, high voltage electrical insulation and instrumentation tests - and measurements on different type of materials to verify their thermal and electrical properties at cryogenic temperatures. In particular, the following measurements are performed:
RRR (Residual Resistivity Ratio) measurements;
Thermal conductivity measurements in the range from 50 K to 4.2 K;
Critical current measurements of HTS materials at liquid helium and liquid nitrogen temperatures.
The section is also in charge of the specification, procurement and supply of the electrical equipment needed for the operation of the current leads in the LHC tunnel. This is the equipment required for the powering and control of the cartridge heaters integrated at the top of the leads to avoid condensation in stand-by conditions and includes more than a thousand of isolation transformers, heaters and heater control units and kilometers of power and instrumentation cables.
While the conception, the optimization and the detailed design of the LHC leads was made at CERN, where prototypes of each type of current lead were built and tested, the series production of the components is being carried out in companies and external laboratories on the basis of the CERN specifications and drawings. The electrical characterization at cryogenic temperatures of the series of HTS leads is also made by external laboratories.
In addition to the above listed contracts and collaboration agreements, some activities related to the current leads project are performed in-house. These activities are:
Test in Southampton of 600 A current leads
List of main publications
First Test of Twisted-Pair HTS 1 kA Range Cables for Use in Superconducting Links, Proceedings of EUCAS 2011
First Electrical Characterization of Prototype 600 A HTS Twisted-Pair Cables at Different Temperatures, Proceedings of EUCAS 2011
Design of the HTS Current Leads for ITER, Proceedings of MT-22 (2011)
Alternative Design Concepts for Multi-Circuit HTS Link Systems, A. Ballarino, ASC 2010, IEEE Transactions on Applied Superconductivity, Vol. 21, No.3, June 2011
Design of an MgB2 Feeder System to Connect Groups of Superconducting Magnets to Remote Power Converters, A. Ballarino, EUCAS 2009, Journal of Physics: Conference Series 234 (2010) 032003
Scaling of Superconducting Switches for Extraction of Magnetic Energy, A. Ballarino and T. Taylor, IEEE Transactions on Applied Superconductivity, Vol. 20, No.3, June 2010
Conceptual Design of the LHC Interaction Region Upgrade - Phase I,
The LHC upgrade team, LHC Project Report 1163, CERN,
Power Switches utilizing Superconducting Material for Accelerator Magnets, S. A. March, A. Ballarino, Y. Yang, ASC 2008, Chicago
Commissioning of the LHC Current Leads, A. Ballarino, S. A. March, K. H. Meb, EPAC 2008, Genova
Performance of the Superconducting Corrector Magnet Circuits during the Commissioning of the LHC, The LHC commissioning team, EPAC 2008, Genova
Large-Capacity Current Leads, A. Ballarino, ISS 2007, Tsukuba
Extending the use of HTS to Feeders in Superconducting Magnet Systems, A. Ballarino, K. H. Meb, T. Taylor, MT-20 2007, Philadelphia
Toward the Design of Power Switches utilizing HTS Material, S. A. March, A. Ballarino, C. Beduz, K. H. Meb, Y.Yang, EUCAS 2007, Brussels
Extending the Application of HTS in Particle Accelerators, A. Ballarino, K. H. Meb, T. Taylor, EUCAS 2007, Brussels
Quench Characteristics of Ag/AuBi2223 HTS-stainless steel stack used for the Hybrid Current Leads of the Large Hadron Collider, M. K. Al-Mosawi, S. Avgeros, C. Beduz, Y. Yang and A. Ballarino, EUCAS 2007, Brussels
HTS Current Leads: Performance Overview in Different Operating Modes, A. Ballarino, ASC 2006, IEEE Transactions on Applied Superconductivity, Vol.17, No. 2, June 2007
The Commissioning of the LHC Technical Systems, The LHC Hardware Commissioning Team, Proceedings of PAC 2007
Large Scale Assembly and Characterization of Bi-2223 HTS Conductors, A. Ballarino, L. Martini, S. Mathot, T. Taylor and R. Brambilla, Proceedings of ASC 2006, August 2006, Seattle
Full Cryogenic Test of 600 A HTS Hybrid Current Leads for the LHC, M.K. Al-Mosawi, S.A. March, C. Beduz, A. Ballarino and Y. Yang, Proceedings of ASC 2006, August 2006, Seattle
Cryogenic Test of High Temperature Superconducting Current Leads at ENEA, Advances in Cryogenic Engineering: Transactions of the Cryogenic Engineering Conference, Vol. 51, 2006
DC and AC Electrical Characterization of Stacks of HTS Tapes, S. Ginocchio, A. Ballarino, E. Perini, S. Zanella, Proceedings of ASC 2006, August 2006, Seattle
HTS in the LHC & in the LHC Upgrades, A. Ballarino, WAMDO Workshop, CERN, April 2006
Conduction-cooled 60 A resistive current leads for the LHC dipole correctors, A. Ballarino, LHC Project Report 691, March 2004
13000 A HTS Current Leads for the LHC Accelerator: from Conceptual Design to Prototype Validation, A.Ballarino, S.Mathot, D.Milani, Proceedings of EUCAS 2003, September 2003, Sorrento, Italy
Effect of fast neutron irradiation on transport properties of HTS materials, T.Taylor, A.Ballarino, A. Ryazanov et al, Proceedings of EUCAS 2003, September 2003, Sorrento, Italy
First Results and Status of the LHC String 2, The String 2 Team, Proceedings of EPAC 2002
HTS Current Leads for the LHC Magnet Powering System, A.Ballarino, Physica C 372-376 (2002) 1413-1418, Invited Paper at the EUCAS 2001 Conference, August 2001, Lyngby, Denmark
Current Leads for the LHC Magnet System, A.Ballarino, Invited Paper at the 17th International Conference on Magnet Technology, 24-28 September 2001, Geneva, Switzerland
Application of High Temperature Superconductors to Accelerators, A.Ballarino, Invited Paper at the Seventh European Particle Accelerator Conference, 26-30 June 2000, Vienna, Austria
High Temperature Superconducting Current Leads for the Large Hadron Collider, A.Ballarino, Presented at 4th European Conference on Applied Superconductivity, Sitges, Spain, September 1999, LHC Project Report 337
120 A Current Leads for the DFBs, A.Ballarino, Engineering Specification, LHC Project Document No. LHC-DFL-ES-0002,January 2005
LHC HTS Current Leads, A.Ballarino, Functional Specification, LHC Project Document No. LHC-DFL-ES-0001,July 2003
IT-2901/AT/LHC, A.Ballarino, Technical Specification for the Manufacture and Supply of Assemblies of 60 A Resistive Current Leads for the LHC Dipole Corrector Magnets, LHC Project Document No. LHC-DFLD-CI-0001, June 2002
IT-3143/AT/LHC, A.Ballarino, Technical Specification for the Manufacture and Supply of HTS BSCCO 2223 Ag-Au Tape, LHC Project Document No. LHC-DFLHT-CI-0001, March 2003
IT-3168/AT/LHC, A.Ballarino, Technical Specification for the Manufacture and Supply of 13000 A HTS Current Leads, LHC Project Document No. LHC-DFLA-CI-0001, September 2003
IT-3303/AT/LHC, A.Ballarino, Technical Specification for the Cryogenic Testing of HTS Current Leads, LHC Project Document No. LHC-DFL-CI-0005, March 2004
IT-600A, A.Ballarino, Technical Specification for the Manufacture and Supply of assemblies of 600 A HTS Current Leads, LHC Project Document No. LHC-DFLB-CI-0001, June 2004
IT-6000A, A.Ballarino, Technical Specification for the Manufacture and Supply of 6000 A HTS Current Leads, LHC Project Document No. LHC-DFLC-CI-0002, June 2004
DO-21889, A.Ballarino, Technical Specification for the Manufacture and Supply of Assemblies of 120 A Current Leads for the LHC Dipole Corrector Magnets, LHC Project Document No. LHC-DFL-CI-0001, May 2004