High Energy Physics has been consistently pushing the performance of technical superconductors, for the benefit of high field magnet technology. So far the workhorse for particle accelerators has ...been Nb-Ti, but the practical performance limit has been attained with the LHC. Calls for higher beam luminosity (e.g., HL-LHC), and higher beam energy (e.g., FCC), demand a transition from Nb-Ti to Nb 3 Sn, presently the only practical candidate material offering the required high field performance. This paper provides a summary of desirable properties and performance targets for Nb 3 Sn to satisfy the challenging magnet specifications for upgrades of existing and future HEP accelerators.
Since its discovery in 2001, MgB2 has generated interest for practical applications. Its availability in the form of multifilamentary round wire makes it suitable for production of cables. Together ...with relatively high critical temperature and potential low-cost, this renders it appealing for use in superconducting devices where its limited in-field performance can be tolerated. The state-of-the-art properties of commercially available wire and the potential of MgB2 conductors for use in superconducting systems are discussed. An overview of high-current electrical transmission projects where MgB2 has been proposed as an alternative to conventional Nb-Ti or High Temperature Superconductors is presented.
Large-capacity current leads Ballarino, A.
Physica. C, Superconductivity,
09/2008, Letnik:
468, Številka:
15
Journal Article, Conference Proceeding
Recenzirano
Odprti dostop
Feeding superconducting magnets with reliable low-loss devices is a key issue for any cryo-electrical system. Conventional or HTS current leads can be used, and cooling methods, materials, and ...geometries can be chosen to optimize the thermo-electrical performance of the system. The LHC magnets are powered via more than 3000 current leads transporting altogether about 3
MA of current. With thousands of leads, the LHC lead project represents today the largest project of its kind ever undertaken. Following a review of the LHC lead project, an overview of the choices that can be made for the optimization of large capacity current leads is presented. Examples are given of other leads for large scale magnet systems for which the use of HTS is being envisaged.
The powering of the LHC machine relies on more than 3000 current leads transferring all together about 3 MA of current from/to the superconducting magnets. Among these leads, more than 1000 are based ...on high-temperature superconducting material. This paper reports on the experience gained after the first 3 years of operation in a real accelerator environment, where the leads underwent the thermal and electrical cycles required for the operation of the machine. Faulty conditions experienced during operation are also reported.
A novel quench detection technique for superconducting power cables is proposed. The basic idea relies on the concept of probing a resistance build up through the injection of a small current in ...parallel to the operating cable. Using a well-designed current comparator circuit, the quench process is detected by means of a current measurement. Issues related to noise interferences are mitigated by introducing a differential detection schema. The effectiveness of the approach is shown by implementing a first proof-of-concept device. Experimental results from measurements carried out on MgB2 superconducting cables, at the SM18 test facility at CERN, show the capabilities of the system to properly detect a quench.
In the framework of the High Field Magnets program at CERN, lower limits of degradative mechanical loads on reacted and impregnated Nb 3 Sn Rutherford-type cables are being studied with the goal of ...optimizing the pre-stress applied at room temperature on the accelerator magnets. Coils are loaded during assembly, for instance when transverse load is applied by using a collaring press or the bladder and key technique. Nb 3 Sn is susceptible to transverse compressive stress, which is the loading condition investigated for this study. The purpose of this work is to identify the maximum pressure that can be applied, at room temperature, to reacted cables without generating cracks in the Nb 3 Sn subelements and to quantify the crack propagation with increasing pressure. Metallographic techniques are used to examine the onset and evolution of damage in the transverse planes of impregnated double-stacked Rutherford-type cable specimens with increasing stress. The damage pattern observed at subelement, strand and cable levels is described. Two reaction heat treatment cycles are analyzed.
A number of physics experiments call for the use of iron-dominated, normal-conducting electromagnets to produce moderate fields (2 T range) in a large gap or over a large volume. Although robust and ...reliable, these magnets require significant electrical power, in the MW range, and can thus be costly to operate, especially in DC mode. We report on the design and test of a superconducting, proof-of-principle demonstrator that makes use of technological developments carried out for the High Luminosity upgrade of the Large Hadron Collider at CERN (HL-LHC). The demonstrator includes a superconducting coil, wound from a MgB 2 cable, and mounted inside an iron yoke with a 62 mm gap. As a first phase, the demonstrator was successfully tested in liquid helium at 4.5 K, generating a magnetic flux density of 1.95 T at a current of 5 kA. In a second phase, currently under preparation, the demonstrator will be tested in gaseous helium at 20 K. The design concepts of the demonstrator can be scaled up to large, iron-dominated electromagnets.
High temperature superconductors (HTS) in the form of REBCO (RE 1 Ba 2 Cu 3 O 7-δ ) coated conductor tapes have undergone, in recent years, major improvement of their transport current properties in ...high magnetic fields and at liquid helium temperature. The modelling of coils and other applications using REBCO tapes requires accurate characterization and precise knowledge of their properties. In this paper, we report on an anisotropic scaling law that describes the field dependence of the critical current of REBCO tapes up to the irreversibility field, <inline-formula><tex-math notation="LaTeX">{{{\bm{B}}}_{{\bm{irr}}}</tex-math></inline-formula>, and at temperatures of up to the critical temperature, <inline-formula><tex-math notation="LaTeX">{{{\bm{T}}}_{\bm{c}}}</tex-math></inline-formula>. We performed an experimental campaign to investigate the properties of recently produced commercial tapes and verify the validity of the scaling law. We measured the magnetic field dependence of the critical current in liquid helium at 4.2 K and in applied perpendicular fields of up to 15 T. The experimental setup allowed the characterization of the <inline-formula><tex-math notation="LaTeX">{{{\bm{I}}}_{\bm{c}}}</tex-math></inline-formula> of tapes up to 2.6 kA. Magnetization measurements were also used to complement the transport measurements for temperatures in the range from 4.2 K up to close to <inline-formula><tex-math notation="LaTeX">{{{\bm{T}}}_{\bm{c}}}</tex-math></inline-formula> and in background fields of up to 10.5 T.
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