For the Next European Dipole (NED) program, a Powder-In-Tube (PIT) strand was successfully developed by SMI. This high-performance Nb 3 Sn strand presents a non-copper critical current density of ~ ...2500 A/mm 2 at 12 T applied field and 4.2 K and a filament diameter around 50 mum. Extensive heat treatment optimization studies were performed in order to maximize both critical current and RRR, with a plateau temperature down to 625degC and duration up to 400 hours. It appears that a critical current enhancement of ~ 10% can be achieved for a reaction schedule of 320 hours at 625degC with non-copper critical current density respectively exceeding 2700 and 1500 A/mm 2 at 12 and 15 T (4.2 K). Thanks to this modified heat treatment, this strand completely fulfills the NED stringent specification.
The formation of coarse Nb 3 Sn grains in Internal Tin (IT) strands has been studied at the example of a prototype strand with high Sn content. Metallographic examination revealed that the ...comparatively low critical current density (J c ) of this strand is partly due to the formation of a significant fraction of coarse grained Nb 3 Sn at the periphery of the individual filaments within the subelements. The phase evolution during the reaction heat treatment has been determined in situ by high energy synchrotron X-ray diffraction as well as ex situ by Energy Dispersive X-ray Spectroscopy in a Scanning Electron Microscope (SEM) in order to identify the conditions under which the coarse grains form. Similar to what is observed in the tubular type strands, Nb 3 Sn coarse grain formation occurs in the filament areas that had first been transformed into NbSn 2 and Nb 6 Sn 5 , prior to Nb 3 Sn formation, and it accounts for an estimated Jc reduction of roughly 20%. The amount of Cu-Nb-Sn and NbSn 2 that is formed during the heat treatment can be reduced by increasing the temperature ramp rate, while the amount of Nb 6 Sn 5 formed appears to be hardly influenced by the different heat treatments that have been tested.
The ITER machine will require approximately 250 tons of NbTi strands and 500 tons of Nb 3 Sn strands. NbTi will be used in the Poloidal Field (PF) coils, Correction Coils (CC) and feeder busbars, ...whereas Nb 3 Sn will be used in the Central Solenoid (CS) and Toroidal Field (TF) coils. The large amount of superconducting strands needed requires worldwide procurement, involving suppliers from six of the seven ITER Domestic Agencies (DAs). To ensure reliable test results, it is necessary to benchmark the test facilities at each supplier and at each DA reference laboratory for physical and superconducting properties measurement, as well as sample preparation techniques. Following previous benchmarking efforts related to ITER procurement in the mid-1990's and to supplier and DA laboratory qualification performed on bronze route Nb 3 Sn strands in 2009, we report here the latest rounds on internal tin Nb 3 Sn and NbTi strands. Ten participants from five DAs (China, EU, South Korea, Russia, and the U.S.) together with CERN (the ITER Organisation's reference laboratory) took part in the benchmarking of internal tin Nb 3 Sn strands, and six participants from China and Russia, plus CERN, participated in the benchmarking of NbTi strands.
Strand and Cable R&D for Fast Cycled Magnets at CERN Bottura, L; Bonasia, A; Borgnolutti, F ...
IEEE transactions on applied superconductivity,
06/2011, Letnik:
21, Številka:
3
Journal Article, Conference Proceeding
Recenzirano
Odprti dostop
Fast cycled superconducting magnets (FCM's) are an option of interest for the long-term consolidation and upgrade plan of the LHC accelerator complex. In the past two years we have conducted an R&D ...targeted at investigating the feasibility, operational issues and economical advantage of FCM's in the range of 2 T bore field, continuously cycled at 1 Hz. In this paper we report the main results on the development of strands and cables suitable for this application, providing details on the strands tested and the cable manufacturing and performance.
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.
The degradation mechanisms of state-of-the-art Nb-Ti/Cu superconductors are described, based on in-situ synchrotron X-ray diffraction measurements during heat treatment. A quantitative description of ...the Nb-Ti/Cu degradation in terms of critical current density, Cu stabiliser resistivity and mechanical composite strength is presented. In an applied magnetic field a significant critical current degradation is already observed after a 5-minute 400 °C heat treatment, due to variations of –Ti precipitate size and distribution within the Nb-Ti alloy filaments. A strong degradation of the strand mechanical properties is observed after several minutes heating above 550 °C, which is also the temperature at which the formation of Cu-Ti intermetallic phases is detected. Several minutes heating at 250 °C are sufficient to increase the RRR of the strongly cold work strands inside a Rutherford type cable from about 80 to about 240. Heating for several minutes at 400 °C does not cause a significant conductor degradation in self-field and, thus, leaves enough temperature margin for the electrical interconnection of Nb-Ti/Cu conductors with common low temperature solders.
The next European dipole (NED) activity is aimed at the development of a large-aperture, high-field superconducting magnet relying on high-performances conductors. Part of the NED program is devoted ...to the mechanical study of a new generation of wires and to predict and describe their behavior under the severe loading conditions of the cabling process. A Finite Element modelization of wires was developed, allowing the wire behavior under simple uni-axial loads to be described. In this paper, the mechanical performances of different strand configurations are compared. The external diameter of the wire being fixed, several parameters are taken into account: the total number of sub-elements, the composition of the sub-elements, the local copper-to-non-copper ratio, the number of copper cells in the central region. The aim is to isolate the influence of each parameter on the wire deformations, trying to find an optimum design minimizing cabling damages.
Plans for LHC upgrade and for the final focalization of linear colliders call for large aperture and/or high-performance dipole and quadrupole magnets that may be beyond the reach of conventional ...NbTi magnet technology. The Next European Dipole (NED) activity was launched on January 1st, 2004 to promote the development of high-performance, Nb/sub 3/Sn wires in collaboration with European industry (aiming at a noncopper critical current density of 1500 A/mm/sup 2/ at 4.2 K and 15 T) and to assess the suitability of Nb/sub 3/Sn technology to the next generation of accelerator magnets (aiming at an aperture of 88 mm and a conductor peak field of 15 T). It is integrated within the Collaborated Accelerator Research in Europe (CARE) project, involves seven collaborators, and is partly funded by the European Union. We present here an overview of the NED activity and we report on the status of the various work packages it encompasses.
The High Luminosity (HiLumi) Large Hadron Collider (LHC) project has, as the main objective, to increase the LHC peak luminosity by a factor five and the integrated luminosity by a factor ten. This ...goal will be achieved mainly with a new interaction region layout, which will allow a stronger focusing of the colliding beams. The target will be to reduce the beam size in the interaction points by a factor of two, which requires doubling the aperture of the low-β (or inner triplet) quadrupole magnets. The use of Nb3Sn superconducting material and, as a result, the possibility of operating at magnetic field levels in the windings higher than 11 T will limit the increase in length of these quadrupoles, called MQXF, to acceptable levels. After the initial design phase, where the key parameters were chosen and the magnet's conceptual design finalized, the MQXF project, a joint effort between the U.S. LHC Accelerator Research Program and the Conseil Européen pour la Recherche Nucléaire (CERN), has now entered the construction and test phase of the short models. Concurrently, the preparation for the development of the full-length prototypes has been initiated. This paper will provide an overview of the project status, describing and reporting on the performance of the superconducting material, the lessons learnt during the fabrication of superconducting coils and support structure, and the fine tuning of the magnet design in view of the start of the prototyping phase.
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