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J. K. Vogel,
F. T. Avignone,
G. Cantatore,
J. M. Carmona,
S. Caspi,
S. A. Cetin,
F. E. Christensen,
A. Dael,
T. Dafni,
M. Davenport, [......], H. H. J. ten Kate,
A. Tomas,
S. Troitsky,
K. van Bibber,
P. Vedrine,
J. A. Villar,
L. Walckiers,
W. Wester,
S. C. Yildiz,
K. Zioutas
[show abstract]
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ABSTRACT: The International Axion Observatory (IAXO) is a next generation axion
helioscope aiming at a sensitivity to the axion-photon coupling of a few
10^{-12} GeV^{-1}, i.e. 1-1.5 orders of magnitude beyond sensitivities achieved
by the currently most sensitive axion helioscope, the CERN Axion Solar
Telescope (CAST). Crucial factors in improving the sensitivity for IAXO are the
increase of the magnetic field volume together with the extensive use of x-ray
focusing optics and low background detectors, innovations already successfully
tested at CAST. Electron-coupled axions invoked to explain the white dwarf
cooling, relic axions, and a large variety of more generic axion-like particles
(ALPs) along with other novel excitations at the low-energy frontier of
elementary particle physics could provide additional physics motivation for
IAXO.
02/2013;
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[show abstract]
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ABSTRACT: The International AXion Observatory (IAXO) will incorporate a new generation
detector for axions, a hypothetical particle, which was postulated to solve one
of the puzzles arising in the standard model of particle physics, namely the
strong CP problem. The new IAXO experiment is aiming at achieving a sensitivity
to the coupling between axions and photons of one order of magnitude beyond the
limits of the current state-of-the-art detector, represented by the CERN Axion
Solar Telescope (CAST). The IAXO detector relies on a high-magnetic field
distributed over a very large volume to convert solar axions into x-ray
photons. Utilizing the designs of the ATLAS barrel and end-cap toroids, a large
superconducting toroidal magnet is currently being designed at CERN to provide
the required magnetic field. The new toroid will be built up from eight, one
meter wide and 20 m long, racetrack coils. The toroid is sized about 4 m in
diameter and 22 m in length. It is designed to realize a peak magnetic field of
5.4 T with a stored energy of 500 MJ. The magnetic field optimization process
to arrive at maximum detector yield is described. In addition, force and stress
calculations are performed to select materials and determine their structure
and sizing. Conductor dimensionality, quench protection and the cryogenic
design are dealt with as well.
12/2012;
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J.Ph. Tock,
F. Bertinelli,
F. Bordry,
P. Fessia,
R. Ostojic,
A. Perin,
H. Prin,
F. Savary,
C. Scheuerlein, H.H.J. ten Kate,
A.P. Verweij,
G.P. Willering
[show abstract]
[hide abstract]
ABSTRACT: Following the incident in one of the main dipole circuits of the Large Hadron Collider (LHC) in September 2008, a detailed analysis of all magnet circuits has been performed by a dedicated task force. This analysis has revealed critical issues in the design of the 13 kA splices between the superconducting dipole and quadrupole magnets. These splices have to be consolidated before increasing the beam energy above 4 TeV and operating the LHC at 6.5-7 TeV per beam. The design of the consolidated 13 kA splices is complete and has been reviewed by an international committee of experts. Also, all other types of superconducting circuits have been thoroughly screened for potential safety issues and several important recommendations were established. They were critically assessed and the resulting actions are presented. In addition to the work on the 13 kA splices, other interventions will be performed during the first long shut-down of the LHC to consolidate globally all superconducting circuits. The associated quality control has been defined. Schedule constraints, repair production rate, available space and resources are presented as well.
05/2012;
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[show abstract]
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ABSTRACT: The new AEGIS (Antimatter Experiment: Gravity, Interferometry, Spectroscopy) Experiment will be installed in the Antiproton Decelerator hall at CERN. The main goal is to measure the Earth's gravitational acceleration of antihydrogen atoms. The experiment consists of two high-homogeneity solenoids placed on the same axis. The 5 T magnet is part of a cylindrical Penning trap to catch and to accumulate antiprotons delivered by the decelerator. The antihydrogen is then produced in the 1 T region where sub-kelvin antiproton temperatures provided by the dilution refrigerator are required to form a slowly-moving beam of antihydrogen. The helium bath cooled superconducting magnets; the different traps and the dilution refrigerator are integrated in a common cryostat with an internal vacuum barrier between the insulating cryogenic vacuum and the very high beam vacuum. In addition, the magnet system has to guarantee a smooth transition between the 5 T and the 1 T magnetic field areas required for a loss-free transfer of antiprotons and positrons from the trapping region to the antihydrogen production area. In this paper the design of this AEGIS magnet system is presented and discussed.
IEEE Transactions on Appiled Superconductivity 07/2011; · 1.04 Impact Factor
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[show abstract]
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ABSTRACT: In the framework of future LHC upgrades using Nb<sub>3</sub>Sn magnets, supported in part by the US LHC Accelerator Research Program (LARP) and the European EuCARD program, CERN is intensifying its research on Nb<sub>3</sub>Sn Rutherford cables. In the FRESCA cable test facility at CERN, two new Nb<sub>3</sub>Sn cable samples were investigated concerning their quench and critical current as well as stability performance. The two samples are based on RRP type strands with comparable layout. They have 27 strands with 0.7 mm diameter while the strands have 54 or 108 superconducting sub-elements. The cables are 10 mm wide and have a transposition pitch of about 75 mm. The cables are used in magnets built for LARP. Their performance is measured as a function of magnetic field up to 10 T with ramp rates of 10 to 1000 A/s and temperature of 1.9 and 4.3 K. A hall probe array is present to study the current distribution. Point heaters are used to study cable stability and current redistribution.
IEEE Transactions on Appiled Superconductivity 07/2011; · 1.04 Impact Factor
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A.P. Verweij,
F. Bertinelli,
N. Lasheras,
Z. Charifoulline,
R. Denz,
P. Fessia,
C. Garion, H.H.J. ten Kate,
M. Koratzinos,
S. Mathot,
A. Perin,
C. Scheuerlein,
S. Sgobba,
J. Steckert,
J.-P. Tock,
G.P. Willering
[show abstract]
[hide abstract]
ABSTRACT: The accident in the LHC in September 2008 occurred in an interconnection between two magnets of the 13 kA dipole circuit. Successive measurements of the resistance of other interconnects revealed other defective joints, even though the SC cables were properly connected. These defective joints are characterized by a poor bonding between the SC cable and the copper stabilizer in combination with an electrical discontinuity in the copper stabilizer. A quench at the 7-13 kA level in such a joint can lead to a fast and unprotected thermal run-away and hence opening of the circuit. It has therefore been decided to operate the LHC at a reduced and safe current of 6 kA corresponding to 3.5 TeV beam energy until all defective joints are repaired. A task force is reviewing the status of all electrical joints in the magnet circuits and preparing for the necessary repairs. The principle solution is to resolder the worst defective joints and, in addition, to apply an electrical shunt made of copper across all joints with sufficient cross-section to guarantee safe 12-13 kA operation at 7-7.5 TeV. In this paper the various actions that have lead to this solution are presented.
IEEE Transactions on Appiled Superconductivity 07/2011; · 1.04 Impact Factor
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[show abstract]
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ABSTRACT: The Nijmegen 45 T hybrid magnet will consist of an inner resistive 33 T resistive magnet and a superconducting 12 T outsert magnet. In the present conceptual design of the layer-wound outsert, the conductor is a Nb<sub>3</sub>Sn-Cu Cable-In-Conduit Conductor (CICC) with a stainless steel conduit, operating at 4.5 K by a forced flow of supercritical helium. At nominal magnetic field, the operating current is 12.3 kA. The outsert magnet design comprises 3 types of CICC design assuming a void fraction of 29 % and a temperature margin above 1.5 K. The design requires for 0.81 mm diameter Nb3 Sn strands a minimum copper fraction of 50% and a minimum equivalent critical current at 12 T, 4.2 K, ?? = 0% of 590 A. A candidate strand considered is a Powder-In-Tube type of NbaSn conductor with 114 filaments and a copper fraction of 55 %. To predict the cable performance in terms of critical current, stability and AC loss under operational conditions to the best of present scaling capabilities, knowledge of the behavior of the critical current I<sub>c</sub>(B, T, ??<sub>axial</sub>), magnetization M(B, dB/dt), stress-strain relation at 300 and 4.5 K and finally I<sub>c</sub> as a function of periodic bending and temperature is required. These essential properties, as measured at the University of Twente employing the TiAIV I<sub>c</sub> barrel, the PacMan and Tarsis strain devices as well as the integrating magnetometer, are presented and discussed.
IEEE Transactions on Appiled Superconductivity 07/2010; · 1.04 Impact Factor
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A. Dudarev, H.H.J. ten Kate,
J. Buskop,
A. Foussat,
P. Benoit,
M. Jeckel,
A. Olyunin,
N. Kopeykin,
V. Stepanov,
L. Deront, [......],
E. Sbrissa,
K. Barth,
J. Bremer,
N. Delruelle,
J. Metselaar,
R. Pengo,
O. Pirotte,
D.E. Baynham,
F.S. Carr,
E. Holtom
[show abstract]
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ABSTRACT: The system of superconducting toroids in the ATLAS experiment at CERN consists of three magnets. The Barrel Toroid was assembled and successfully tested in 2006. Next, two End-Cap Toroids have been tested on surface at 77 K and installed in the cavern, 100-m underground. The End Cap Toroids are based on Al stabilized Nb-Ti/Cu Rutherford cables, arranged in double pancake coils and conduction cooled at 4.6 K. The nominal current is 20.5 kA at 4.1 T peak field in the windings and the stored energy is 250 MJ per toroid. Prior to final testing of the entire ATLAS Toroidal system, each End Cap Toroid passed a commissioning test up to 21 kA to guarantee a reliable performance in the final assembly. In this paper the test results are described. It includes the stages of test preparation, isolation vacuum pumping and leak testing, cooling down, step-by-step charging to full current, training quenches and quench recovery. By fast discharges the quench detection and protection system was checked to demonstrate a safe energy distribution within the magnet after a quench or a triggered fast dump.
IEEE Transactions on Appiled Superconductivity 07/2009; · 1.04 Impact Factor
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[show abstract]
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ABSTRACT: The ATLAS Experiment at the LHC (CERN) has a toroidal magnet system composed of one barrel toroid and two end cap toroids powered in series at 20.5 kA with a total stored energy of 1.6 GJ. So far the three magnets have been tested independently. In preparation of the overall magnet system test, here we review the quench behavior under normal and faulty conditions including the information gained from the test of the three single magnets. In particular the consequences of variations in effective quench detection and quench heater activation times are studied. The effects on energy re-distribution, peak temperatures and internal voltage in the three toroids and between the 8 coils within a single toroid are investigated. Based on simulation studies partly verified by experiments, conclusions regarding the quench performance of the entire system are drawn.
IEEE Transactions on Appiled Superconductivity 07/2009; · 1.04 Impact Factor
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[show abstract]
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ABSTRACT: ATLAS is a general-purpose detector designed to run at the highest luminosity at the CERN Large Hadron Collider. Its features include the 4 T Barrel Toroid magnet, the largest superconducting magnet (25 m long, 20 m diameter) that provides the magnetic field for the ATLAS muon spectrometer. The coils integrated at CERN, were tested individually at maximum current of 22 kA in 2005. Following the mechanical assembly of the Barrel Toroid in the ATLAS underground cavern, the test of the full Barrel Toroid was performed in October 2006. Further tests are foreseen at the end 2007 when the system will include the two End Cap Toroids (ECT). The paper gives an overview of the good mechanical test results achieved in comparison with model predictions and the experience gained in the mechanical behavior of the ATLAS Toroidal coils is discussed.
IEEE Transactions on Appiled Superconductivity 07/2008; · 1.04 Impact Factor
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D.E. Baynham,
F.S. Carr,
E. Holtom,
J. Buskop,
A. Dudarev,
G. Vandoni,
R. Ruber,
A. Foussat,
M. Losasso,
P. Benoit,
R. Pengo,
L. Stewart,
A. Olyunin,
V. Stepanov,
N. Kopeykin,
I. Shugaev,
M. Arnaud, H.H.J. ten Kate
[show abstract]
[hide abstract]
ABSTRACT: The ATLAS Experiment at LHC, CERN will utilize a large, superconducting, air-cored toroidal magnet system with a long Barrel Toroid and two End Cap Toroids. Each End Cap Toroid contains eight racetrack coils mounted as a single cold mass in a cryostat vessel of approximately 10 m diameter and 5 m length. The operating current is 20.5 kA at 0.25 GJ stored energy and a peak field of 4.1 T in the windings. This paper presents the status of the End Cap Toroid Project. Final integration of the two cold masses, 120 tons each, into their respective vacuum cryostats is described. The specialized techniques, procedures and tooling infrastructure required for these operations are explained. Pre-installation cooldown to 85 K is reported. Installation of the toroids in the ATLAS cavern 100 m underground will be described. The final interfacing to the Barrel Toroid and services in the cavern will be reviewed along with preparations for final test and commissioning.
IEEE Transactions on Appiled Superconductivity 07/2008; · 1.04 Impact Factor
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[show abstract]
[hide abstract]
ABSTRACT: Dipole magnets for the so-called SIS-300 heavy-ion synchrotron at GSI are designed to generate 6 T with a field sweep rate of 1 T/s. It is foreseen to wind the magnets with a 36 strands Nb-Ti Rutherford cable. An important issue in the cable design is sufficiently low AC loss and stability as well. In order to keep the AC loss at low level, the contact resistance between crossing strands R<sub>c</sub> is kept high by putting a stainless steel core in the cable. The contact resistance between adjacent strands R<sub>a</sub> is controlled by oxidation of the Sn-Ag coating of the strands, like in the LHC. In order to investigate the effect of Ra on the stability of the cable, we prepared four samples with different Ra by varying the heat treatment and applying a soldering technique, resulting in values between 1 muOmega to 9 mOmega. The stability of each sample against transient point-like heat pulses was measured. The results of the stability experiments and a comparison with calculations using the network model CUDI are presented. It is concluded that variation of R<sub>a</sub> has a strong influence on cable stability and that optimization of R<sub>a</sub> is mandatory to properly design the cable for the SIS-300 magnets, or likewise for similar magnets that might be used at CERN for a possible LHC injector upgrade.
IEEE Transactions on Appiled Superconductivity 07/2008; · 1.04 Impact Factor
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C. Berriaud,
F.P. Juster,
M. Arnaud,
P. Benoit,
F. Broggi,
L. Deront,
A. Dudarev,
A. Foussat,
M. Humeau,
S. Junker, [......],
C. Mayri,
G. Olesen,
R. Pengo,
S. Ravat,
J.-M. Rey,
E. Sbrissa,
V. Stepanov, H.H.J. ten Kate,
P. Vedrine,
G. Volpini
[show abstract]
[hide abstract]
ABSTRACT: The ATLAS Barrel Toroid, the largest toroid ever built with 1.1 GJ stored energy, has been successfully tested after installation in the underground cavern in fall 2006. The eight coils of the Barrel Toroid were tested individually before and showed fully acceptable performances. We observed only one training quench during an individual coil test (at 30 A below the maximum test current) and no training during the test of the fully assembled toroid. At currents up to the nominal value of 20.5 kA, the toroid has been quenched inducing normal zones by means of heaters or by stopping the helium flow in the current leads. The quench safety system worked perfectly. Given the safe peak temperatures measured in the cold mass following various quenches, it is concluded that the Barrel Toroid can be operated safely. In this paper, the hot spot of the toroid is presented in detail: the measurement data are compared to various theoretical models.
IEEE Transactions on Appiled Superconductivity 07/2008; · 1.04 Impact Factor
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[show abstract]
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ABSTRACT: Keystoned superconducting Rutherford cables are widely used in accelerator magnets like in the LHC at CERN. An essential requirement in the cable design is its stability against local heat releases in the magnet windings originating from for example, strand movement or beam loss. Beam loss is the highest at the coil inner radius of the magnet, where also the magnetic field peaks. Also the local compaction of the cable is maximum here and hence the helium content minimum. When performing stability measurements on several superconducting Nb-Ti cables used in LHC dipole and quadrupole magnets, we observed that the stability against point-like heat disturbances is much worse very close to the cable edges as compared to the central part of the cable. The main reason is related to the geometry of the cable causing variation of many parameters across the cable width, like inter-strand electrical resistance, inter-strand heat conductivity, cooled strand surfaces and RRR. In this paper we show results of new stability experiments and thoroughly compare the data with results obtained with the numerical network model CUDI, which is updated for stability simulations.
IEEE Transactions on Appiled Superconductivity 07/2008; · 1.04 Impact Factor
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ABSTRACT: We review the scaling relations for the critical current density (Jc) in Nb3Sn wires and include recent findings on the variation of the upper critical field (Hc2) with temperature (T) and A15 composition. We highlight deficiencies in the Summers/Ekin relations, which are not able to account for the correct Jc(T) dependence. Available Jc(H) results indicate that the magnetic field dependence for all wires can be described with Kramer's flux shear model, if non-linearities in Kramer plots are attributed to A15 inhomogeneities. The strain (eps) dependence is introduced through a temperature and strain dependent Hc2*(T,eps) and Ginzburg- Landau parameter kappa1(T,eps) and a strain dependent critical temperature Tc(eps). This is more consistent than the usual Ekin unification, which uses two separate and different dependencies on Hc2*(T) and Hc2*(eps). Using a correct temperature dependence and accounting for the A15 inhomogeneities leads to a remarkable simple relation for Jc(H,T,eps). Finally, a new relation for s(eps) is proposed, based on the first, second and third strain invariants. Comment: Accepted Topical Review for Superconductor, Science and Technology
08/2006;
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[show abstract]
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ABSTRACT: We performed simulations with the numerical CUDI-CICC code on a typical short ITER (International Thermonuclear Experimental Reactor) conductor test sample of dual leg configuration, as usually tested in the SULTAN test facility, and made a comparison with the new EFDA-Dipole test facility offering a larger applied DC field region. The new EFDA-Dipole test facility, designed for short sample testing of conductors for ITER, has a homogeneous high field region of 1.2 m, while in the SULTAN facility this region is three times shorter. The inevitable non-uniformity of the current distribution in the cable, introduced by the joints at both ends, has a degrading effect on voltage–current (VI) and voltage–temperature (VT) characteristics, particularly for these short samples. This can easily result in an underestimation or overestimation of the actual conductor performance. A longer applied DC high field region along a conductor suppresses the current non-uniformity by increasing the overall longitudinal cable electric field when reaching the current sharing mode. The numerical interpretation study presented here gives a quantitative analysis for a relevant practical case of a test of a short sample poloidal field coil insert (PFCI) conductor in SULTAN. The simulation includes the results of current distribution analysis from self-field measurements with Hall sensor arrays, current sharing measurements and inter-petal resistance measurements. The outcome of the simulations confirms that the current uniformity improves with a longer high field region but the 'measured' VI transition is barely affected, though the local peak voltages become somewhat suppressed. It appears that the location of the high field region and voltage taps has practically no influence on the VI curve as long as the transverse voltage components are adequately cancelled. In particular, for a thin conduit wall, the voltage taps should be connected to the conduit in the form of an (open) azimuthally soldered wire, averaging the transverse conduit surface potentials initiated in the joints.
Superconductor Science and Technology 06/2006; 19(8):783. · 2.66 Impact Factor
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ABSTRACT: We analyzed the current distribution in three Bi-2223/Ag tapes with different filament lay-out, comparing the results of magnetic knife and Hall probe experiments. Detailed knowledge of the current distribution can be useful for the diagnostics of HTS conductors. The lateral current distribution was measured with the non-destructive magnetic knife technique and used to calculate the corresponding magnetic field profile above the tape. These calculated profiles were then compared to those actually measured by a Hall probe. Additionally, the Hall probe data were also compared with "ideal" field profiles, assuming uniform current flow across the tapes. This assumption is often used in measurement interpretation. The Hall probe -and magnetic knife data correspond very well, but deviate significantly from the ideal profiles. Further analysis of the current distribution shows that this deviation is mainly due to suppression of the critical current density at the tape edges.
J. Phys.: Conf. Ser. 01/2006; 4389112.
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ABSTRACT: Differences in the thermal contraction of the composite materials in a cable in conduit conductor (CICC) for the International Thermonuclear Experimental Reactor (ITER) in combination with electromagnetic charging cause significant axial, transverse and bending strains in the Nb3Sn layer. These high strain loads degrade the superconducting properties of a CICC. Here we report on the influence of periodic bending load, using different bending wavelengths from 5 to 10 mm on a Nb3Sn powder-in-tube processed strand. The strand axial tensile stress–strain curve, the critical current versus applied axial strain results, the influence of cyclic loading on the RRR and assessment of the current transfer length from AC loss measurements, required for the analysis, are presented as well. For the strand under investigation, we find an influence of bending strain on the Ic that corresponds well to the predictions obtained from the applied classical relations, distinguishing ultimate boundaries of high and low interfilament electrical resistance. The reduction versus applied bending strain is similar for all wavelengths and equivalent to the low transverse resistance model, which is consistent with the estimated current transfer length. The cyclic behaviour in terms of critical current and n-value involves a component representing a permanent reduction as well as a factor expressing reversible (elastic) behaviour as a function of the applied load. The results from the set-up enable a discrimination in performance reduction per specific load type and per strand type. In this paper, we discuss the results of the pure bending tests.
Superconductor Science and Technology 11/2005; 18(12):S273. · 2.66 Impact Factor
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ABSTRACT: The reversible axial strain dependence of the critical current of MgB2 conductors is shown to vary with the temperature and magnetic field. The measured critical temperature and irreversibility field are also found to change reversibly with the axial strain. Combining these effects, we show empirically how the strain dependence of the whole critical surface can be scaled with just three parameters: the strain dependences of its three corner points.
Superconductor Science and Technology 11/2005; 18(12):S253. · 2.66 Impact Factor
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ABSTRACT: For a few years there has been an increasing effort to study the impact of (bending) strain on the transport properties of superconducting wires. As the stress distribution, originated by differences in the thermal expansion and electromagnetic load, is the driving factor for the final strains, the axial and transverse stiffness of the strand play a crucial role in the final performance. Since the strain state of the Nb3Sn filaments in strands determines the transport properties, basic experimental stress–strain data are required at the strand level for accurate modelling and analysis and eventually for optimizing cable and magnet design. We performed axial tensile stress–strain measurements on several types of Nb3Sn strands used for the manufacture of the International Experimental Thermonuclear Reactor (ITER) central solenoid and toroidal field model coils and a powder-in-tube processed wire. In total 48 wire samples were tested at boiling helium, boiling nitrogen and at room temperature. We present the computation of the stress–strain characteristic with a straightforward 1D model using an independent materials database, obtaining a good agreement with the experimental results. The details from the take-off origin of the measured stress–strain curves are discussed and the data are evaluated with respect to some commonly used functions for fitting stress–strain curves. The measurements are performed in the new setup TARSIS (test arrangement for strain influence on strands). A double extensometer connected to the sample enables us to determine the strain level whereas a load cell is used to monitor the stress level. For higher levels of applied stress (100 MPa), we found typically a higher strain for bronze route wires compared to a powder-in-tube and internal tin type of strand. Stress–strain results are essential to assess more accurately the impact of thermal and electromagnetic induced stress on the strain state of the Nb3Sn filaments for wires from various manufacturing processes.
Superconductor Science and Technology 10/2005; 18(11):1523. · 2.66 Impact Factor
