Nb<sub>3</sub>Sn Wire Shape and Cross-Sectional Area Inhomogeneity in Rutherford Cables

Kelly, U.; Schoerling, Daniel; Richter, Sebastian; Wolf, Felix; Scheuerlein, C.; Schladitz, Katja; Lackner, F.; Ebermann, Patrick; Meinel, Dietmar; Redenbach, Claudia

doi:10.1109/tasc.2018.2791637

Cited by 8 publications

(6 citation statements)

References 17 publications

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“…1. The average cable thickness in the 11 T dipole coil of 1.054±0.208 mm has been determined by digital image analysis of 11 T coil #107 micro-tomography slices [10]. A second sample type are so-called ten-stack samples.…”

Section: A the Samplesmentioning

confidence: 99%

Effect of Applied Compressive Stress and Impregnation Material on Internal Strain and Stress State in Nb₃Sn Rutherford Cable Stacks

Wolf

Scheuerlein

Lorentzon

et al. 2019

IEEE Trans. Appl. Supercond.

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The Nb3Sn superconductor in accelerator magnets must resist high mechanical stresses. In order to understand better the effect of the coil impregnation system on the stresses exerted on the strain-sensitive Nb3Sn superconductor, we have measured the elastic strain evolution in the conductor constituents under externally applied loads. For this purpose a dedicated load frame that enables rotation of the sample load axis with respect to the neutron scattering geometry was installed in the Stress-Spec beamline at the neutron source Heinz Maier-Leibnitz FRM II. The Nb3Sn and Cu loading strain was measured in situ by neutron diffraction under monotonic and cyclic compressive loading. Socalled ten-stack samples composed of Nb3Sn Rutherford type cable with different impregnation, and coil blocks extracted from a 11 T dipole short model coil were investigated.

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Section: A the Samplesmentioning

confidence: 99%

Effect of Applied Compressive Stress and Impregnation Material on Internal Strain and Stress State in Nb₃Sn Rutherford Cable Stacks

Wolf

Scheuerlein

Lorentzon

et al. 2019

IEEE Trans. Appl. Supercond.

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“…The micro-CT was performed using a laboratory scanner with a 225 kV micro focus x-ray tube with 6 μm focal spot size and a flat panel detector with 2 11 ×2 11 pixels [15]. The spatial resolution of the micro-CT scans is 10 μm.…”

Section: X-ray Computed Tomography Of the Nb 3 Sn Rutherford Cable Do...mentioning

confidence: 99%

Irreversible degradation of Nb₃Sn Rutherford cables due to transverse compressive stress at room temperature

Ebermann

Bernardi

Fleiter

et al. 2018

Supercond. Sci. Technol.

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In the framework of the Future Circular Collider design study for a 100 TeV circular collider, 16 T superconducting bending magnets based on Nb 3 Sn technology are being developed. A prestress on the conductor during magnet assembly at room temperature (RT) is needed to counteract the Lorentz forces during operation. The superconducting properties of the brittle Nb 3 Sn superconductor are strain sensitive and excessive pre-stress leads to an irreversible degradation of the superconductor. In order to determine the level of acceptable pre-stress during the magnet assembly process, reacted and impregnated Nb 3 Sn cables were exposed to increasing transverse compressive stress up to a maximum stress level of 200 MPa at RT. After each stress cycle, the critical current of the cable specimens were characterized at 4.3 K in the FRESCA cable test station. No significant critical current degradation was observed up to 150 MPa, followed by degradation less than 4% after a nominal stress of 175 MPa. A dramatic permanent critical current degradation occurred after applying a nominal stress of 200 MPa. A comprehensive post analysis consisting of non-destructive micro-tomography followed by microscopic characterization of metallographic cable cross sections was carried out after the critical current test to reveal cracks in the Nb 3 Sn sub-elements of the loaded specimen.

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“…The ten-stack samples are made of ten 11 T dipole cables (nominal width and mid-thickness are 14.7 mm and 1.25 mm, respectively [14]), which are stacked alternatingly in order to compensate for the keystone angle of 0.79 • . The Rutherford cables are made of 40 Restacked-Rod Process type Nb 3 Sn strands with 0.7 mm nominal diameter, which were produced by Oxford Instruments Superconducting Technology (now Bruker-OST).…”

Section: Description Of 11 T Dipole Cable Ten-stack Samplesmentioning

confidence: 99%

Metallographic analysis of 11 T dipole coils for High Luminosity-Large Hadron Collider (HL-LHC)

Balachandran¹,

Cooper

Oss

et al. 2021

Supercond. Sci. Technol.

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For next-generation accelerator magnets for fields beyond those achievable using Nb-Ti, Nb 3 Sn is the most viable superconductor. The high luminosity upgrade for the Large Hadron Collider (HL-LHC) marks an important milestone as it will be the first project where Nb 3 Sn magnets will be installed in an accelerator. Nb 3 Sn is a brittle intermetallic, so magnet coils are typically wound from composite strands containing ductile precursors before heat treating the wire components to form Nb 3 Sn. However, some mechanical assembly is still required after the coils have been heat-treated. In this paper, we present direct evidence of cracking of the brittle Nb 3 Sn filaments in a prototype dipole that resulted in degraded magnet performance. The cracking of the Nb 3 Sn, in this case, can be attributed to an issue with the collaring process that is required in the assembly of dipole accelerator magnets. Metallographic procedures were developed to visualize cracks present in the cables, along with quantitative image analysis for location-based crack analysis. We show that the stresses experienced in the damaged coil are above the critical damage stress of Nb 3 Sn conductor, as evidenced by a measured Cu stabilizer hardness of 85 HV 0.1 , which is higher than the Cu stabilizer hardness in a reference Nb 3 Sn cable ten-stack that was subjected to a 210 MPa transverse compression. We also show that once the collaring procedure issue was rectified in a subsequent dipole, the Nb 3 Sn filaments were found to be undamaged, and the Cu stabilizer hardness values were reduced to the expected levels. This paper provides a post-mortem verification pathway to analyze the damage, provides strand level mechanical properties, which could be beneficial for improving model prediction capabilities. This method could be applied beyond Nb 3 Sn magnets to composite designs involving high work hardening materials.

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Nb₃Sn Wire Shape and Cross-Sectional Area Inhomogeneity in Rutherford Cables

Cited by 8 publications

References 17 publications

Effect of Applied Compressive Stress and Impregnation Material on Internal Strain and Stress State in Nb₃Sn Rutherford Cable Stacks

Effect of Applied Compressive Stress and Impregnation Material on Internal Strain and Stress State in Nb₃Sn Rutherford Cable Stacks

Irreversible degradation of Nb₃Sn Rutherford cables due to transverse compressive stress at room temperature

Metallographic analysis of 11 T dipole coils for High Luminosity-Large Hadron Collider (HL-LHC)

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Nb3Sn Wire Shape and Cross-Sectional Area Inhomogeneity in Rutherford Cables

Cited by 8 publications

References 17 publications

Effect of Applied Compressive Stress and Impregnation Material on Internal Strain and Stress State in Nb3Sn Rutherford Cable Stacks

Effect of Applied Compressive Stress and Impregnation Material on Internal Strain and Stress State in Nb3Sn Rutherford Cable Stacks

Irreversible degradation of Nb3Sn Rutherford cables due to transverse compressive stress at room temperature

Metallographic analysis of 11 T dipole coils for High Luminosity-Large Hadron Collider (HL-LHC)

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Resources

About

Nb₃Sn Wire Shape and Cross-Sectional Area Inhomogeneity in Rutherford Cables

Effect of Applied Compressive Stress and Impregnation Material on Internal Strain and Stress State in Nb₃Sn Rutherford Cable Stacks

Effect of Applied Compressive Stress and Impregnation Material on Internal Strain and Stress State in Nb₃Sn Rutherford Cable Stacks

Irreversible degradation of Nb₃Sn Rutherford cables due to transverse compressive stress at room temperature