Metallographic analysis of 11 T dipole coils for High Luminosity-Large Hadron Collider (HL-LHC)
By S. Balachandran, Jonathan Cooper, Orion B Van Oss, P. Lee, L. Bottura, A. Devred, F. Savary, C. Scheuerlein, Felix Wolf. 2020
217 citations recorded by the source corpus.
For next-generation accelerator magnets for fields beyond those achievable using Nb–Ti, Nb3Sn 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 Nb3Sn magnets will be installed in an accelerator. Nb3Sn is a brittle intermetallic, so magnet coils are typically wound from composite strands containing ductile precursors before heat treating the wire components to form Nb3Sn. 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 Nb3Sn filaments in a prototype dipole that resulted in degraded magnet performance. The cracking of the Nb3Sn, 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 Nb3Sn conductor, as evidenced by a measured Cu stabilizer hardness of 85 HV0.1, which is higher than the Cu stabilizer hardness in a reference Nb3Sn 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 Nb3Sn 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 Nb3Sn magnets to composite designs involving high work hardening materials.
Subfields: Aerospace Engineering, Biomedical Engineering, Materials Chemistry
View Paper: https://www.semanticscholar.org/paper/85b1914951072e0105477727cd05e9920a25c87c
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In Aerospace Engineering
- U. Basel
- D. University
- A. Valente-Feliciano
- Carlo Oleari
- Silvia Pascoli
- Michael Spannowsky
- Michael J. Reece
- J. Albacete
In Biomedical Engineering
- A. Stenvall
- D. Marzocca
- S. Descotes-Genon
- A. Valente-Feliciano
- M. Mangano
- Michael Spannowsky
- Ansgar Denner
- Atlas Collaboration
In Materials Chemistry
- T. O. S. University
- A. Valente-Feliciano
- Michael J. Reece
- Marco Zanetti
- Fabio Maltoni
- Jan Heisig
- M. Drewes
- Alexander Rothkopf
Citations in the corpus
- FCC-hh: The Hadron Collider (2019, background): “Superconducting links in the tunnel, already under study for the HL-LHC project [244], would greatly simplify the powering of multiple circuits.”
- Future physics opportunities for high-density QCD at the LHC with heavy-ion and proton beams (2018, background): “3 T LHC dipoles will be replaced by an assembly consisting of two shorter higher-field 11 T dipoles with the TCLD in between [38].”
- Searching for long-lived particles beyond the Standard Model at the Large Hadron Collider (2019, background): “[340, 341] for an overview); to reject particles originating from pile-up vertices; and to maintain object reconstruction in the highluminosity environment.”