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Title: Metallographic autopsies of full-scale ITER prototype cable-in-conduit conductors after full cyclic testing in SULTAN: II. Significant reduction of strand movement and strand damage in short twist pitch CICCs

Prototype cable in conduit conductors (CICCs) destined for use in the Toroidal Field (TF) and Central Solenoid (CS) coils of the ITER experimental fusion reactor underwent severe cyclic loading in the SULTAN facility. Their autopsies revealed significant and permanent transverse strand migration due to the large Lorentz forces of the SULTAN test. The movement resulted in a 3 7% void fraction increase on the Low Pressure (LP) side of the longer twist pitch CICCs. However, short twist pitch conductors exhibited less than 1% void fraction increase in the LP side, as well as a complete absence of the Nb 3Sn filament fractures observed in the longer twist pitch conductors. We report here a detailed strand to cable analysis of short and longer “baseline” twist pitch CICCs. It was found that the use of Internal Tin strands in the longer “baseline” twist pitch CICCs can be beneficial possibly because of their superior stiffness—which better resist strand movement—while the use of Bronze Process strands showed more movement and poorer cyclic test performance. This was not the case for the short twist pitch CICC. Such conductor design seems to work well with both strand types. But it was found that despite the absencemore » of filament fractures, the short twist pitch CICC made from the Internal Tin strands studied here developed severe strand distortion during cabling which resulted in diffusion barrier breaks and Sn contamination of the Cu stabilizer during the heat treatment. Furthermore, the short twist pitch CICC made from Bronze Process strands preserved diffusion barrier integrity.« less
ORCiD logo [1] ; ORCiD logo [1] ;  [1] ;  [2] ;  [1]
  1. Florida State Univ., Tallahassee, FL (United States). Applied Superconductivity Center, National High Magnetic Field Lab.
  2. ITER Organization, St. Paul Lex Durance Cedex (France)
Publication Date:
Grant/Contract Number:
Accepted Manuscript
Journal Name:
Superconductor Science and Technology
Additional Journal Information:
Journal Volume: 28; Journal Issue: 12; Journal ID: ISSN 0953-2048
IOP Publishing
Research Org:
Florida State Univ., Tallahassee, FL (United States). Applied Superconductivity Center, National High Magnetic Field Lab.
Sponsoring Org:
USDOE Office of Science (SC), Fusion Energy Sciences (FES) (SC-24)
Country of Publication:
United States
75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND SUPERFLUIDITY; Nb3Sn; ITER; metallography; microscopy; CICC; Lorentz force; large scale conductors; image analysis
OSTI Identifier: