Modeling and validation of nonlinear voltage-current characteristics of ITER PF joint sample tested in the SULTAN facility

J. Huang*, T. Bagni, Y. Ilyin, A. Nijhuis

*Corresponding author for this work

Research output: Contribution to journalArticleAcademicpeer-review

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Abstract

The International Thermonuclear Experimental Reactor poloidal field (PF) coils are wound into double pancakes with NbTi cable-in-conduit conductors, which are connected by joints in shaking hands lap-type configuration. The coils are operating in pulsed mode with a maximum operating current of 55 kA and peak magnetic field of 6.4 T, utilizing electromagnetic load on the conductors and joints. A series of PF qualification joint samples modified in praying hands configuration is measured in the SULTAN facility. For some samples, a nonlinear voltage-current (VI) characteristic is observed during the assessment of joint resistance. The growth of joint resistance versus the B I product is larger than what is expected from the magneto-resistant copper contribution. Two non-homogeneous contact resistance models are developed and combined to quantitatively evaluate the reason for the nonlinear VI behavior in combination with the relevant power dissipation and current redistribution in the joint. The simulations reveal that, for the particular pre-qualification PFJEU2 sample with resistance variation up to 3.5 nΩ, the most probable reason for the nonlinear VI characteristic is a widely spread defective connection between copper sole and shim. The electromagnetic force involves a separation effect on the mechanically and electrically weakly connected parts, resulting into a varying resistance depending on transport current and background field. The hypothesis and models are validated by an experiment on a similar sample PFJEU3 and a post-mortem examination of the PFJEU2 sample.

Original languageEnglish
Article number025014
JournalSuperconductor science and technology
Volume35
Issue number2
Early online date7 Jan 2022
DOIs
Publication statusPublished - 1 Feb 2022

Keywords

  • electromagnetic force
  • ITER
  • joint resistance
  • nonlinear voltage-current
  • numerical modeling
  • Poloidal Field
  • UT-Hybrid-D

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