High Temperature Superconductors: Numerical and Experimental Investigation of Their Electromechanical Properties for High Field Superconducting Magnets.
Pierro, Federica.
2019
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Rare-Earth-Barium-Copper-Oxide
(REBCO) superconductors are attractive materials for the development of the next
generation of high field magnets for particle accelerators and fusion machines. Compared
to low temperature superconductors, REBCO can generate higher magnetic fields.
Additionally, they can operate at higher cryogenic temperatures while maintaining high
current density, opening the ... read morepossibility to magnets that operates at temperatures as
high as 20 K. While several REBCO cabling techniques are being developed, it is
important to understand the electro-mechanical properties of both individual tapes and
full-scale cables under mechanical, thermal, and electromagnetic loads. In this work,
the relationship between mechanical loadings and electrical performance of REBCO tapes
and cables is investigated using experimental techniques and finite element analysis.
The novelty of the work lies into a set of experimental results in operational ranges
never tested before and the utilization of those results to predict the electrical
behavior of cables using finite element analysis. The findings discussed in this thesis
provide critical information for the development of improved HTS cables for high field
magnet applications. Single tapes experiments were conducted applying axial tension to
the conductor at different temperatures (4.2, 20, 40 and 77 K) and magnetic field (15,
12 T and self-field). Test results indicate that the strain dependence of the Ic
increase with increasing temperature, while it appears unaffected by changes in the
magnetic field. Tests of different manufacturers at 77 K and self-field showed that the
Ic vs. strain behavior of the tapes depends on many parameters, including the proportion
and mechanical/thermal properties of the constituent materials, the deposition process
of the buffer and REBCO layer and the orientation of the crystals compared to the
direction of the load. Single tapes measurements were then coupled with finite element
modeling to understand the behavior of two superconducting cabling options: a twisted
stacked-tape cable under electromagnetic Lorentz load and an HTS cable-in-conduit
conductor under bending and transverse compression. Two support methods were
investigated for the TSTC, demonstrating that a solid copper core provides higher
mechanical stability to the cable compared to a solder filled tube, which ultimately
results in higher critical current performance at high loads. Parametric studies on the
core geometries and material properties also showed that for softer copper (fully
annealed), a larger core diameter or an outer stainless-steel jacket is necessary to
limit the stress accumulations. For the HTS cable-in-conduit conductor, the FEA results
showed that the compaction process of the jacket could generate a significant strain on
the outer tapes of the stack. Under transverse compression, the model predicted higher
critical current degradations than in the real experiments. The finite element models
discussed in this work are not meant to replace real cable experiments, but rather
provide insights into the design of HTS cables. This approach will contribute to
accelerating the design process and reducing the cost required for
testing.
Thesis (Ph.D.)--Tufts University, 2019.
Submitted to the Dept. of Mechanical Engineering.
Advisor: Luisa Chiesa.
Committee: Makoto Takayasu, Xiaorong Wang, Michael Zimmerman, and Thomas Vandervelde.
Keyword: Mechanical engineering.read less - ID:
- pg15bt41c
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