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The Large Scale Coil (LSC) is a high-temperature superconducting (HTS) coil that has been developed and tested in the research and development efforts for the 40-T All-Superconducting Magnet Project at the National High Magnetic Field Laboratory. The LSC is composed of stacked pancake disks consisting of 2-in-hand wound rare-earth barium copper oxide coated conductor (CC REBCO) tapes with stainless steel and copper co-wind. Under high magnetic fields, Lorentz forces on the REBCO tapes can impact the performance of the coil. Therefore, it is important to accurately predict strain in the pancake disks when designing these HTS magnets. Modeling of the LSC was done in COMSOL using a T-A formation coupled with structural mechanics, while accounting for screening current induced strain.
Experimental data was collected and compared to simulated results. On the LSC, strain gauges were placed on the inboard and outboard edges of three disks, along with compensation gauges to account for magnetic field effects. The LSC was operated in a background field of 11.5 T. LSC simulations were conducted using FLOSSS (Florida Screening Strain Software) [1] [2] [3]. Initial results reveal significantly higher simulated strain at both inboard and outboard gages. Therefore, further simulations were needed to investigate the discrepancy between simulated and measured strain.
Manufactured REBCO have variations along tape width including ‘roughness’ on the tape surfaces, whereas a flat tape surface was assumed for initial simulations. Methods to address this include a penalty method [4] and introducing a gap dependent on variation in thickness along the REBCO tape. Comparison of experimental results to simulations reveal that incorporating this aspect of REBCO tape surface structure decreases the difference between simulated and experimental results.
Strain data from the LSC tests are a valuable resource for verification of modeling methods and improving our understanding and design of large and complex HTS magnets such as the 40-T. This investigation compares measured strain data with simulated strain to assess and improve our current modeling techniques for HTS coil design. Details on comparisons of strain data from experiments and simulations during cooldown, background magnet ramping, and insert current ramping will be included. In addition, implementation of simulation methods will be detailed.
[1] D. J. Kolb-Bond et al., “Computing strains due to screening currents in REBCO magnets,” IEEE Trans. Appl. Supercond., vol. 30, no. 4, Jun. 2020)
[2] D. Kolb-Bond et al., “Screening current rotation effects: SCIF and strain in REBCO magnets,” Supercond. Sci. Technol., vol. 34, no. 9, 2021
[3] Y. Suetomi et al., "Screening Current Induced Stress/Strain Analysis of High Field REBCO Coils With Co-Winding or Over-Banding Reinforcement," IEEE TAS, 34, 5, 8400206 (2024).
[4] J. Park, “A Numerical Study on Mechanical Boundary Conditions for Screening Current Induced Stress Analysis of REBCO Magnets”, ASC 2024, 5Lor1C (2024)
This work was performed at the National High Magnetic Field Laboratory, which is supported by National Science Foundation Cooperative Agreement No. DMR-2131790, DMR-2128556, and the State of Florida.
