Flux pumps are DC superconducting power supplies capable of rapidly charging superconducting magnets to high currents[1,2]. Flux pumps using 2nd generation high-temperature superconductors (2G HTS) are rapidly progressing in development[3,4], but have yet to reach the high currents (>10 kA) of earlier low-temperature superconducting (LTS) flux pumps[5]. Increasing the current output of HTS flux pumps to >10 kA will show relevancy to high-current applications such as the toroidal field coils of next-generation fusion devices[6].
Here, we present the design methodology for HTS transformer-rectifier flux pumps. Using this methodology, devices of arbitrary current output can be rapidly developed and built. The basis of this is several studies on high-current transformer-rectifier components. These include: testing of HTS transformers using multi-wire, stacked-tape cable for secondary windings at 77 K; the asymmetry of critical current of single- or multi-wire switch elements using iron-core applied-field switches; and demonstration of a new method of operation for full-wave transformer-rectifier, capable of increasing experimental current output from 35 A to more than 275 A. Using this methodology, a preferred design for a 10 kA flux pump is presented.
[1] L. J. M. van de Klundert and H. H. J. ten Kate, “Fully superconducting rectifiers and fluxpumps Part 1: Realized methods for pumping flux,” Cryogenics, vol. 21, no. 4, pp. 195–206, Apr. 1981, doi: 10.1016/0011-2275(81)90195-8.
[2] L. J. M. van de Klundert and H. H. J. ten Kate, “On fully superconducting rectifiers and fluxpumps. A review. Part 2: Commutation modes, characteristics and switches,” Cryogenics, vol. 21, no. 5, pp. 267–277, May 1981, doi: 10.1016/0011-2275(81)90002-3.
[3] T. A. Coombs, J. Geng, L. Fu, and K. Matsuda, “An Overview of Flux Pumps for HTS Coils,” IEEE Trans. Appl. Supercond., vol. 27, no. 4, p. 4600806, Jun. 2017, doi: 10.1109/TASC.2016.2645130.
[4] J. Geng, C. W. Bumby, and R. A. Badcock, “Maximising the current output from a self-switching kA-class rectifier flux pump,” Supercond. Sci. Technol., vol. 33, no. 4, p. 045005, Apr. 2020, doi: 10.1088/1361-6668/ab6957.
[5] G. B. J. Mulder, H. H. J. ten Kate, H. J. G. Krooshoop, and L. J. M. van de Klundert, “Development of a thermally switched superconducting rectifier for 100 kA,” IEEE Trans. Magn., vol. 27, no. 2, pp. 2333–2336, Mar. 1991, doi: 10.1109/20.133685.
[6] A. J. Creely et al., “Overview of the SPARC tokamak,” J. Plasma Phys., vol. 86, no. 5, p. 865860502, Oct. 2020, doi: 10.1017/S0022377820001257.
This work was supported in part by the New Zealand Ministry of Business, Innovation and Employment (MBIE RTVU1916), and has been part-funded by STEP, a UKAEA programme to design and build a prototype fusion energy plant and a path to commercial fusion.