High Temperature Superconductors (HTS) are attractive in applications that require operation in moderate, or high, magnetic field such as persistent current switches, flux pumps, and the field windings of rotating machines. In these applications the HTS coated conductors carry a DC current under an external AC magnetic field. In such operating conditions, dynamic resistance will occur when the amplitude of the AC magnetic field exceeds the threshold magnetic field due to the traversing magnetic field across the HTS conductors and shielding current will be induced in the edges of the conductors [1]. Consequently, total loss is the AC loss within the superconductors that consists of the dynamic loss component arising from dynamic resistance and the magnetization loss component caused by the shielding current [2]. Dynamic resistance sets a limit for available current for flux pumps [3, 4]. Total loss leads to a parasitic heat load to the cooling system and poses challenges for the HTS applications.

Here, we review our recent research into measurement and simulation of dynamic resistance and total loss in single REBCO coated conductors/stacks/coils at various operating temperatures between 77 K and 65 K, when the REBCO conductors carry DC currents exposed to external magnetic fields. The transport DC current level, the magnetic field amplitude and the frequency of the AC magnetic field have been varied to study the influence of these parameters on the dynamic resistance and the total loss. We show superposition of the DC current and the shielding current at high DC current level in single conductors, influence of shielding effect on total loss of the stacks, and effect of coil shape on the AC loss components of the coils [2].

[1] T. Ogasawara et al., Cryogenics 19 pp. 736-740 (1979).
[2] Y. Sun et al., Supercond. Sci. Technol. 34 065009 (2021).
[3] Z. Jiang et al., Appl. Phys. Lett. 105 112601 (2014).
[4] J. Geng et al., Appl. Phys. Lett. 107 142601 (2015).
[4] Z. Jiang et al., Supercond. Sci. Technol. 31 035002 (2018).

Keywords: HTS REBCO coated conductors, Dynamic resistance, total loss

Acknowledgment
This work was supported by the New Zealand Ministry of Business, Innovation and Employment (MBIE) under contract no. RTVU1707 and Strategic Science Investment Fund “Advanced Energy Technology Platforms” contract RTVU2004.

Keywords: Dynamic resistance, Total loss, REBCO coated conductors, HTS