The dependence of AC loss characteristics on the space in stacked YBCO conductors

Abstract

Four 5 mm wide YBCO conductors were assembled face to face to obtain a stacked YBCO conductor (YBCO stack). The space between the conductors composing the YBCO stack was set at 1.0 mm to investigate the influence of the space on AC loss characteristics. The magnetization losses without transport current, the transport losses without external magnetic field, and total AC losses of the YBCO stack carrying various transport currents in transverse magnetic fields with various orientations were measured. The measured AC losses in the YBCO stack were compared with those in a 0.2 mm space YBCO stack composed of the same conductors used in the 1.0 mm space YBCO stack as well as a single YBCO conductor. Magnetization loss without transport current in a YBCO stack decreases with decreasing space between the conductors in low and intermediate magnetic field. Transport loss without external magnetic field in a YBCO stack increases with decreasing space between conductors. There are three characterized regions, when comparing the total AC losses in the two YBCO stacks with different space between the conductors composing the stacks: (a) in the low magnetic field region, the total AC losses in the YBCO stack with smaller space are larger than those in the YBCO stack with larger space, (b) in the intermediate magnetic field region, the total AC losses in the YBCO stack with smaller space are larger than those in the YBCO stack with larger space, (c) in the high magnetic field region, the total AC losses in both YBCO stacks agree well with those in the single YBCO conductor as well as Brandt and Indembom’s analytical values.

AC losses in coated conductors

“…The auxiliary function g(x) = (2/x) ln(cosh(x)) − tanh x behaves as x 3 /6 at x 1 and its asymptote is 1 for x 1. The prediction of this model is surprisingly good, and Jiang et al [10] demonstrated that it can also be extended to angles differing from α = 90 • . However, when approaching the parallel configuration of the applied field, this modified strip model starts to deviate from the prediction.…”

Dynamic Resistance Measurement of a Four-Tape YBCO Stack in a Perpendicular Magnetic Field

“…Interestingly, we see that the measured Bth values for the stack are significantly larger than the single conductor. We attribute this to a shielding effect from circulating current present in each wire in the stack [12,13]. This effect is more significant when the dc current value is small, and becomes weaker with increasing dc current.…”

“…Dynamic resistance is a form of hysteretic ac loss, and results in a parasitic heat load on the cryogenic system. For some high current applications, it is essential to assemble multiple HTS wires into stacks [12,13]. Therefore, it is important to understand the dynamic loss characteristics of HTS stacks carrying dc current when exposed to an external ac magnetic field.…”

Numerical simulations of the angular dependence of magnetization AC losses: coated conductors, Roebel cables and double pancake coils

“…For double (or single) pancake coils (or stacks of tapes) the magnetisation AC loss of stacks of tapes was simulated only for perpendicular applied fields in [23,24,20,25,21,26].The only measurements on the angular dependence of the AC loss are in [27]. However, there exists extensive work on coated conductors [28,29] and stacks of them [30,31,32]. All these measurements for single tapes and stacks were for coated conductors at an early stage of development, with poor artificial pinning and anisotropies approximately elliptical.…”