Low loss striated YBa2Cu3O7−d coated conductor with filamentary current sharing

Abstract

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Acceptable coupling losses in coated conductors at industrial frequencies without twisting the superconducting stripes

“…The induced currents are then "short circuited" through the NM segments and the losses in the substrate are negligible. [24][25][26][27]41 If the buffer layer is destroyed only partially, the "internal twist" 42,43 can help at reducing the coupling losses. The idea of employing oxidized surface 27 can increase the substrate resistance, too, decreasing thus substantially the coupling losses in the substrate.…”

“…33 Most measurements were performed on striated samples with b = 10 mm with N =20 stripes of width w = 0.48 mm and distance D Ϸ 20 m between them. [24][25][26][27][34][35][36][37] The thickness of the normal coating was between 20 and 50 m. I take in the following the value h =50 m, which may consist from a sheet of NM before striating and an additional coating afterward. Taking the parameters L = 10 cm, d = b / 4 = 2.5 mm, and eff Ϸ 0.4 Cu =10 −9 ⍀ m, 28,29 this ratio is…”

“…Therefore, twisting the stripes-like in superconducting cables-seemed to be inevitable. [26][27][28][29] The requirements for the twist length of such structure are very severe, 28,29 and only hardly to be realized without decreasing j c or even destroying the superconductivity in them. In addition, twisting of CCs appears to be presently a big challenge for the superconducting community, although some progress is achieved, e.g., by the Roebel technique.…”

Magnetic-field dependence of the critical currents in a periodic coplanar array of narrow superconducting strips

“…Carr and Oberly [23] have suggested that that the ac losses in tapes several millimeters wide could be reduced by first subdividing the tapes by striations and then twisting the tapes. Analytical and experimental results pursuing this idea have been reported in [24,25,26,27,28,29,30,31,32,33,34,35,36,37]. Ashworth and Grilli [38] have recently proposed a variation of this approach, in which the tape is also subdivided into narrow parallel filaments, but instead of twisting the tape, the filaments are interrupted periodically by transverse cross-cuts bridged with normal metal.…”

“…where the real quantitiesP 1 ,P 2 ,Q 1 andQ 2 are defined viaP (ã,b, iL/π) =P 1 + iP 2 andQ(ã,b, iL/π) =Q 1 + iQ 2 , h,h, and p are defined via (28), (55), and (32), and i c (h, p, θ) = I c /I s0 . For given values of the strip width 2w, periodicity length L, dimensionless applied field h, and dimensionless bulk pinning strength p, numerical solutions of (54), (56), (57), and (58) yield the strip's dimensionless critical current i c (h, p, θ) as well as the three other unknowns,ã (or a),b (or b), andh.…”