Bi2Sr2CaCu2Ox (Bi-2212) conductor is the only high-temperature superconductor manufactured as a round wire and is a very promising conductor for very high field applications. One of the key design parameters of Bi-2212 wire is its filament size, which has been previously reported to affect the critical current density (Jc) and ac losses. Work with 1 bar heat treatment showed that the optimal filament diameter was about 15 μm, but it was not well understood at that time, that gas bubbles were the main current limiting mechanism. Here, we investigated a recent Bi-2212 wire with a 121 × 18 filament architecture with varying wire diameter (1.0-1.5 mm) using 50 bar overpressure processing. This wire is part of a 1.2 km piece length of 1.0 mm diameter made by Oxford Superconducting Technology. We found that Jc is independent of the filament size in the range from 9 to 14 μm, although the n value increased with increasing filament size. A new record Jc (4.2 K, 15 T) of 4200 A/mm2 and JE (4.2 K, 15 T) of 830 A/mm2 were achieved.

中文翻译：

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灯丝尺寸对超压加工 Bi-2212 圆线临界电流密度的影响

Bi2Sr2CaCu2Ox (Bi-2212) 导体是唯一一种以圆线形式制造的高温超导体，是非常有前途的高场应用导体。Bi-2212 线的关键设计参数之一是其灯丝尺寸，此前曾有报道称其会影响临界电流密度 (Jc) 和交流损耗。使用 1 bar 热处理的工作表明，最佳灯丝直径约为 15 μm，但当时还不是很清楚，气泡是主要的限流机制。在这里，我们研究了最近使用 50 bar 过压处理的具有 121 × 18 细丝结构的 Bi-2212 线材，该线材具有不同的线径（1.0-1.5 毫米）。该线材是牛津超导技术公司制造的直径为 1.0 毫米、长 1.2 公里的线材的一部分。我们发现 Jc 在 9 到 14 μm 的范围内与细丝尺寸无关，尽管 n 值随着细丝尺寸的增加而增加。实现了 4200 A/mm2 的新记录 Jc（4.2 K，15 T）和 830 A/mm2 的 JE（4.2 K，15 T）。