U/N Method: Record Critical Currents Achieved by Tailored Pinning Centers.

摘要

The aim of this project was to develop significantly improved high temperature superconductor (HTS) via improved pinning. In particular the work focused on the 'U/n process' in which U is added to HTS, and then irradiated with thermal neutrons to fission some of the U-235. This process raised J(sub c) in YBa2Cu3O7 (Y123) to world record levels. The U/n process was studied in Bi1Sr2Ca2Cu3O10 (BiSCCO 2223). Again, world record J(sub c) was achieved plus record H(sub irr) and isotropy. J(sub c) and isotropy were increased by factors of up to 100, and H(sub irr) was more than doubled. U/n processing was also developed for Nd123. This is not yet optimized, but to date J(sub c) > 150,000 A/sq cm in Nd123, a world record. The increases in J(sub c) achieved are sizable, not marginal (e.g., a factor of 40 in Y123 at T = 77K, B = 0.25T). It was proven, first theoretically and then experimentally, that in the specific HTS Sm123 and Gd123 the U/n process cannot be used for large objects. The success of U/n pinning has been studied and is found to be attributable to multiple in-line defects - a domain of high-energy ion damage only sparsely studied for HTS characterizations.