Shaping the critical current of high temperature superconducting coated conductors using particle irradiations

Orateur : Maxime LEROUX (Argonne National Laboratory, USA)

Remendous improvements have been made during the past decade in the performance of high temperature superconducting cables based on YBa2Cu3O7−δ (YBCO), for use in electric grid and magnet technologies. Production-line wires of hundreds of meters in length with critical current densities (Jc) exceeding 3 MA/cm2 (at 77K and self-field) are now being routinely manufactured. The cost of fabrication is now such that superconducting wires are competitive for space-limited and weight-limited applications in rotating machinery and electric power transmission : several projects involving urban grid, transformers, compact engines or offshore windmill turbines are already existing or being deployed worldwide. But widespread penetration is still limited by the high cost of fabrication. Indeed, such high Jc are achieved by strict control of the micro and nanostructure during epitaxial growth. Potential pinning centers encompass : impurities, dislocations, stacking faults, nanoparticles, nanorods… to cite just a few. As such there is plenty of room for optimization. The current manufacturing process involves a complex combination of highly engineered buffer layers, controlled addition of nanoparticles, or, more recently, inclusion of BaZrO3 (BZO) nanoparticles that self-assemble into nanorods and provide a very effective pinning. In this seminar, I will report on the synergies between the preexisting pinning structure of YBCO based cables, and different topologies of defects (point, cluster, cylinder) that we induced by irradiation with heavy-ions, protons or both. I will also present some very promising results on low energy irradiation, with exposure time of just a few tens of seconds, which would be commercially viable for a reel-to-reel manufacturing process. For instance, proton irradiation produces a mixed pinning landscape composed of pre-existing rare earth particles and a uniform distribution of irradiation induced nm-sized defects. This pinning landscape strongly reduces the suppression of Jc in magnetic fields, resulting in a doubling of Jc in a field of ∼ 4T. The irradiation dose-dependence of Jc is characterized by a temperature and field dependent sweet spot that at 5 K and 6 T occurs around 20x1016 p/cm2. Large-scale time dependent Ginzburg-Landau simulations yield a good description of our results. This work was supported by the Center for Emergent Superconductivity, an Energy Frontier Research Center funded by the U.S. D.O.E., Office of Science, Office of Basic Energy Sciences and by the D.O.E, Office of Basic Energy Sciences, under Contract No. DE-AC02-06CH11357.

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