[WBP2] Bulk, Assembled Conductors, AC Loss

[WBP2-26] Porosity Reduction and Flux-Pinning Optimisation in SDMG-Grown GdBCO/Ag Bulk Superconductors for HTS Undulators

*Filip Antoncik^1,2, T Hlasek^2,1, M Lojka^1,2, V Sevcik¹ (1. University of Chemistry and Technology, Prague (Czech Republic), 2. CAN SUPERCONDUCTORS s.r.o. (Czech Republic))

Keywords:

REBCO,Bulks,SDMG

Critical current density is the most important application property of high-temperature superconductors, as it limits both the current-carrying capacity of REBCO-coated conductors and trapped magnetic fields in REBCO bulks. While the current carrying capacity has been extensively optimised in coated conductors, it has been rather difficult to tailor REBCO bulks to the same extent, primarily due to the difficulties connected to their melt processing. However, the recently developed Single-Direction Melt Growth (SDMG) has proven to be more robust and thus offers newfound approaches to tailor bulk microstructure. In order to maximise critical current, the microstructure should ideally be as dense as possible, without cracks, voids and large impurities, while also providing a sufficient amount of pinning centers for a given application. Thus, to fully optimise critical current in REBCO bulks, the microstructure needs to be tailored on the scale from the millimeter scale down to even sub-nanometer size. In this work, we present a synthesis of dedicated nano-sized pinning via reverse coprecipitation and its integration into GdBCO/Ag matrix via SDMG. Furthermore, we demonstrate a method for porosity elimination by preform densification before SDMG, reducing the final porosity to under 1% (based on image analysis). Finally, the growth conditions and optimisations during SDMG are presented. The results and next steps are discussed in the context of the primary projected application – HTS undulator prototype based on SDMG-grown GdBCO/Ag bulks, designed and produced by PSI.