The behavior of vortex matter in high-temperature superconductors (HTS) controls the entire electromagnetic response of the material, including its current carrying capacity. Here, we review the basic concepts of vortex pinning and its application to a complex mixed pinning landscape to enhance the critical current and to reduce its anisotropy. We focus on recent scientific advances that have resulted in large enhancements of the in-field critical current in state-of-the-art second generation (2G) YBCO coated conductors and on the prospect of an isotropic, high-critical current superconductor in the iron-based superconductors. Lastly, we discuss an emerging new paradigm of critical current by design-a drive to achieve a quantitative correlation between the observed critical current density and mesoscale mixed pinning landscapes by using realistic input parameters in an innovative and powerful large-scale time dependent Ginzburg-Landau approach to simulating vortex dynamics.

We demonstrate that 3.5-MeV oxygen irradiation can markedly enhance the in-field critical current of commercial 2 nd generation superconducting tapes with an exposure time of just one second per 0.8 cm 2 . The speed demonstrated here is now at the level required for an industrial reel-to-reel post-processing. The irradiation is made on production line samples through the protective silver coating and does not require any modification of the growth process. From TEM imaging, we identify small clusters as the main source of increased vortex pinning. 2Increasing the current carrying capacity of 2 nd generation (2G) YBCO high temperature superconducting (HTS) wires in the presence of high magnetic fields is critical for the commercialization of HTS based rotating machine applications such as lightweight and compact off-shore wind turbines and motors as well as various HTS magnet applications [1][2][3][4]. For these, operation in magnetic fields of several Tesla and at temperatures around 30K is envisioned. Although conductors of hundreds of meters in length with self-field critical current densities J c of more than 3 -4 MA/cm 2 (more than 300 -400 A/cm-width) at 77 K can now reliably be manufactured, the rapid suppression of J c in even modest applied magnetic fields continues to be a major challenge for HTS conductor development.In recent years, impressive advances in the in-field performance of short-length samples have been achieved [5][6][7][8][9][10], largely due to the strict control over the micro-and nanostructures. The formation of the desired pinning centers depends sensitively on the film deposition technique and substrate architecture. For instance, self-assembled nanorods can be engineered in films grown by pulsed laser deposition (PLD) or MOCVD from material containing excess metal oxides such as BaZrO 3 [11][12][13][14], BaSnO 3 [15] or BaHfO 3 [16], whereas the deposition of films with excess Zr using metal organic deposition (MOD) on single-crystal substrates [17] and on IBAD substrates [18] does not yield nanorods but nanoparticles. In general, the enhanced vortex pinning arises from the complex combined effects of the introduced second phases (nanorods or nanoparticles), additional structural disorder such as twin boundaries, stacking faults and point defects, as well as from isotropic pinning due to strain fields [5,17]. In short-length samples, critical current densities as high as ~ 7 MA/cm 2 at 30 K and 9 T applied parallel to caxis have been reported [9]. The translation of these advances into a reliable large-scale production process is a time consuming process currently under development.An alternative to increase the critical current density by modifying the chemical synthesis is afforded by particle irradiation, which may be applicable to all superconducting materials. Depending on the mass and energy of the ions and the properties of the superconducting material, irradiation enables the creation of defects with well-controlled density and topology, such as points, clusters or tracks. The...

Mixed pinning landscapes in superconductors are emerging as an effective strategy to achieve high critical currents in high, applied magnetic fields. Here, we use heavy-ion and proton irradiation to create correlated and point defects to explore the vortex pinning behavior of each and combined constituent defects in the iron-based superconductor Ba0.6K0.4Fe2As2 and find that the pinning mechanisms are non-additive. The major effect of p-irradiation in mixed pinning landscapes is the generation of field-independent critical currents in very high fields. At 7 T ‖ c and 5 K, the critical current density exceeds 5 MA/cm2.