Superconducting technology applications in electric machines have long been pursued due to their significant advantages of higher efficiency and power density over conventional technology. However, in spite of many successful technology demonstrations, commercial adoption has been slow, presumably because the threshold for value versus cost and technology risk has not yet been crossed. One likely path for disruptive superconducting technology in commercial products could be in applications where its advantages become key enablers for systems which are not practical with conventional technology. To help systems engineers assess the viability of such future solutions, we present a technology roadmap for superconducting machines. The timeline considered was ten years to attain a Technology Readiness Level of 6+, with systems demonstrated in a relevant environment. Future projections, by definition, are based on the judgment of specialists, and can be subjective. Attempts have been made to obtain input from a broad set of organizations for an inclusive opinion. This document was generated Superconductor Science and Technology Supercond. Sci. Technol. 30 (2017) 123002 (41pp) https://doi.org/10.1088/1361-6668/aa833e Original content from this work may be used under the terms of the Creative Commons Attribution 3.0 licence. Any further distribution of this work must maintain attribution to the author(s) and the title of the work, journal citation and DOI. 0953-2048/17/123002+41$33.00 © 2017 IOP Publishing Ltd Printed in the UK 1 through a series of teleconferences and in-person meetings, including meetings at the 2015 IEEE PES General meeting in Denver, CO, the 2015 ECCE in Montreal, Canada, and a final workshop in April 2016 at the University of Illinois, Urbana-Champaign that brought together a broad group of technical experts spanning the industry, government and academia.

https://iopscience.iop.org/article/10.1088/1361-6668/aa833e/pdf

High power density superconducting rotating machines—development status and technology roadmap

The authors wish to express their sincere thanks to Dr Nicky Athanassopoulou, Ms Andi Jones and Dr Rob Phaal of Institute for Manufacturing Education and Consultancy Service Ltd for their excellent work in organising and facilitating the Road-Mapping exercise upon which this current work is based. The authors would also like to express their appreciation of the contribution made by the other participants at the workshop: Hari Babu Nadendla (Brunel University), Pavol Diko (Slovak Academy of Sciences), Tomas Hlasek (CAN Superconductors), John Hull (The Boeing Company), Lars Kuhn (evico), Mathias Noe (KIT), Jan Plechacek (CAN Superconductors), Yunhua Shi (University of Cambridge) and Frank Werfel (ATZ). The authors acknowledge financial support for the Road-Mapping exercise on which this work is based from the University of Cambridge EPSRC Impact Acceleration Account (EP/K503757/1).

https://iopscience.iop.org/article/10.1088/1361-6668/aad7ce/pdf

Bulk superconductors: a roadmap to applications

The paper contains a review of recent advancements in rotating machines with bulk high-temperature superconductors (HTS). The high critical current density of bulk HTS enables us to design rotating machines with a compact configuration in a practical scheme. The development of an axial-gap-type trapped flux synchronous rotating machine together with the systematic research works at the Tokyo University of Marine Science and Technology since 2001 are briefly introduced. Developments in bulk HTS rotating machines in other research groups are also summarized. The key issues of bulk HTS machines, including material progress of bulk HTS, in situ magnetization, and cooling together with AC loss at low-temperature operation are discussed.

http://iopscience.iop.org/article/10.1088/0953-2048/25/10/103001/pdf

An overview of rotating machine systems with high-temperature bulk superconductors

We report electrical conductivity fluctuation analyses on YBa2Cu3O7−d
 (noted Y-123) and Y3Ba5Cu8O18±x
 (noted Y-358) polycrystalline samples added with nano-sized ferrite cobalt (CoFe2O4) particles. Phases and microstructure have been systematically investigated using X-ray diffraction (XRD) and scanning electron microscopy (SEM). XRD results reveal that the lattice parameters change for both Y-123 and Y-358 phases. SEM observations show that the grain size is reduced with increasing the content of CoFe2O4 in the yttrium-based superconductor (YBCO) matrix The temperature dependence of electrical resistivity ρ(T) has been measured and the effect of addition of magnetic CoFe2O4 in the paraconductivity region has been reported. The thermodynamic fluctuation is obtained by analyzing the excess of conductivity on the basis of the Aslamazov–Larkin theory. The coherence length, the effective layer thickness, critical magnetic fields, and critical current density are estimated. Superconducting parameters are affected by the nanoparticle addition, and results are discussed in relevance to the structural and microstructure differences between Y-123 and Y-358.

Excess Conductivity Study in Nano-CoFe 2 O 4 -Added YBa 2 Cu 3 O 7−d and Y 3 Ba 5 Cu 8 O 18±x Superconductors

In this paper, we report on the synthesis of BaZrO3 nanostructures by novel bottom-up synthesis methods. Nanocrystals with diameters ranging from 5 to 10 nm are prepared from aqueous or multiple phase precursor solutions. In order to transform the precursor solutions into nanocrystal containing suspensions, both conventional and microwave-assisted solvothermal treatments are used. An additional heat treatment was necessary to obtain crystalline particles starting from the aqueous precursor, while crystalline particles are directly obtained after solvothermal treatment of the multiple phase precursor. The crystallinity and size of the obtained nanoparticles are investigated by means of dynamic light scattering, X-ray diffraction and transmission electron microscopy. We found that the nature of the bases used in the multiple phase precursor have an effect on the particle morphology. In general, the microwave-assisted solvothermal synthesis renders the best prospects towards small particle sizes between 3 and 5 nm in diameter with a narrow size distribution. In addition, the process exhibits higher energy efficiency, resulting in lower reaction times (5 min-2 h) in comparison with the conventional solvothermal treatment (4-24 h).

Solution-based synthesis of BaZrO3 nanoparticles: conventional versus microwave synthesis

The present manuscript addresses key issues in the course of our study of materials processing of bulk high-temperature superconductors, trapped flux and its application to a prototype axial-gap-type rotating machine. The TUMSAT group has conducted a series of studies since 2003 on the growth of GdBa2Cu3O7−δ bulk material and its application in a compact low-speed high-torque rotating machine. In the stage of material growth, gaining the advantage of a large motive torque density requires large integrated flux in the motor/generators. A large grain surface might be required with sophisticated techniques for the melt-growth texture in the bulk with optimal flux pinning. In the second stage, the in situ magnetization procedure for bulk superconductors in the applied machine is a crucial part of the technology. Pulsed current excitation by using an armature copper winding has magnetized field pole bulks on the rotor. The axial-gap flux synchronous machine studied in the past decade is a condensed technology and indicates that further scientific development is required for a future compact machine to be superior to conventional ones in accordance with the cryogenic periphery and flux stabilization.

https://iopscience.iop.org/article/10.1088/0953-2048/29/4/044005/pdf

Melt-growth bulk superconductors and application to an axial-gap-type rotating machine

Superconducting transition temperature (T c) and critical current density (J c) are two key factors that are not only crucial for probing high temperature superconducting mechanism, but also for practical applications. The simple crystal structure of FeSe is very favorable for the fabrication of thin films and wires, but its application is limited by the relatively low T c and small J c. Previous studies have found that the T c of FeSe can be significantly enhanced over 40 K by using protonation method. Here, we present a systematic study of J c and vortex properties of H+-intercalated FeSe (H x -FeSe) single crystals. The value of J c for H x -FeSe single crystal is significantly enhanced, exceeding 1.3 × 106 A cm−2 at 4 K, which is more than two orders of magnitude larger than 1.1 × 104 A cm−2 of pristine FeSe. The vortex pinning mechanism of H x -FeSe is found to be surface pinning, which is different from the dominant strong point-like pinning in pristine FeSe. Moreover, the systematic study of the vortex phase transition and the underlying mechanism provides a wealth of information for the vortex phase diagram of H x -FeSe single crystal. Our results confirm that the introduction of H+ intercalations into FeSe not only enhance the T c but also significantly increases the value of J c, which is favorable for practical applications.

/pdf/significant-enhancement-of-critical-current-density-in-h-3e07kg4x.pdf

Significant enhancement of critical current density in H+-intercalated FeSe single crystal

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Melt-growth bulk superconductors and application to an axial-gap-type rotating machine

Significant enhancement of critical current density in H+-intercalated FeSe single crystal