Hybrid electric propulsion has been identified as a potential solution to the ambitious environmental emissions and noise targets of the aerospace industry. Superconducting machines may be the key component of that topology enabling the high power densities and efficiencies needed in aerospace. Fully superconducting machines, however, are not a mature technology. This paper looks at the different machine design configurations focusing on the stator magnetic circuit of a fully superconducting motor. The motor has been designed for an aerospace distributed fan propulsion motor with an aerospace benchmark specification of 1 MW. The AC fully superconducting machine includes superconducting bulk magnets mounted on a conventional rotor core and an MgB$_{2}$ superconducting wire wound stator. The AC losses in the stator winding are particularly sensitive to exposure to the main rotor field so different screening solutions were used to shield the superconducting windings from the rotor field. The effectiveness of the screening techniques for the stator coils and the impact on the machine performance and weight were evaluated for different stator designs, such as full stator core and air core with and without flux diverters. Various combinations of pole numbers, diverter geometries and magnetic materials have been checked. Results show that there is a trade-off between stator iron losses and superconducting losses.

High-Temperature Superconductors (HTS) considerably accelerate the development of superconducting machines for electrical engineering applications such as fully electrical aircraft. This present contribution is an overview of different superconducting materials that can be used as magnetic screens for the inductor of high specific power electrical machines. The impact of the material properties, such as the critical temperature ($T_c$) and the critical current density ($J_c$), on the machine performances is evaluated. In addition, the relevance to flux modulation machines of different HTS bulk synthesis methods are addressed.

The SuperRail project consists in the development, manufacturing, installation and long-term operation of a high temperature superconducting (HTS) dc cable system for railway applications. The objectives of the project are to reinforce the power supply of the Montparnasse railway station in Paris, to increase the traffic and to participate to the reduction of CO ₂ emission. The saturated underground in the center of Paris does not allow to create new right of ways and only the HTS cable technology allows to carry the required power to railway tracks using the few available 100 mm conduits left. The HTS cable system must answer to a load chart with a high level of requirements corresponding to the connection of a substation to a set of railways tracks in very constraints areas. In the case of SuperRail, two 60-meter long 1.5 kV–3.5 kA HTS dc cables made of second-generation (2G) conductors will be installed in parallel. They need to sustain a 67 kA–200 ms short-circuit current. The cryogenic system is specifically designed for this project. It is based on a Reverse Turbo-Brayton cycle producing cooling power of about 1700 W at 67 K. This system intends to ensure low maintenance during life cycle, high reliability and would be scalable for future application (not limited to railways). In parallel, prospective studies are being carried out to simulate superconducting cables in railway networks, and to find original solutions to replace the current leads. SuperRail is a landmark project, as it is the first time that a dc HTS cable system is installed on a commercially operated railway network. The technologies developed have the potential to be reproduced in similar cases existing in large cities.

The use of high-temperature superconducting (HTS) cables in power systems increases the transmission capacity, whereas reducing the volume of the installation. In addition, in high current applications, HTS cables considerably reduce power losses, right-of-ways and total system mass. This paper presents different multi-physics studies to be performed to accurately design the direct current (DC) HTS cables for the future railway network planned by the French company SNCF. The process used to design DC cables for high operating current (between 5 kA and 20 kA at 1750 V) made of commercial (RE)BaCuO tapes is presented. In this design process, the critical current density dependence J _c(B, θ, T) of the superconducting tapes, the thermal properties of the materials used as well as different cable cooling configurations are considered. Finally, we discuss the selection of the appropriate cooling configuration to ensure adequate cooling of the cable.

From the applications' point of view, the advantage of low density given by MgB ₂ material must be taken into consideration, and the generation of strong magnetic flux densities using MgB ₂ should be investigated. In this paper, we have studied the magnetic properties of samples processed by a fast spark plasma sintering machine that is able to produce dense and high-quality MgB ₂ samples. Experiments were carried out both on small pieces of the samples and on large-sized samples performing trapped field measurements in a field-cooling process. For temperatures between 10 and 30 K, the results show a strong dependence of the magnetic behavior of the large-sized samples to the applied magnetic field sweep rate, whereas nothing particular appeared on the small samples. As the magnetic flux density produced by MgB ₂ bulks is directly linked to the potential of the applications, we report on the field produced at the surface of one single MgB ₂ sample of 30-mm diameter and the field produced inside a stack of two MgB ₂ samples of 20-mm diameter. A generation of magnetic flux density (magnetic polarization μ ₀ M) up to 4.80 T at 10 K and 3.92 T at 20 K inside the stack of the two MgB ₂ samples was observed under a negative supporting field of -1.47 and -1.95 T, respectively. According to these values to their very low density and to their ease of manufacturing, MgB ₂ bulks are promising materials for the applications of superconductors.