The European Union-funded Advanced Superconducting Motor Experimental Demonstrator (ASuMED) project started in May 2017 with the purpose of demonstrating the benefits of a new, fully superconducting motor for reaching the targets established by the Flightpath 2050 plan. The project aims at a motor power density of 20kW kg−1 using a high-temperature superconducting (HTS) stator. The rotor will use HTS stacks operating like permanent magnets. A highly efficient cryostat for the motor combined with an integrated cryogenic cooling system and associated power converter will be used. This article provides a general overview of the prototype that is currently being assembled and that will be tested soon.

Stacks of superconducting tapes can trap much higher magnetic fields than conventional magnets. This makes them very promising for motors and generators.However, ripple magnetic fields in these machines present a cross-field component that demagnetizes the stacks. At present, there is no quantitative agreement between measurements and modeling of cross-field demagnetization, mainly due to the need of a 3D model that takes the end effects and real micron-thick superconducting layer into account. This article presents 3D modeling and measurements of cross-field demagnetization in stacks of up to 5 tapes and initial magnetization modeling of stacks of up to 15 tapes. 3D modeling of the cross-field demagnetization explicitly shows that the critical current density, J c , in the direction perpendicular to the tape surface does not play a role in cross-field demagnetization. When taking the measured anisotropic magnetic field dependence of J c into account, 3D calculations agree with measurements with less than 4 % deviation, while the error of 2D modeling is much higher. Then, our 3D numerical methods can realistically predict cross-field demaga This article has been published in Supercond. Sci. Technol. with netization. Due to the force-free configuration of part of the current density, J, in the stack, better agreement with experiments will probably require measuring the J c anisotropy for the whole solid angle range, including J parallel to the magnetic field.the probe is at least 10 mV/T. Cross-field demagnetization consists on the following three main steps: magnetization by field cooling (FC) method, relaxation time and cross-field demagnetization. The detailed process is the following:• The sample is placed into the electromagnet at room temperature.• The electromagnet is ramped up to 1 T.• The sample is cooled down in liquid nitrogen bath at 77 K.• The electromagnet is ramped down with ramp rate 10 mT/s. 400 405 410 415 420 425 B t /B 0 [-] t [s] cal 50 mT cal 100 mT cal 150 mT cal 50 mT n(B,θ) cal 100 mT n(B,θ) cal 150 mT n(B,θ) (b) FIG. 19: (a) The n(B, θ) measured data on a 4 mm wide SuperOx tape, measured in Bratislava by the set-up in [46]. (b) The comparison of calculation with constant n=30 and n(B, θ) dependence, both cases use J c (B, θ) dependence. Using n(B, θ) slightly reduces the demagnetization rate for a few number of cycles, but later on it is increased slightly.

Stacks of REBCO tapes can trap large amounts of magnetic fields and can stay magnetized for long periods of times. This makes them an interesting option for major engineering applications such as motors, generators and magnetic bearings. When subjected to transverse alternating fields, superconducting tapes face a reduction in the trapped field, and thus it is the goal of this paper to understand the influence of all parameters in cross field demagnetization of stacks of tapes. Major parameter dependencies considered for the scope of this paper are ripple field amplitude, frequency, tape width, tape thickness (from 1 to 20 µm), and number of tapes (up to 20). This article also provides a systemic study of the relaxation time constant τ , which can be used to estimate the cross-field demagnetization decay for high number of cycles. Modeling is based on the Minimum Electro-Magnetic Entropy Production method, and it is shown that the 2D model gives very accurate results for long samples when compared with 3D model. Analytical formulas for large number of cycles have been devised. The results show that when the ripple field amplitude is above the penetration field of one tape, the stack always fully demagnetizes, roughly in exponential decay. Increasing the number of tapes only increases the relaxation time. The formulas derived also hold when validated against numerical results, and can be used for quick approximation of decay constant. They also show that the cause of the decreases of cross-field demagnetization with number of tapes is the increase in the self-inductance of the magnetization currents. The trends and insights obtained for cross field demagnetization for stacks are thus very beneficial for engineers and scientists working with superconducting magnet design and applications.

Superconducting stacks and bulks can act as very strong magnets (more than 17 T), but they lose their magnetization in the presence of alternating (or ripple) transverse magnetic fields, due to the dynamic magneto-resistance. This demagnetization is a major concern for applications requiring high run times, such as motors and generators, where ripple fields are of high amplitude and frequency. We have developed a numerical model based on dynamic magneto-resistance that is much faster than the conventional Power-Law-resistivity model, enabling us to simulate high number of cycles with the same accuracy. We simulate demagnetization behavior of superconducting stacks made of 10–100 tapes for up to 2 million cycles of applied ripple field. We found that for high number of cycles, the trapped field reaches non-zero stationary values for both superconducting bulks and stacks; as long as the ripple field amplitudes are below the parallel penetration field, being determined by the penetration field for a single tape in stacks. Bulks keep substantial stationary values for much higher ripple field amplitudes than the stacks, being relevant for high number of cycles. However, for low number of cycles, stacks lose much less magnetization as compared to bulks.

Superconducting stacks can be used as strong permanent magnets in several applications. One of their uses is to build light and compact superconducting motors for aviation, where these magnets can be used in the rotor, but they can demagnetize quickly in the presence of cross fields. In this article, we propose a new configuration of soldered stacks face-to-face, which can be constructed by relatively simple joining techniques. Based on numerical modeling of cross-field demagnetization of stacks of 2 and 16 tapes, we show that such a sample can withstand around twice as high ripple field amplitudes than isolated stacks. The reason is the increase in the parallel penetration field by around a factor 2. For cross field amplitudes below this value, a soldered stack can retain higher permanent magnetization than isolated stacks. This way of reducing cross-field demagnetization does not decrease the power or torque rating of a motor, compared to other strategies like the increase in the gap between rotor and stator.

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The design of superconducting applications containing windings of superconducting wires or tapes requires electro-thermal quench modelling. In this article, we present a reliable numerical method based on a variational principle and we benchmark it to a conventional finite difference method that we implemented in C++. As benchmark problem, we consider a racetrack coil made of REBCO superconducting tape under short circuit, approximated as a DC voltage that appears at the initial time. Results show that both models agree with each other and analytical limits. Since both models take screening currents into account, they are promising for the design of magnets (especially fast-ramp magnets) and power applications, such as the stator windings of superconducting motors or generators.

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