Highlights

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2022

Superconducting motors for electric and hydrogen-powered aircrafts

Commercial aviation is a growing source of greenhouse-effect emissions (CO2, NOx, H2O at high altitude). Indeed, the International Air Trasport Association (IATA) set 2050 as goal of complete emission-free aviation in the western world. Superconducting electric propulsion motors enable zero-emission electric and hydrogen-based aircrafts. The latter are more promising, since liquid hydrogen can cool down superconducting parts down to 20 K. In our institute, we built a unique experimental set-up to measure the self-heating power of REBCO superconducting windings in motor stators down to 20 K. This quantity should be kept as low as possible in the motor, in order to keep the low required temperatures (between 20 and 40 K). Unexpectedly, measurements showed that for the measured coil, residual substrate magnetism is dominant, becoming a warning to tape producers. We also worked on concepts to reduce cross-field demagnetization effects in rotors made of REBCO superconducting stacks of tapes, which act as strong permanent magnets.

  • Kováč, J., Kopera, L., Pardo, E., Melišek, T., Ries, R., Berberich, E., Wolfstädler S., and Reis, T.: Measurement of AC loss down to 25 K in a REBCO racetrack coil for electrical aircraft motor, Sci Reports 12 (2022) 16454.
  • Dadhich, A., Li, S., Solovyov, M., Šouc, J., Mošať, M., and Pardo, E.: Reducing cross-field demagnetization of superconducting stacks by soldering in pairs, Supercond. Sci Technol. 35 (2022) 115001.

Magnetic field penetration in superconducting thin films for radiofrequency accelerating cavities

The Department of Superconductors participates in the European project I.FAST and is involved in tasks aimed at the development and optimization of new types of superconducting thin film coatings for radio frequency resonant cavities, which are used to accelerate and form elementary particle beams in accelerators. Our task is focused at complex characterization of the superconducting properties of the developed thin films and multilayers. Studying the surface defects of thin Nb films, we were able to confirm the connection between the field of the first penetration of the magnetic flux into the superconducting layer and the magnetic field enhancement near the defects. We also found that the magnetic field enhancement factor, calculated for the typical surface defects using Finite Element Method (FEM), is a much better indicator of the first penetration field value than the commonly used average surface roughness. While the surface roughness is affected by all the defects occurring at the surface of the surface superconducting film, calculating the amplification factor allows identifying the defects causing the highest local field amplification that are thus the most critical for the start of the magnetic field penetration.

a) The modeled pit defect with diameter d = 0.6 micron, height h= 1 micron and zero edge curvature radius. A dashed curve represents a pit using curvature radius c = 1 micron. b) Magnetic field distribution around a pit defect, calculated using a 2D Comsol model considering d = 0.6 micron, h = 1 micron and c = 0.1 micron.
  • Ries, R., Seiler, E., Gömöry, F., Medvids, A., Onufrijevs, P., Pira, C., Chyhyrynets, E., Malyshev, O.B., and Valizadeh, R.: Surface quality characterization of thin Nb films for superconducting radiofrequency cavities, Supercond. Sci Technol. 35 (2022) 075010.
  • Ries, R., Seiler, E., Gömöry, F., Medvids, A., Onufrijevs, P., Pira, C., Chyhyrynets, E., Malyshev, O.B., Valizadeh, R., Leith, S., and Vogel, M.: Numerical calculation of magnetic field enhancement and impact of surface defects on premature entry of magnetic field in thin Nb films for SRF cavities, IEEE Trans. Applied Supercond. 33 (2023) 3500405.