High-performance permanent magnets from. Applications potential

Transcription

1 High-performance permanent magnets from bulk RE-BCO superconductors- Applications potential Dr. M.Z. Wu, Dr. I. Stanca Magnetworld AG Jena February 2017

2 Outline Introduction Price factors for super-magnets Application candidates for superconducting permanent magnets Permanent magnets from HT superconductors Magnetizing RE-BCO disks by pulsed fields Conclusions References

3 Introduction When the superconducting pellet is magnetized to a high magnetic field, part of this field is trapped in the pellet and we get a superconducting permanent magnet (HTS bulk magnet) or, shortly, super-magnet. Trapped field given by: B t =Aμ 0 J c D (Bean approximation) High-T c superconductors can trap magnetic field by order of magnitude higher than the best hard ferromagnets nowadays known. Bulk, large-grain (RE)-BCO HTS have significant potential for the next generation of high magnetic field generators applications. The main disadvantage of these magnets is their low working temperature (of liquid nitrogen and below).

4 Introduction Reproduced and adapted from Akiyasu Yamamoto, Tokyo University of Agriculture and Technology The bulk superconductors can trap 17.6 T at 26K. (World-Record 2014!)

5 Price factors for super-magnets The main factors that directly affect the price of superconducting permanent magnets are: 1) the processes of melt-texturing, oxygenation, post-growth treatment and magnetization; 2) purchase of raw materials; 3) required performance of the final product.

6 Application candidates for superconducting permanent magnets Industrial market region of HTS bulk magnet among other magnetic field generators (Ref. [9])

7 Application candidates for superconducting permanent magnets Application candidates for superconducting permanent magnets to practical industries. {Ref.[9]}

8 Permanent magnets from HT superconductors The high-temperature superconductor YBCO is ideally used as pole in superconducting motors. For this 12 kw test engine, for example, 5 cm long YBCO- plate, which is grown or developed from three equally oriented samples. Reproduced and adapted from ref. [10]

9 Permanent magnets from HT superconductors The magnetization curve of YBCO solid material exhibits a remanent magnetization after passing through a magnetic field loop in positive range. The loop starting from zero over a maximum applied field and again back to zero field. So that a superconducting permanent magnet is produced. Of the external magnetic field is produced. If the external magnetic field H is rised from zero after cooling the superconductor, magnetic flux flows into the type II superconductor above the lower critical field strength Hc, in the form of flows tubes. Due to defects of the flow tubes, a field gradient buids up in the superconductor, which leads to shielding of the external field in the superconductor (inset below, R is the radius of the sample). Conversely, after lowering the external field, the flow tubes, remains in the superconductor at the defect. So that the superconductor also contains a remanent field without an external field (insert top). Reproduced and adapted from ref. [10]

10 Permanent magnets from HT superconductors Three-dimensional representation of the measured remanent field of a cylindrical YBCO sample at 77 K. The trappe field Bo is the maximum field at the center of the sample and falls outwards. b) Magnetic flux penetrates into the superconductor in the form of the flow tubes. They are developed or have foudation to defects (shown here in grey) and are aligned parallel to the applied magnetic field. Reproduced and adapted from ref. [10]

11 Permanent magnets from HT superconductors The properties of superconducting permanent magnets are mainly determined by the critical current density and the available size of the superconductor. The high-temperature superconductor YBCO can be produced as a massive cylindrical sample with a diameter up to 10 cm. The YBCO shown here has a diameter of 5 cm. Crystallographic orientation was characterized by a seed crystal. Reproduced and adapted from ref. [10]

12 Permanent magnets from HT superconductors The massive YBCO cylinders (here with a diameter of 25 mm) is temperaturedependent. The magnetic field was measured over the center of a single samples (red circles), or between two YBCO cylinders- One doped with silver (red dots) and another with zinc (blue dots). Reproduced and adapted from ref. [10]

13 Permanent magnets from HT superconductors A NdFeB magnet floate stably over a bulk YBCO superconductor cooled to 77K. Explanations: - the field lines emerging from the Nd-Fe-B magnet are converted into flux lines in the YBCO superconductor and are anchored at defects (shown in grey). This inhomogeneous field distribution in the superconductor generates not only a levitation force but also lateral restoring forces which stabilize the position of the Nd-Fe-B magnet over the superconductor. Reproduced and adapted from ref. [10]

14 Magnetizing RE-BCO disks by pulsed fields An essential problem which has to be solved in order to realize high- quality RE-BCO quasi permanent magnets is to effective magnetize the bulk RE-BCO superconductor at temperatures below 77K. Pulsed magnetic fields can be used for magnetizing RE- BCO disks. Pulsed magnetic field (PFM) technique have some advantages in comparison with ZFC or FC techniques: compactness, mobile relatively inexpensive.

15 Magnetizing RE-BCO disks by pulsed fields Components of HTS bulk magnet system [a case activated by pulsed magnetic field) {Ref. [9]}

16 Magnetizing RE-BCO disks by pulsed fields Many considerations related with PFM Pulse magnitude; Pulse duration; Temperature; Number of pulses; Shape of magnetising coil(s); Dynamics of magnetic flux during PFM process.

17 Conclusions Since the discovery HTS have been developed in thin-film, thick film, wire, tape and bulk forms. There are many interesting and exciting applications for this technology. Supermagnets made from bulk RE-BCO (RE-rare earth) are as small and as compact as the rare earth magnets but potentialy have magnetic flux densities orders of magnitude greater than those of the rare earths. The principle advantages of a superconducting magnet are size, weight and efficiency. The HTS bulk material has several advantages over superconducting wire in current density, magnet size and design simplicity, which recommend bulk supermagnets for possible medical applications such MRI or MDDS.

18 References 1. D. Litzkendorf, T. Habisreuther, M. Wu, T. Strasser, M. Zeisberger, W. Gawalek, M. Helbig, P. Görnert,,,Batchprocessing and bonding of melt-textured YBCO for motor applications, Materials Science and Engineering: B (1998) Volume 53, Issues 1 2, Pages D. Litzkendorf, T. Habisreuther, R. Müller, S. Kracunovska, O. Surzhenko, M. Zeisberger, J. Riches, W. Gawalek,,,Function elements of melt-textured YBCO for cryomagnetic applications, Physica C: Superconductivity, (2002) Volumes , Part 2,, Pages W Gawalek, T Habisreuther, M Zeisberger, D Litzkendorf, O Surzhenko, S Kracunovska, T A Prikhna, B Oswald, L K Kovalev and W Canders,,,Batch-processed melt-textured YBCO with improved quality for motor and bearing applications, Superconductor Science and Technology, (2004) Volume 17, Number D Litzkendorf, T Habisreuther, J Bierlich, O Surzhenko, M Zeisberger, S Kracunovska and W Gawalek, Increased efficiency of batch-processed malt-textured YBCO, Superconductor Science and Technology, (2005) Volume 18, Number 2, S 206-S Minzhi Wu, Preparation and melt textured growth mechanism of bulk high temperature superconductors for cryomagnetic applications, Jena, Uni. Diss; J.W. Park, K. Köhler, F. Hardinghaus, P. Jäger, K. Fischer, T. Habisreuther, W. Gawalek, D. Litzkendorf, P. Görnert, and M. Wu, Supraleitervormischung (Superconductor premix), Offenlegungsschrift DE A1 von , Internationale Anmeldung WO A1 8. Synthesis Report for contract no.: BRE2-CT : Melt Texture Processing of YBCO Material for Magnetic Levitation and Energy Conversion (Coordinator H.C. Freyhardt) T. Oka, Physica C (2007) G. Fuchs and G. Krabbes, Dauermagnete aus Hochtemperatur-Supraleitern, Physicalische Blätter 57 (2001) Nr. 5, WILEY-VCH Verlag