P. Verges

Superconductively levitated transport system - the SupraTrans project

SupraTrans is an innovative transportation concept based on the principle of superconductive magnetic levitation. The aim of the project is to create a fully working prototype, which proves its ability for passenger transport by explicit consideration of the compatibility between systems for propulsion, safety, positioning, power supply, transport logistics and the levitation system itself. The SupraTrans technology uses the flux pinning in high temperature superconductors (HTS) to stabilize the lateral and vertical position of the vehicle on the magnetic track. This self-stabilizing system is the main advantage of the superconductive levitation in comparison to all other levitation systems, which need electronic control and power to keep a constant distance between the train and the track.

Superconducting bulk magnets: Very high trapped fields and cracking

Improved trapped fields are reported for bulk melt-textured YBa2Cu3O7−δ (YBCO) material in the temperature range between 20 and 50 K. Trapped fields up to 12.2 T were obtained at 22 K on the surface of single YBCO disks (with Ag and Zn additions). In YBCO minimagnets, maximum trapped fields of 16 T (at 24 K) and of 11,2 T (at 47 K) were achieved using (Zn+Ag) and Zn additions, respectively. In all cases, the YBCO disks were encapsulated in steel tubes in order to reinforce the material against the large tensile stress acting during the magnetizing process and to avoid cracking. We observed cracking not only during the magnetizing process, but also as a consequence of flux jumps due to thermomagnetic instabilities in the temperature range betweeen 20 and 30 K.

Trapped magnetic fields larger than 14 T in bulk YBa2Cu3O7−x

High trapped fields were found in zinc-doped, bulk melt-textured YBa2Cu3O7−x (YBCO) material showing a pronounced peak effect in the field dependence of the critical current density. Trapped fields up to 1.1 T were found at 77 K at the surface of a YBCO disk (diameter 26 mm, height 12 mm). Very high trapped fields up to 14.35 T were achieved at 22.5 K for a YBCO disk pair (diameter 26 mm, height 24 mm) by the addition of silver and using a bandage made of stainless steel. The pinning forces and trapped fields obtained in bulk YBCO material are compared with results reported for melt-processed NdBa2Cu3O7−x and SmBa2Cu3O7−x.

Influence of the lateral movement on the levitation and guidance force in the high-temperature superconductor maglev system

After the levitation force relaxation was studied for different field-cooling height and working-levitation height, the high-temperature superconductor (HTS) bulk was horizontally moved in the lateral direction above the permanent magnet guideway. Both levitation and guidance force were collected by the measurement system at the same time. It was found that the decay of levitation force is dependent on both the maximum lateral displacement and the movement cycle times, while the guidance force hysteresis curve does not change after the first cycle. This work provided scientific analysis for the HTS maglev system design.

Melt-textured YBa2Cu3O7 based material doped with Li and Zn: Comparison of high trapped fields and pinning

The pinning forces and trapped fields obtained in bulk YBa2Cu3O7 (YBCO)-based material doped with Li are compared with results reported for melt-processed samples doped with Zn. The increase of the volume pinning force of Li doped material is twice that of Zn doped YBCO at 77 K. This leads to 20% higher magnetic fields trapped in the Li-doped sample at 77 K.

Trapped fields beyond 14 tesla in bulk YBa/sub 2/Cu/sub 3/O/sub 7-/spl delta//

Bulk YBa/sub 2/Cu/sub 3/O/sub 7-/spl delta// material with single-domain grains up to 35 mm in diameter was prepared by a modified melt-texturing process. The pinning properties were improved by chemical doping of Zn on Cu plane sites resulting in a well pronounced peak effect in the field dependence of the critical current density. Trapped fields of more than 1.1 T at 77 K have been obtained in a zinc-doped YBCO disk of only 27 mm in diameter. Higher trapped fields are observed at lower temperatures due to the increasing critical current density, however, at temperatures between 50 and 20 K, the trapped field is limited by the mechanical properties. Using a bandage made of steel, very high trapped fields were achieved in the 1 mm gap between two YBCO disks. Trapped fields up to 14.4 T were found at 22.5 K in such minimagnets containing silver precipitates, whereas the trapped fields of zinc-doped minimagnets reached values of 11.2 T at 47 K.

Very high trapped fields in neutron irradiated and reinforced YBa2Cu3O7−δ melt-textured superconductors

We report on very high trapped fields (13.3 T at 33 K) achieved in bulk YBa2Cu3O7−δ melt-textured monoliths, which were reinforced by steel tubes to compensate the tensile stress generated during activation. The flux pinning properties were improved by neutron irradiation. The resulting increase of the critical current density shifts the maximum attainable trapped fields to higher temperatures (by about 10 K).

Guideway and turnout switch for the SupraTrans project

This paper will deliver insight into technology and physics of the levitation system for the SupraTrans project, a prototype of a superconducting transportation system. The technology used herein bases on the flux pinning in melt-textured bulk YBa2Cu3O7-X (YBCO) that stabilizes the lateral and the vertical position of the vehicle above the magnetic track. A track made from permanent magnets and soft magnetic steel-yokes acting as flux collectors has been designed and its capability is presented. The concept also includes a fast electromagnetic turnout switch to establish a highly branched transportation network.

Trapped fields larger than 11 T in bulk YBa/sub 2/Cu/sub 3/O/sub 7-x/ material

Bulk YBa/sub 2/Cu/sub 3/O/sub 7-x/ (YBCO) material with single-domain grains up to 35 mm in diameter was prepared by a modified melt-texture process. Trapped fields of 1.1 T at 77 K and of 9 T at 43 K were obtained In zinc-doped YBCO material showing a pronounced peak effect in the field dependence of the critical current density. Very high trapped fields up to 11.4 T have been achieved at 17 K in YBCO material with improved mechanical properties. The tensile strength of this material was enhanced by the addition of silver. Additionally, a stainless steel tube was used in order to strengthen the sample against the magnetic tensile stresses. For application of YBCO samples in superconducting magnetic bearings, it is difficult to magnetize the superconductor to the maximum storable field. The authors present results on magnetizing the YBCO samples by applying pulsed magnetic fields.

Critical current in silver sheathed Bi-2223 tapes

Silver sheathed Bi-2223 tapes have been investigated by transport and magnetization measurements in the temperature range between 4.2 K and 77 K for magnetic fields up to 12 T. The superconducting current through the tape can be explained by assuming a network of platelike grains coupled by weak links. At high temperatures the critical current is governed by flux creep of pancake vortices within the grains. At temperatures below 40 K this intragrain critical current exceeds the intergrain Josephson current leading to a weak link limitation in the tape. In this picture the differences between critical transport and magnetization currents can be explained by a reduction of the geometrical length scale of current loops. An improvement of the weak link current density is observed in multifilamentary wires and tapes with AgCu sheath material.