S. Gruss

Bio: S. Gruss is an academic researcher. The author has contributed to research in topics: Superconductivity & Flux pinning. The author has an hindex of 4, co-authored 4 publications receiving 96 citations.

YBCO/Ag bulk material by melt crystalization for cryomagnetic applications

Abstract: Based on thermoanalytic investigations a melt crystallization process was developed with reduced process temperatures and process times to produce YBCO/Ag monoliths (d=26 mm) achieving the homogenous distribution of small sized Ag inclusions. The mechanical properties are improved, but the superconducting properties at 77 K, B/sub 0/ (480 mT) and F/sub N/ (40 N) are slightly reduced compared with YBCO monoliths without an addition of Ag (750 mT and 65 N). The maximum trapped flux was increased to the value B/sub 0/ 9.4 T at 26.5 K, instead of 8.4 T in the Ag-free bulk monolith.

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

Abstract: 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.

High trapped fields in melt-textured YBa/sub 2/Cu/sub 3/O/sub 7-/spl delta//

Abstract: Bulk melt textured YBCO material with single-domain grains up to 35 mm in diameter was prepared by a modified melt-texture process. The maximum trapped field B/sub o/ measured in the 1 mm gap between two single-grain disks was found to increase from 1.2 T at 75 K up to 9.6 T at 46 K, which is the highest trapped field achieved in nonirradiated samples. A strong exponential decrease of the trapped field with increasing temperature found in most of the cases can be explained by flux creep within the framework of collective pinning assuming weak pinning. A weaker B/sub o/(T) dependence and higher B/sub o/ values at temperatures between 55 and 75 K were observed in newly processed YBCO material. A pronounced peak effect found in the field dependence of the critical current density suggests strong pinning in this material. For applications of YBCO samples in superconducting magnetic bearings, an effective method for magnetizing the superconductor is required. Results of magnetizing YBCO samples by applying pulsed magnetic fields are presented.

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

Abstract: 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.

Applications of bulk high-temperature Superconductors

Abstract: Bulk high-temperature superconductors (HTSs) enable the opportunity to develop several unique applications in electrical power that are not feasible with superconducting or normal wires. The large current carrying capacity and low thermal conductivity of the HTSs allows relatively short lengths to carry large currents to low-temperature devices without introducing heat to the device. Such current leads can dramatically reduce the refrigeration requirements for devices such as SMES. The HTSs make a relatively sharp transition to a highly resistive state when the critical current density is exceeded, and this effect has suggested their use for resistive fault current limiters. The bulk HTSs may also take the form of large single-grained superconductors within which circulating currents may flow at large current density without loss. They are capable of developing magnetizations, similar to that of permanent magnets, but with much larger magnetic fields. In this case, they may be used as field-trapping components. Applications in this case include brushless synchronous motors, laboratory magnets, magnetic separation, and magnetron sputtering. The bulk HTSs may also be used as diamagnetic objects in magnetic circuits to provide new types of power devices. One application that uses this effect is an inductive fault current limiters, in which the HTS shields an iron core in an inductive circuit until some current level is exceeded. This transition increases the component from low impedance to high impedance. The diamagnetic property may also be used to create low-loss magnetic bearings for use in efficient energy-storage flywheel devices or sensitive instrumentation. The combination of diamagnetic shielding and field trapping has suggested their use in motor designs analogous to hysteresis motors. Laboratory prototypes for all of these devices have been constructed and tested, and in some cases the devices have been field tested in actual power systems. Improvements in HTS properties, such as flux pinning, mechanical strength, and the ability to grow large grains, have greatly improved the economics of applications that use bulk HTS.

Superconducting bulk magnets: Very high trapped fields and cracking

Abstract: 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

Abstract: 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 11 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 1435 T were achieved at 225 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

Zn doping of YBa2Cu3O7 in melt textured materials: peak effect and high trapped fields

Abstract: The previously introduced modified melt crystallization process (MMCP) has been applied to prepare single grain YBCO bulk material with Zn partially substituting for Cu. Hole doping was controlled by an appropriate oxidizing treatment of the as-grown bulk. A field induced pinning was indicated by a well pronounced peak of the critical current density jc in the jc vs. H relationship for the maximal oxidized (overdoped) material containing Zn, whereas pure overdoped YBCO shows no peak effect. The peak effect for Zn-doped YBCO appearing for T=77 K at a relatively high field of about 3 T can be attributed to pair breaking by locally induced magnetic moments due to in plane Zn for Cu substitution. Besides high quality of the bulk YBCO, the peak effect is the reason for the trapped field as large as 1.12 T at 77 K in the cylinder of only 25 mm in diameter.

Flux-pinning-induced stress and magnetostriction in bulk superconductors

Abstract: The development of bulk high-temperature superconductors (HTSs) and their applications has today come to a point where the mechanical response to high magnetic fields may be more important than their critical-current density and large-grain property. Reviewed in this article are the recent studies of the magneto-elastic effects which are caused by flux pinning in the superconductors. This includes the work on the giant irreversible magnetostriction and internal stress, which often cause fatal cracking of the HTS bulks as they become magnetized. The cracking is a problem that today accompanies the quest for the highest trapped field values, and the latest development in this area is also presented. While the first part is an overview of experimental efforts, the second summarizes the work done to model the pinning-induced stress and strain under various magnetic and geometrical conditions.