ORAL SESSION 2D2: Wires, Magnets & Components
Tuesday, Feb. 22, 10:15 a.m. – 12:30 p.m., 301F (GRB)
Chairs: U. Balachandran (Argonne Nat'l. Lab), H. Fujimoto (Railway Tech. Res. Inst.)
2D2.1 Phase stability and phase formation in Bi based High Tc superconductors
R. Flükiger, E. Walker, E. Giannini, M.
Lomello-Tafin, and M. Dhalle, Department of Condensed Matter Physics, University of Geneva, quai
E. Ansermet 24, CH-1211 Geneva, Switzerland
Presenting Author: R. Flükiger The critical current density in Bi,Pb(2223) tapes has not yet reached
its expected potential: better connectivity between the grains and
improved pinning properties are required. There are still uncertainties
about important details of the high temperature phase diagram and the kinetics
of phase formation. The compound Bi,Pb(2223) is formed by a
non-equilibrium process, in contrast to Bi(2212). The different phase
formation in these two phases is illustrated by the fact that the size of
Bi,Pb(2223) crystallites is limited to <100 mm, while single crystals of
Bi(2212) can presently be grown to sizes of several mm. A serious obstacle in
growing larger Bi,Pb(2223) crystallites is the irreversible reaction path,
comprising the formation of an intermediate "transient" liquid.
We have shown by high temperature neutron diffraction measurements
that the reaction path is influenced by the thermal history, in particular by
the heating and cooling conditions. We report on the effects of Tl and/or
Ba additions on the formation temperature and on the stability of
the Bi,Pb(2223) phase: DTA and TG measurements showed a marked
decrease of the formation temperature. This decrease is compared to the
one observed by other additions to Bi,Pb(2223). The effect of a high
Argon background pressure (up to 1 kbar) on the formation conditions
is discussed.
Bi,Pb(2212) single crystals, grown in
BaZrO3 crucibles, show a strongly enhanced irreversibility
field, confirming earlier results of Kishio et al.
A comparison with Bi,Pb(2212) samples obtained by the usual reaction
from calcined precursors shows that the origin of enhanced pinning in
single crystals is a markedly higher solubility of Pb. It is not excluded that
under particular conditions, a similar link between the reaction kinetics and
the microstructure could also be found in Bi,Pb(2223).
2D2.3 AFM Multilayered Bi-2223 Conductors for 13 000 A Current Leads for CERN
Luciano Martini 1, Franco Barberis 1, Renza Berti 1, Giovanni Volpini 2, Luigi Bigoni 1, and Franco Curcio 1. 1 ENEL-SRI, 20090 Segrate (MI), Italy. 2 INFN-LASA, 20090 Segrate (MI), Italy.
Presenting Author: L. Martini
Large current carrying capacity multilayered Bi-2223 conductors are reproducibly prepared by means of the "Accordion folding method" (AFM) and suitably used to manufacture the low temperature stage of 13 000 A hybrid metal-HTS current leads (CLs) for CERN. Because of their large fill factor, f.f.@ 0.7, AFM conductors with silver-gold matrix allow for very low heat load into the liquid helium with respect to conventional all-metal CL. Nevertheless, this small amount of resistive matrix is still sufficient to enhance the mechanical strength of the conductor.
In this work, we report on the electrical characterisation of AFM multilayered Bi-2223 conductors having typical external dimensions of about 1.1 x 11 x 400 mm and critical current as high as 400 A at 77 K, self-field. A specific experimental set-up has been developed to study the thermo-electrical performances of the AFM Bi-2223/Ag-Au conductors during the sudden resistive transition of the HTS: quench event. The quench has been induced by rising the temperature at one or both ends of AFM conductors for different constant current values. During the quench measurements, the voltage drop across the whole AFM conductor as well as the temperature profile along the specimen have been sampled every second to have an insight of quench propagation. Evolution of temperature profile for AFM multilayered Bi-2223 conductors with different matrix composition, namely pure silver and silver-gold alloys with 3 and 11% wt gold, are reported and discussed.
2D2.4 Massive HTS Material in Rotating Electric Machines*
Wolfgang Gawalek 1, Tobias Habisreuther 1, Matthias Zeisberger 1, Doris Litzkendorf 1, Olekseiy Surzhenko 1, Torsten Strasser 2, Juergen Best 2, Bernhard Oswald 2, Wolfgang R.Canders 3, Hardo May 3, Hubert Weh 3, Kostya V. Ilushin 4, Vladimir T.Penkin 4, and Lev K. Kovalev 4. 1 Institut fuer Physikalische Hochtechnologie e.V., Winzerlaer Strasse 10, 07745 Jena, Germany. 2 OSWALD Elektromotoren GmbH, Benzstr. 12, 63897 Miltenberg, Germany. 3 Institut für Elektrische Maschinen, Antriebe und Bahnen, TU Braunschweig, Hans-Sommer-Straße 66, 38106 Braunschweig, Germany. 4 Moscow State Aviation Institute, Volokolamskoe shosse, 125871 Moscow, Russia.
Presenting Author: W. Gawalek
Bulk blocks of melt textured YBCO are used to compose rotors for electric motors and to construct low loss superconducting magnetic bearings for fly wheels. A batch process for the production of single domain blocks with different shape and size was developed: Cylindrically shaped blocks with 30 mm and 45 mm in diameter and quader shaped blocks with 35 mm edge (all 17 mm in thickness) are prepared in a batch process with 30 respective 16 samples in one run.
In small samples critical current densities up to 6.104 A/cm2 are measured by vibration sample magnetometry. But there are indications of reduced critical current densities over full sample dimension caused by macroscopic inhomogeneities in thickness, as well as subgrain boundaries and cracks in lateral direction.
The magnetic material quality is given by the current load, the product of critical current density and diameter of superconducting current loop in the single domain (equivalent to the magnetic energy storage capability of the single domain). In practise the magnetic quality of single blocks is controlled by zero field cooled levitation force measurement of every sample and field mapping. First criterias are proposed for the standardisation of magnetic material quality. Bulk cryomagnetic elements for superconducting bearings and electric motors are assembled by cutting and bonding crystallographic oriented parts of sinlge domain blocks.
The produced elements were tested in electric hysteresis and reluctance motors and in low loss circumferential beared fly wheels. Electric reluctance motors with output power up to 38 kW are constructed in OSWALD Electromotors Company Miltenberg/Germany and MAI Moscow. A flywheel with 850 Wh kinetic energy storage capacity at 10 kW power was constructed at TU Braunschweig and a high power fly wheel (2 MW) for local energy tuning has been concepted.
*Work Supported by the German BMBF under contract 13N6854
2D2.6 High Temperature Superconductor Levitation Bearings for Space Application
Ki B. Ma, Quark Chen, Yevgeniy V. Postrekhin, Hong Ye, Yong Zhang, and Wei-Kan Chu, Texas Center for Superconductivity, University of Houston, Houston TX 77204
Presenting Author: W.K. Chu
Bulk high temperature superconductors have enabled us to construct bearings that have very little loss. As a result, mechanical devices that are highly energy efficient can be built by using these bearings. We can make the most out of these devices in energy poor environments such as space. An example of such a device is the flywheel, which can be used on board a spacecraft for attitude control or kinetic energy storage while operating under a tight energy budget. With a 19 kg. prototype flywheel, we have demonstrated the viability of the basic concepts involved and showed that the perceived advantages of low power loss or low sustenance power can actually be attained. We have also identified potential problems, mostly in the means by which we couple the flywheel to the environment, keep it going and have it be responsive to dynamic demands in a timely manner. We will discuss possible approaches to alleviate these problems without excessively compromising the energy advantages that we have gained with the adoption of superconductor magnet bearings.
2D2.7 Progress in Cryocoolers for Superconductor Applications
Ray Radebaugh, Physical and Chemical Properties Division, National Institute of Standards and Technology, 325 Broadway, Boulder, CO USA
Presenting Author: R. Radebaugh
Successful applications of superconductivity are strongly tied to the development of satisfactory refrigeration technology. In many cases it is the lack of a satisfactory cryocooler that either keeps superconductivity from reaching the marketplace or hinders its wider acceptance. Cryocooling for both low- and high-temperature superconductors is discussed and the refrigeration powers considered range from fractions of a watt up to many kilowatts. The refrigeration needs for various superconducting applications are reviewed and compared with the current state-of-the-art of cryogenic refrigeration systems. The characteristics as well as the advantages and disadvantages associated with various cryocooler types are discussed, with special emphasis on the applicability of each type for cooling superconducting devices or systems. Problems common to many cryocooler types are presented. These problems include reliability, efficiency, and cost. Recent progress in many of these cryocooler types is beginning to overcome some of these problems, but other problems remain. Some examples of superconducting systems successfully integrated with cryocoolers are illustrated, and the integration problems are discussed. Both electronic and power applications of superconductors are included.