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The capability of the Mg[B.sub.2] rings as superconducting permanent magnets is assessed by using the trapped field experiment. The magnetic performance can be improved by considering different geometries of the ring or by applying the same magnetization method to thick cylindrical Mg[B.sub.2] superconductors, which has produced more uniform magnetic fields.

A double pancake style Mg[B.sub.2] magnet is realized by using Columbus Superconductors Cu-stabilized multifilamentary tape. The stability features of the magnet are measured either against thermal disturbance or by self quench at different temperatures and bias currents.

The design and testing of a compound persistent-pulsed magnet for Fast Field Cycling (FFC) NMR Relaxometry are discussed. The design of the magnet includes an outer superconducting magnet working in persistent mode and an inner superconducting magnet working in pulsed mode.

Various experiments and measurements are conducted to analyze the stability in the multifilamentary [MgB.sub.2] tapes.

The experiments present a magnetic characterization of the [Mg.sub.2] superconducting hollow cylinder at variable temperatures up to the critical temperature ([T.sub.c]). The analysis reveals that an increase in the temperature and in the magnetic field leads to a strong decrease in the [eta]-values.

Ansaldo-CRIS, Napoli, Italy, is developing a cryocooler-assisted cryostat for a 4 T split-coil NbTi magnet, operated in a helium bath.

A prototype of hybrid, resistive and high temperature superconductor (HTS) 1100A current leads, cooled by cryocooler, is described and discussed.

A description of the design and manufacture of a Nb3Sn 16T demountable insert solenoid for a high field testing system is provided.

A superconducting magnet with homogeneity up to 14 T at 4.2 K and a magnet bore of 74 mm has been designed and constructed. The magnet will be used as the basis for developing a 600MHz/52 mm magnet system for NMR spectroscopy. The magnet has been built using 2 Nb3Sn and 4 NbTi coils, which generates the main field of 14.1 T at 100 A. It can be operated in either persistent or driven mode. The magnetic field decay has been measured to be 0.1 ppm/hour.

The bulk superconductors can be used as permanent magnets of very high magnetic induction, provided that a feasible way of magnetization is identified and that the superconducting material can withstand the magnetic forces induced by high trapped fields. Here it has been considered as superconducting permanent magnet a bulk MgB2 ring, obtained by the Reactive Liquid Infiltration (RLI) process. This material offers several advantages with respect to the well known YBCO textured material, even if its application temperature will be far lower, around 20-30 K. First of all, MgB2 does not require grain orientation to reach enough current density, it can be produced in a quite straightforward way, it is lightweight and it is mechanically robust. To magnetize the MgB2 ring, we have applied a DC magnetic field with a superconducting magnet, using a step wise, field cooling type, procedure. The induced magnetization of the bulk MgB2 ring, at 4 K, is around 2 T in its vicinity. It has been verified that the magnetization is very stable during the time and it can withstand also AC disturbances of several Hz in frequency. [ABSTRACT FROM AUTHOR]

In order to investigate the quench behavior of conduction cooled MgB2 magnets, a 100 mm inner bore diameter, 0.84 T at 20 K magnet has been built and tested. The test magnet consists of 4 double pancakes wound with the MgB2/Ni-Cu-Fe tape produced by Columbus. Each coil is cooled by means of a 2 mm thick copper disk placed during winding at the middle of the double pancake; after winding the double pancakes have been separately epoxy impregnated. Several experiments have been performed inducing a local transition in the coil by means of a controlled heater placed on the double pancake surface. The propagation of the normal zone has been monitored by means of 8 voltage probes positioned along the tape during coil manufacturing. Each voltage probe detects the voltage drop across a tape length of 30 mm. The experiments have been performed at different temperatures while keeping the magnet current constant during quench. In the paper we report an analysis of the quench propagation velocity measurements and a numerical investigation of the thermal and electrical behavior of the magnet. [ABSTRACT FROM AUTHOR]

We have analyzed the behavior of a 10 cm long straight piece of MgB2 copper stabilized multifilamentary tape, manufactured by Columbus Superconductors, in a nearly adiabatic condition. The tape was biased at different current values as a function of either the temperature or the induced heat disturbances at fixed temperatures. From the analyses of the voltage increase, recorded from voltage taps placed at known positions, we estimated the highest temperatures which give rise to a quench of the tape at constant values of the current bias. We also measured the minimum energy triggering the quench at fixed values of current bias and temperature. The voltage taps have also been used for homogeneity check of the physical properties which rule the thermal runaway in the tape. The voltage-versus-time curves in different sections of the tape also provide information about the quench propagation speed as a function of the hot spot energy and the temperature. Due to the composite nature of the tape, made of nickel, iron, copper, and MgB2, to perform simple FEA computation we modeled the tape with a one dimensional single wire with averaged value of the physical quantities involved in the Joule heat generation and thermal conductivity. [ABSTRACT FROM AUTHOR]

DC magnetic fields have been applied to a superconducting hollow MgB2 cylinder of relatively large dimensions (dext/int = 48/44 mm, h = 31 mm), produced by reactive Mg liquid infiltration (RLI) process. Such a kind of full dense cylinder has no discontinuity in its shape, at difference with other HTS textured cylindrical objects, and it represents a prototype of a larger one that can be applied in many electromechanical applications, like bearing, or pure magnetic application, like shielding. The aim of the experiments is to verify its shielding ability at low fields and the maximum trapped fields, when higher field are applied. The measurements are performed at variable temperatures from 13 K up to Tc. The magnetic field values, measured by Hall probe located at the center of the cylinder, dependent on the various cooling regimes (either Zero Field Cooling (ZFC) and Field Cooling (FC)) and on the presence of a background external magnetic field. The trapped fields dependence from the temperature and background field is reproduced by a simple model of the current distribution and with an analytical expression of Jc (B,T). It was possible also to describe the transition of the superconducting cylinder to the normal state, induced by flux jumping, on a base of a phenomenological model with two process having different time scale. [ABSTRACT FROM AUTHOR]

The bulk MgB2 material shows very promising characteristics to be applied in many AC devices, i.e. as electric motors, as magnetic field screening apparatus or as variable inductor or resistor for Fault Current Limitation. In all these cases the evaluation of supercurrents persistency and of the AC losses represents the first practical issue to be addressed. We report on the evaluation of these characteristics on very high density MgB2 bulk materials, obtained by reactive liquid Mg infiltration of Boron powders preform. Varying the granularity of the original Boron powders, bulks of very different grains size distribution are produced that show different current carrying capability in magnetic field and temperature, indicating a different flux structure and dynamics. Performing AC susceptibility analysis in the low frequency range, the losses have been evaluated on several shapes of the probe materials from the cylindrical one to the slab one type and for several temperatures below Tc. For ring type samples the screening effect of the superconducting currents has been evaluated, in presence of static and variable magnetic fields. The results have been interpreted in term of the critical state model, evidencing the large effects of the thermal instability erasing from the thickness of the samples. [ABSTRACT FROM AUTHOR]

DC magnetic fields have been applied to a superconducting hollow MgB2 cylinder of relatively large dimensions (dext/int = 48/44 mm, h = 31 mm), produced by reactive Mg liquid infiltration (RLI) process. Such a kind of full dense cylinder has no discontinuity in its shape, at difference with other HTS textured cylindrical objects, and it represents a prototype of a larger one that can be applied in many electromechanical applications, like bearing, or pure magnetic application, like shielding. The aim of the experiments is to verify its shielding ability at low fields and the maximum trapped fields, when higher field are applied. The measurements are performed at variable temperatures from 13 K up to Tc. The magnetic field values, measured by Hall probe located at the center of the cylinder, dependent on the various cooling regimes (either Zero Field Cooling (ZFC) and Field Cooling (FC)) and on the presence of a background external magnetic field. The trapped fields dependence from the temperature and background field is reproduced by a simple model of the current distribution and with an analytical expression of Jc (B,T). It was possible also to describe the transition of the superconducting cylinder to the normal state, induced by flux jumping, on a base of a phenomenological model with two process having different time scale. [ABSTRACT FROM AUTHOR]