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In order to investigate the possibility of using superconducting magnets for Fast Field Cycling (FFC) NMR Relaxometry, a NbTi magnet able to achieve high field variation rates in a constant background field has been designed and tested. The design layout consists in an outer superconducting magnet working in persistent mode and an inner superconducting magnet working in pulsed mode. The layout of the inner magnet has been optimized taking into account field strength, field homogeneity, stray field and inductive coupling with outer magnet. A demonstration pulsed magnet has been tested in a background field, achieving the main desired working features.

The adoption of High Temperature Superconductors (HTS) tapes is becoming a suitable and interesting alternative to copper for windings in transformers, thanks to the improvement in performance and the lowering of costs. Of course, optimized designs, different with respect to usual layouts, must be considered, due to the additional requirements of HTS tapes, such as minimization of orthogonal magnetic fields and consideration of additional losses in the HTS. In the framework of a scientific cooperation among some Italian Universities and private companies, a test model for a 10KVA transformer with HTS secondary windings has been developed, and validated against a demonstrative prototype, manufactured during the project. In the paper, the device model performance is assessed, with particular care to the HTS losses modeling, and some comparisons to the experimental results are presented.

Power transformers based on High Temperature Superconductors (HTS) technology are an appealing promise for several practical applications. The present designs still leave wide margins of possible improvement in terms of both layout optimisation and introduction of new technologies. In the framework of a technical-scientific cooperation among scientific and industrial subjects, a 10 kVA single-phase transformer was designed and manufactured, using copper for primary windings and BSCCO-2223 HTS tape for secondary windings. The layout has been optimized taking into account the particular characteristics of BSCCO tapes, in particular their AC losses, and the usual figures (stray flux, Joule and iron losses, weight and overall footprint) considered in transformers design. The prototype has then been realized and characterized, using general as well as specific tests. The performance of the device has been evaluated and compared with numerical calculation. In the paper, an overview of the device design and manufacturing will be presented, together with a critical comparison between computed and measured performance.

"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."

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 straight forward 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.

We have analyzed the behavior of a 10 cm long straight piece of 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 , 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.

The magnetic shielding produced by superconducting tubes was of applicative interest in high energy physics apparatus. Except several attempts with LTS materials, up to now no HTS material has been used for this application, partly due to the low current capability and partly to the poor mechanical properties of the conventional bulk cuprates. An alternative, among the Medium Temperature Superconductor (MTS) material is represented by MgB2 in bulk form. This material can be quite easily produced at high density by the reactive liquid Mg infiltration route, generating tubular bodies of various shape and good mechanical strength. The shielding efficiency in several tubular MgB2 objects has been tested at 4.2 K, applying DC and AC fields and the criticality of the thermal instability due to flux jumps of the superconducting manufacts has been evidentiated. The possibility to shield field larger than 1 T has been demonstrated.

The bulk MgB/sub 2/ 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 MgB/sub 2/ 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.

Within the Italian project for the development of 1 MJ/1 MW SMES, Ansaldo-CRIS and CESI have been involved in the design and manufacturing of 1100 A resistive/HTS current leads conduction cooled by a closed cycle refrigerator. Main design and technological problems concern the achievement of electrical insulation between cryocooler and current leads at the voltage level of 6 kV together with a thermal contact good enough to keep the upper part of the HTS material at a temperature below 70 K, when the cryocooler temperature is 60 K and about 100 W is the thermal load. Thermal transport properties of electrical insulating materials as thin sheet placed between copper massive plates have been measured as a function of temperature and hence, according to the measured thermal performances, the area for thermal contact with the cryocooler has been suitably dimensioned. Mechanical structure for the whole current leads has been designed and manufactured. Final assembly of resistive section has been completed. Results about the achieved lead performances are presented and discussed.

A cryocooler assisted cryostat for a 4 T split-coil NbTi magnet operated in liquid helium bath is under development at the ANSALDO-CRIS. A two stage GM cryocooler (1st stage 15 W @ 45 K, 2nd stage 5 W @ 15 K) is used for the cooling of two radiation shields at temperatures less than 45 K and 15 K respectively. For magnet charge, a couple of 100 A vapor cooled HTS current leads, based on Bi-2223/AgAu tapes, operates between the 1st stage of cryocooler and the helium bath. AlN plates have been used to obtain a good thermal contact electrically insulated between HTS lead and cryocooler. The developed configuration allows to eliminate liquid nitrogen cooled radiation shields and to minimize static liquid helium consumption. Calculated and measured system performances are compared.

In the framework of the characterization and quality control of the Nb/sub 3/Sn strand for the manufacturing of the ITER (International Thermonuclear Experimental Reactor) Model Coils, the Applied Superconductivity Laboratory at ENEA (Ente per le Nuove Tecnologie Energia Ambiente) Frascati decided to increase the background field of its facility for I/sub C/ measurements from 14.5 T up to 16 T. The upgrade was obtained by an insert coil designed and manufactured by Ansaldo CRIS (Consorzio Ricerche Innovative per il Sud), Naples, Italy. The Nb/sub 3/Sn strand provided by Europa Metalli is an internal tin diffusion high critical current density 0.90 mm wire with the following characteristics: I/sub C/=160 A@4.2 K, 16.5 T; Cu/nonCu ratio 1. The solenoid (outer diameter 80 mm, inner bore 37 mm) was manufactured by winding the insulated Nb/sub 3/Sn strand onto an AISI 316L, stainless steel former and reacting it up to 650/spl deg/C. A self consistent unit has then been assembled, consisting of the insert module, mechanical structure and separate current leads. This allows easy installation of the insert inside the 14.5 T, 80 mm background magnet; removal is possible also in cold conditions without damage. The operational current (113.7 A) was achieved at the first energization with a maximum field on the windings of 16.49 T. This test has been done connecting electrically in series the background magnet and the insert, being therefore limited by the maximum allowable current (114 A) in the background magnet. Further tests with an independent current supply to the insert will be carried out to evaluate its performance limits.

The feasibility of a 5 T magnet by using Bi-2223/Ag tapes at 30 K has been investigated. Preliminary computation demonstrates that the target is attainable by assembling 20 double pancakes manufactured by co-winding two Bi-2223/Ag tapes having overall cross-section of 0.25 × 3.5 mm 2 and 25% fill factor, being the expected operating current about 200 A. The pancakes located at the edges are the most critical because the component of the magnetic field orthogonal to the tape surface is large enough to strongly depress J c . To overcome this problem the edge pancakes could be fabricated by using Bi-2223/Ag tapes with new concept design (e.g. with oriented filaments).

A high homogeneity magnet, up to 14 Tesla at 4.2 K with magnet bore of 74 mm was developed. This magnet is the starting point in order to develop a 600 MHz/52 mm magnet system for NMR spectroscopy. The field homogeneity is better than 5 ppm over 1 cm diameter sphere volume without any shim-coils. The magnet can be operated in persistent mode and driven mode. The required magnetic field decay rate is 0.1 ppm/hour. A quench analysis has been studied. Magnetic and structural analysis has been performed. Main data of the magnet system, phases of technological development and test results are reported in this paper.

High stable trapped fields in bulk superconductors can be useful applied in many electrotechnical applications, as i.e. for motor/generators, for MRI systems or for magnetic separation devices. The HTS bulk materials appear as the matter of choice to this purpose and many attempts have been done on melt textured cuprates tiles, at temperatures up to 77K, applying constant magnetic fields or pulsed magnetization methods. Even if the pulse magnetization is far less effective than the DC magnetization in the trapping capability, it appears as the most friendly technique in practical devices. So we have studied the effects of the pulsed technique, applied to a bulk MgB2 cylinder: a very promising device in view of the feasibility of similar much larger manufacts. To this purpose we have used a copper solenoid to magnetize the MgB2 cylinder, with both cylinder and solenoid conductively cooled by a cryorefrigerator, in the range of temperatures between 5 and 20 K. This simple cryogenic arrangement can be repres...

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.