Magnetic shielding of MgB₂ tubes in applied DC and AC field

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Performance Evaluation for a HTS Transformer

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

Normal zone propagation in a MgB2 conduction cooled test magnet

In order to investigate the quench behavior of conduction cooled 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 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 per- formed inducing a local transition in the coil by means of a con- trolled 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

Design and Test of a Compound Persistent-Pulsed Magnet for Fast Field Cycling NMR

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

HIGH DENSITY MgB2 BULK MATERIALS OF DIFFERENT GRAINS SIZE: SUPERCURRENTS INSTABILITY AND LOSSES IN VARIABLE MAGNETIC FIELDS

The bulkMgB2 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 densityMgB2 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

Stratigrafia dei depositi pleistocenico-olocenici dell’area costiera di Metaponto compresa fra Marina di Ginosa ed il Torrente Cavone (Italia meridionale): carta geologica in scala 1:25.000

In order to improve the geological and stratigraphic knowledge of the Metaponto coastal area a detailed geological survey has been performed between Marina di Ginosa (Taranto) and Cavone river (Matera). Furthermore, a facies analysis either along stratigraphic sections or on cores obtained from five continuously-cored boreholes, drilling in the Holocene and middle – upper Pleistocene deposits up to 120 m of depth, has been carried out. The outcropping deposits have been distinguished in: upper Pleistocene “sandy-conglomeratic deposits of the regressive coastal prisms” and Holocene “Metaponto plain deposits”. The first deposits are subdivided into three lithostratigraphic units. The first two units have a thickness variable up to 15 m, and are represented by sandy-conglomeratic prisms resulting from the interplay between sea-level fluctuations and regional uplift; they are referred to “sabbie e conglomerati di Policoro” and “sabbie e conglomerati di Masseria Ricotta”, showing facies features of shoreface passing upward to continental environments. The third unit, up to 2 m thick, is an “eluvial product”, made up of reddish sands with gravelly layers unconformably and discontinuously overlaying the previous deposits. The Holocene “Metaponto plain deposits” have been distinguished in: “continental deposits” and “transitional deposits”. Continental deposits are represented by mainly some meters thick fine- to coarse-grained sediments of eluvial, fluvial, lacustrine and palustrine environments. Transitional deposits are represented by some meters thick sandy and silty Holocene beach-dune systems (modern and ancient) and sandy and clayey-silty deltaic systems (modern and ancient). The buried deposits of the Metaponto coastal area have been distinguished in three units thanks to the facies analysis and mainly to the recognition of two important erosional surfaces. The lower unit (called substratum), found beginning from a depth variable from 13 m to 44 m moving seaward, is at least 76 m thick and made up of clayey-silty deposits, with interbedded sandy beds passing landward and upward to sandy and/or sandy-gravelly deposits. The lower boundary was not found, whilst the upper boundary is represented by an erosional surface (SE) highlighted by a lag deposit. The facies features of these deposits can be referred to offshore passing upward to shallow marine environments. The age is middle - late Pleistocene. The intermediate unit is bounded both on bottom and on top by erosional surfaces (SE and ST). This intermediate upper Pleistocene wedge-shaped unit, called “Metaponto buried plain deposits”, pinches out landward, passing from about 7 m to 0 m in thickness. It is made up of sandy-gravelly deposits of continental to shallow marine environments. The third upper unit erosionally overlies both the previous unit and the substratum by the ST surface. This unit is made up of sands and gravelly sands, and its thickness varies from 13 m to 48 moving seaward, and has been attributed to the progradation of a beach system, laterally linked to a deltaic system, and passing seaward to an offshore system. A lamellibranch shell yielded a not calibrated 14C age of 7.572±50 yr BP for these deposits. The overall collected data allow us to draw a geological map on 1: 25.000 scale that provides a new stratigraphic framework of the outcropping Metaponto plain deposits. Furthermore, the geological sections obtained also utilizing the boreholes allow us both to reconstruct the geometry of the buried deposits and to outline the evolutionary history of the Holocene transgressive prism along the coastal study area