A new class of 'powder-in-tube' Mg-B superconducting conductors has been prepared using two different methods: an in situ technique where an Mg + 2B mixture was used as a central conductor core and reacted in situ to form MgB 2 , and an ex situ technique where fully reacted MgB 2 powder was used to fill the metal tube. Conductors were prepared using silver, copper and bimetallic silver/stainless steel tubes. Wires manufactured by the in situ technique, diffusing Mg to B particles experienced ∼25.5% decrease in density from the initial value after cold deformation, due to the phase transformation from Mg + 2(β − B) → MgB 2 all with hexagonal structure.A comparative study of the intergranular current and grain connectivity in wires was conducted by AC susceptibility measurements and direct four point transport measurements. Using a SQUID magnetometer, magnetization versus magnetic field (M-H ) curves of the round wires before and after sintering and reactive diffusion were measured at 5 K and in magnetic fields up to 5 T to define the J cmag . The direct current measurements were performed in self field at 4.2 K. A comparison between zero-field-cooled (ZFC) and field-cooled (FC) susceptibility measurements for sintered Ag/MgB 2 , and reacted Cu/Mg + 2B conductors revealed systematic differences in the flux pinning in the wires which is in very good agreement with direct high transport current measurements.

Details are given for the design, construction, properties, and performance of a large, highly homogeneous magnet designed to permit whole-body magnetic resonance imaging and spectroscopy at 4 T. The magnet has an inductance of 1289 H and a stored energy of 33.4 MJ at rated field. The health of a group of 11 volunteers who had varying degrees of exposure to this field was followed over a 12-month period and no change that could be associated with this exposure was detected. A mild level of sensory experiences, apparently associated with motion within the field of the magnet, was reported by some of the volunteers during some of their exposures. A questionnaire regarding sensory effects associated with magnetic resonance scanners and possibly caused by the static magnetic field of these instruments, was given to nine respondents who had experience within both 1.5-T scanners and this 4-T scanner and to another group of 24 respondents who had experience only within 1.5-T scanners. For the sensations of vertigo, nausea, and metallic taste there was statistically significant (p less than 0.05) evidence for a field-dependent effect that was greater at 4 T. In addition, there was evidence for motion-induced magnetophosphenes caused by motion of the eyes within the static field. These results indicate the practicality of experimental whole-body body scanners operating at 4 T and the possibility of mild sensory effects in humans associated with motion within a static magnetic field. The results also indicate the likelihood of a wide margin of safety for the exposure of noncompromised patients to the static fields of conventional magnetic resonance scanners operated at 1.5 to 2 T and below.

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Engineering considerations for the production of small HT, COUS for commercial high current applications have been evaluated. Part of this study involved investigations of the conditions under which coils are wound, heat treated and potted in order to reproduce, in lengths exceeding 50 m, the critical current density (J,) which can be attained in short samples of a few cm in length. Individual pancake coils were evaluated by testing their 4.2 K superconducting current capacity in the presence of an applied magnetic fleld up to 10 T. The performance of each coil was compared to the J, capacity predicted &om short sample Jc testing on samples of a few cm length. Coils were then stacked to form prototype magnets and the field generated by the magnet was measured using a Hall Probe. L INTRODUCTION 1) PIT: Lengths of up to 250 m of PIT are now routinely produced by a conventional method. The 2212 powder is packed into a silver sheath, the ends are closed and the wire is then drawn and rolled. Typical dimensions of the PIT are 3.8 mm x 0.15 mm with a silver to superconductor ratio of 3: 1.2) DIP: Dipcoated silver tape is produced by a continuous method. Pure silver or alloy substrate tape is drawn through a slurry, dried and spooled. The substrate has a typical thiclmess of 50 pn and emerges carrying 50 -200 pn of slurry on each side. Widths are between 6 and 25 mm. Following burnout of the organic binder, the thiclmess of the coating is reduced to between 10 -50 pn, giving a silver to superconductor ratio in the range 0.5: 1 to 2.5: 1. / a) powder -in-& / Ceramic oxide superconductors may hold the key to a number of high current applications. In particular, energy storage and high field insert coils could b e f i t from a new generation of superconducting materials. Oxford Superconducting Technology, in conjunction with Oxford b) dipcoatedResearch Instruments, are developing BSCCO conductor fabrication routes with the objective of producing useful lengths of high J, conductor. SmalJ coils are being constructed by standard processes and then assembled in arrays to form larger magnets. A focal point of the development program is to determine whether degradation of C)AgSheatheddip-CWlkd short sample J, in longer lengths is predominantly chemical or mechanical in origin. This requires locating and investigating the "gW-and "poor" regions.

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