Three (MgB) (SnO) samples with ranging from 0 to 5 wt% were prepared by the route to study the effect of tin dioxide additions on the superconducting properties of MgB bulk materials. All of the reacted samples were slightly Mg deficient although the starting Mg:B precursor powder ratio was 1:2. A heat treatment (HT) temperature of 700 °C with a dwell time of 30 min was used. XRD results showed evidence of peak shifts for MgB phases with SnO addition. The magnitude of the -axis lattice constant change (0.361 ± 0.075 %) calculated for the 3 wt% doped samples is comparable in magnitude to that seen previously for the C-doped MgB bulks which exhibited enhanced . The upper critical fields ( ) and the irreversibility fields ( ) were measured resistively in fields up to 14 T at 5 K to . The best value at 20 K (15.2 T based on extrapolation) was seen for sample IS3 (x = 3 wt%), and was comparable to the best values (≈ 15 T at 20 K) seen for C-doped MgB bulks. IS3 had a corresponding = 10.8 T (20 K). The superconducting transition temperature ( ) appeared to increase slightly with doping, although within the range of error bars (37.4 K to 37.6 K for 1.6 T increase at 20 K), in contrast to C doping which is accompanied by a significant decrease in (39 K to 36 K for 3.8 % C doped MgB bulk). We attribute the observed increase in both and for SnO-additions to lattice strain caused by the introduction of precipitates within the grains.

The influences of strand twisting and bending (applied at room temperature) on the critical current densities, , and -values of MgB multifilamentary strands were evaluated at 4.2 K as function of applied field strength, . Three types of MgB strand were evaluated: (i) advanced internal magnesium infiltration (AIMI)-processed strands with 18 filaments (AIMI-18), (ii) powder-in-tube (PIT) strands processed using a continuous tube forming and filling (CTFF) technique with 36 filaments (PIT-36) and (iii) CTFF processed PIT strands with 54 filaments (PIT-54). Transport measurements of and -value at 4.2 K in fields of up to 10 T were made on: (i) PIT-54 after it was twisted (at room temperature) to twist pitch values, , of 10-100 mm. Transport measurements of and -value were performed at 4.2 K; (ii) PIT-36 and AIMI-18 after applying bending strains up to 0.6% at room temperature. PIT-54 twisted to pitches of 100 mm down to 10 mm exhibited no degradation in and only small changes in -value. Both the and -value of PIT-36 were seen to be tolerant to bending strain of up to 0.4%. On the other hand, AIMI-18 showed ±10% changes in and significant scatter in -value over the bending strain range of 0-0.6%.

A prototype compact annulus YBCO magnet (YP1070) for micro-NMR spectroscopy was constructed and tested at 77 K and 4.2 K. This paper, for the first time, presents comparison of the 77-K and 4.2-K test results of our annulus magnet. With a 26-mm cold bore, YP1070 was comprised of a stack of 1070 thin YBCO plates, 80-µm thick and either 40-mm or 46-mm square. After 1070 YBCO plates were stacked ''optimally'' in 214 groups of 5-plate modules, YP1070 was ''field-cooled'' at 77 K after being immersed in a bath of liquid nitrogen (LN) with background fields of 0.3 and 1 T and also at 4.2 K in a bath of liquid helium (LHe) with background fields of 2.8 and 5 T. In each test, three key NMR magnet field-performance parameters-trapped field strength, spatial field homogeneity, and temporal stability-were measured. At 4.2 K, a maximum peak trapped field of 4.0 T, equivalent to 170 MHz H NMR frequency, was achieved with a field homogeneity, within a |z| < 2.5 mm axial space, of ~3000 ppm. YP1070 achieved its best field homogeneity of 182 ppm, though at a reduced trapped field of 2.75 T (117 MHz). The peak trapped fields at 4.2 K were generally ~10 times larger than those at 77 K, in direct proportion to ~10-fold enhancement in superconducting current-carrying capacity of YBCO from 77 to 4.2 K. Temporal stabilities of ~110 and ~17,500 ppm/h measured at 77 K, with trapped fields respectively of 0.3 and 1 T, show that temporal stability deteriorates with trapped field strength. Also, temporal enhancement of trapped fields at 4.2 K was observed and reported here for the first time.

We report on electrical transport measurements at high current densities on optimally doped YBaCuO thin films grown on vicinal SrTiO substrates. Data were collected by using a pulsed-current technique in a four-probe arrangement, allowing to extend the current-voltage characteristics to high supercritical current densities (up to 24 MA cm) and high electric fields (more than 20 V/cm), in the superconducting state at temperatures between 30 and 80 K. The electric measurements were performed on tracks perpendicular to the vicinal step direction, such that the current crossed between planes, under magnetic field rotated in the plane defined by the crystallographic axis and the current density. At magnetic field orientation parallel to the cuprate layers, evidence for the sliding motion along the planes (vortex channeling) was found. The signature of vortex channeling appeared to get enhanced with increasing electric field, due to the peculiar depinning features in the kinked vortex range. They give rise to a current-voltage characteristics steeper than in the more off-plane rectilinear vortex orientations, in the electric field range below approximately 1 V/cm. Roughly above this value, the high vortex channeling velocities (up to 8.6 km/s) could be ascribed to the flux flow, although the signature of ohmic transport appeared to be altered by unavoidable macroscopic self-heating and hot-electron-like effects.

In 2008, the Phase 3 program to complete a 1.3 GHz (30.5 T) NMR magnet started at the Francis Bitter Magnet Laboratory, Massachusetts Institute of Technology. It comprises two sub-phases, 3A and 3B. In Phase 3A, a 600 MHz high temperature superconductor (HTS) insert magnet (H600) will be designed, constructed, and operated in the bore of a 500 MHz low temperature superconductor (LTS) background magnet. This will be followed by Phase 3B, in which the H600 will be combined with a 700 MHz LTS background magnet to complete a 1.3 GHz NMR LTS/HTS magnet. This paper presents and discusses design issues for two conductor options for H600: BiSCCO-2223 (Bi2223) and coated-YBCO or its variants, here designated as YBCO. For each conductor option, we focused on the following issues: 1) elastic and thermal properties; 2) critical current vs. field performance; 3) splice and index heat dissipations; 4) mechanical and thermal stresses; and 5) protection.