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Abstract: In coaxial magnetic brakes, the changing field produced by movement of a solenoidal magnet induces a current in the wall of a conductive tube. The interaction of the field and current leads to a repulsive force that slows the motion of the magnet. For brake applications that require high force density, melt-textured YBCO is a clear choice of material for the magnet because it can carry high currents at a given field and temperature, and is inherently capable of operating in persistent current mode. We present calculations of the performance of this type of brake as a function of magnet current density for catch tubes composed of aluminum and titanium. These results are validated with low speed (20m/s) tests. Calculations indicate that melt-textured magnets can decelerate projectiles with a mass of 1kg from 2000m/s to rest in distances on the order of 10m. This suggests that this type of brake is suitable for use in hypervelocity experiments, which sometimes requires nondestructive deceleration of projectiles for diagnostic purposes. [Copyright &y& Elsevier]

Magnesium Diboride has a great potential for magnet applications in many areas such as high energy physics, Mill, and space-related projects. The main goal of our ongoing research effort is to study magnet design, winding process, and magnet testing. Last year, in a 14 cm bore solenoid we reached a central magnetic flux density of 1 tesla at 16K with almost 500 m of commercial multi-filament tape. In order to design appropriate quench detection and protection systems, it is important to define the quench propagation characteristics in solenoids made with this superconductor. In this work we show our experimental activity, from winding to testing, with a 14 cm bore solenoid made with commercial multi-filament MgB2 tape. In particular we address a quench propagation study on a coil made with 2 m of the same tape. [ABSTRACT FROM AUTHOR]

Many efforts have been made to improve the current carrying capability of Y1Ba2Cu3O7 (YBCO) films by introducing pinning centers using a variety of techniques. In this study, we have succeeded in producing Y2O3, BaZrO3 and Sm doped YBCO films for the development of coated conductors by a metal-organic deposition method using trifluoroacetates (TFA-MOD). Jc exceeding 5 MA/cm2 at 77 K and self field was obtained in Y2O3 doped YBCO film. Also it was found that YBCO films with Sm substituting for Y have shown an improved critical current density characteristic over a wide range of magnetic fields. A Jc of 0.25 MA/cm2 at 3 T and 77 K was obtained which is more than 10% of the zero-field Jc. Similar results were obtained in BaZrO3 doped YBCO films. Additionally, TEM analysis was performed to study the microstructures and the pinning mechanisms. The results indicate that significant enhancement of self-field and in-field Jc of Y2O3, BaZrO3 and Sm doped YBCO films may be due to introducing nano-scaled Y203particles, nano-scaled 90° rotated Y1/3Sm2/3Ba2Cu3O7 domains and BaZrO3 nanodots by different chemical doping, respectively. This indicates that chemical doping is a promising approach for enhancement of current carrying capability of YBCO coated conductors. [ABSTRACT FROM AUTHOR]

Superconducting coils with different dimensions were manufactured via a wind-reaction process by using Fe-sheathed MgB2 wires, which were fabricated using the powder-in-tube method and ultra-fine starting precursors. Very good grain connectivity as well as high core density was obtained in Fe-sheathed wires and tapes. At 20 K and self-field, the critical current of the coil with ID 12 mm and 12 turns is 360 A, which is equivalent to the Jc of 1.8 × 105 A/cm². At 6 Tesla external magnetic field and 4.2 K, the coil with ID 14 cm and 10 turns possesses the Jc of 1 × 104 A/cm². In-field current carrying capability of MgB2 wires and tapes were further enhanced by Ti additive. These results demonstrate the potential of MgB2 superconducting wires and tapes for large-scale applications. [ABSTRACT FROM AUTHOR]

A large number of melt-textured Y/sub 1/Ba/sub 2/Cu/sub 3/O/sub 7-x/ disk-shaped levitators have been manufactured using a seeding technique. Since DC transport current measurement is only capable of characterizing small samples, we have developed a system for measuring the component of the trapped field perpendicular to the surface of the disk (For simplicity, it will be called "trapped field".) and levitation force. The testing system is capable of measuring the distribution of magnetic field as well as the levitation force at the surface of the levitator in a relatively short time period. The magnetic field mapping can also be used to detect the granular microstructure in the levitators. The trapped magnetic fields of these levitators range between 0.45 and 0.65 T, and levitation forces are from 25 and 35 N. Also, the levitation force and the maximum trapped field values are found to correlate with each other. [ABSTRACT FROM PUBLISHER]

Ti-sheathed MgB2 wires doped with different amount of TiC nanoparticles were investigated. X-ray diffraction pattern suggested the existence of TiC0.59 phase and carbon incorporation into MgB2 lattice to form Mg(B1-xCx )2. Strong enhancement of in-field current carrying capability was observed on 2.5% TiC doped sample. The temperature effect was also studied. It was found that 850°C was the optimized annealing temperature. [ABSTRACT FROM AUTHOR]

A study of field trapping by the incomplete Meissner effect was performed on YBa2Cu3O7-x at 77 K on both sintered and oriented grain samples. Fields of up to BT=1280 G have been trapped in small, oriented grain, planar samples. Circulating persistent current densities of up to 4800 A/cm2 are calculated. Based on these values hollow cylinders of 2 cm i.d. will trap fields of 6000 G. Initial creep is about 10%/week for both types of samples. Creep rate varies as (BT/BT,max)2. BT, due to an external field B0, is BT∝(1-e-cB0/BT,max). Lamination and mosaic assembly steps for producing practical magnets have been performed. [ABSTRACT FROM AUTHOR]

Abstract: The possibility of growing large single domain YBCO solenoids by the use of a large seed has been investigated. There are two known methods for producing a similar solenoid. This first is a conventional top seeded melt growth process followed by a post processing machining step to create the bore. The second involves using multiple seeds spaced around the magnet bore. The appeal of the new technique lies in decreasing processing time compared to the single seed technique, while avoiding alignment problems found in the multiple seeding technique. By avoiding these problems, larger diameter monoliths can be produced. Large diameter monoliths are beneficial because the maximum magnetic field produced by a trapped field magnet is proportional to the radius of the sample. Furthermore, the availability of trapped field magnets with large diameter could enable their use in applications that traditionally have been considered to require wound electromagnets, such as beam bending magnets for particle accelerators or electric propulsion. A comparison of YBCO solenoids grown by the use of a large seed and grown by the use of two small seeds simulating multiple seeding is made. Trapped field measurements as well as microstructure evaluation were used in characterization of each solenoid. Results indicate that high quality growth occurs only in the vicinity of the seeds for the multiple seeded sample, while the sample with the large seeded exhibited high quality growth throughout the entire sample. [Copyright &y& Elsevier]