Search

The extent to which the matrix ratio can be reduced for the rapid-heating, quenching and transformation (RHQT) [Nb.sub.3]Al wires is discussed. The non-Cu [J.sub.c] is improved by about 20% by the reduction of the matrix ratio when compared to conventional [Nb.sub.3]Al wires.

A low-matrix-ratio [Nb.sub.3]Al wire is fabricated and the effects of the rapid heating/quenching (RHQ) current and the area reduction (AR) after the RHQ process are studied. The studies have shown that the optimum RHQ current to obtain high [J.sub.c] is the current at the higher edge of the plateau region and the AR process has affected the transformation process that has determined the quality of the A-15 phase.

The synthesis of new [Nb.sub.3]Al wires with high critical current density and improved fabrication parameters, such as the heat reduction ration is being discussed. The wires exhibit conducting properties and hence can be widely used for future accelerator magnets.

The analysis describes the fundamental relationship between the BCC (body-centered cubic)-deformation, the transition temperature and the microstructure of the [Nb.sub.3]Al wires. The results prove that the transformation temperature has a tendency of monotonic decrease along with the deformation.

The fabrication and operation of a rapid-heating, quenching and transformation (RHQT) [Nb.sub.3]Al insert coil generating 4.5 T at 4.2 K in 15 T back-up field are discussed. These coils are widely used as high-field magnets.

A study is conducted to enlarge a Nb/Al strand dimension to enhance current capacity of RHQT-Nb3Al further. Bcc phases could be formed even in the large cross-section rectangular strand by RHQ operation.

The microstructure and performance of DRHQ processed Nb3Al tape with internal Ag stabilizers are investigated. The results support that the staking faults should be dominant as the effective pinning center for DRHQ processed Nb3Al conductors.

An experiment is conducted to determine the critical current I(sub c) and n-values of (rapidly heating and quenching treatment) RHQT processed Nb3Al conductors at 4.2K in a wide range fields from 14.5 to 25T in relation to the microstructures obtained. The results indicate that the n-value increased monotonously with decreasing field from 25T to 18T, but got saturated to be around 35 at 4.2K in field less than 18T.

A study is conducted to develop Nb3Ga wires by using RHQ (rapidly heating and quenching) treatment which show T(sub c) = 29.7 K and B(sub c2) (4.2K) =32 T. TEM observations clarified that the composition of Nb(sub 3)Ga varies from near-stoichiometry nearby the Nb(sub 5)Ga(sub 3) phase to Ga-poor composition nearby the Nb-Ga bcc phase.

Describing a long length of RHQ operation that is done over 300m, a transformation annealing conditions that is suitable for a coil and the resultant transport properties of the long length of conductor and coils is reported. It indicates that a long-length of the RHQ processing over 300 m and subsequent Cu-cladding is uniformly performed so that a long-length of RHQT JRNb3Al conductor gets trustworthy for practical coil applications.

Reporting a new fabrication technique for Nb/Al-Ge precursor wires, using gas-atomized Al-Ge alloy powders is discussed. It is concluded that the XRD analysis, Nb-Al-Ge ternary supersaturated bcc phase is formed with A15 and Nb5(Al,Ge)3 phases in the tape specimens with 0.2 mm in thickness, when the tape specimens are RHQ-treated.

Investigating the microchemical and microstructural comparison high performance Nb3Al composites is discussed. In the final strands the variations is much less but longitudinal cross-sections revealed the residual chemical inhomogeneity extending along the strand length.

Discussing the superconducting properties and the microstructures of RHQ-processed Nb3Al wires with Cu addition fabricated by these alternative conditions is reported. This indicates a promising possibility of improvement of J(sub c) through the optimization of precursor wire configurations and RHQ-conditions.

Investigating the Cu added jelly -roll (JR) Nb/Al wire with various Nb/Al layer thickness and compositions and discussing their effect on RHQ process is presented. The cu added JR wire of Al poor composition for Nb3Al stoichiometry showed a behavior similar to the binary is concluded.

Fabrication of jelly-roll (JR) Nb[subscript3]Al superconductors is reported. A comparison is made involving Cu-added JR Nb[subscript 3]Al, Cu-added rod-in-tube (RIT) Nb[subscript 3]Al and ordinary rapid-heating, quenching, and transformation (RHQT) JR Nb[subscript 3]Al superconductors.

Stress and strain tolerance is investigated for jelly roll (JR)-processed rapid-heating, quenching and transformation annealing (RHQT) Nb[subscript 3]Al superconductors. Results are enumerated and discussed.

Rapidly heating/quenching processes were used to determine stabilization and coil performance of Nb2A1 conductors.

A study was conducted to analyze a theoretical framework of twisted multifilamentary superconducting tapes designed to carry out numerical estimations of alternating-current losses. The model supported anisotropic Ohm's law and gives the electric field-current density properties of a superconductor by a power law. Results indicated that the model supports a numerical analysis allowing a reasonable estimation of the total loss for the tape.

The temporal evolution of current and temperature distribution in multifilamentary superconductors was calculated numerically, while they are carrying the transport current and are exposed to spatially-distributed magnetic field. Thermo-magnetic instabilities in superconductors operating at commercial frequency are initiated when their AC loss becomes maximum. When the external magnetic field is distributed axially, the radial current profile is also distributed axially. This leads to additional coupling loss. In steady state, the temperature rise due to losses is negligible. Quench process has been simulated dynamically, with the external magnetic field distributed axially. During the quench process, large temperature gradient along the conductor axis appears. The magnetic and thermal diffusions along the axis improve the stability limit against thermo-magnetic instabilities.

An equivalent circuit model of multifilamentary superconducting wires is derived to examine the temporary nature of current distribution in such wires when subjected to spatially distributed magnetic fields while carrying transport currents. AC losses are also derived based on the calculated current distributions. From these, it is shown that ac losses are dependent on the axial distribution of the longitudinal component of external magnetic fields.