James Wong

Development of APC Nb-Ti composite conductors at Supercon, Inc

Supercon has developed a unique method for the fabrication of artificial pinning center (APC) NbTi superconductors. In this process, pure niobium and titanium layers are partially diffused so as to produce a superconductor/normal structure that will provide flux pinning at final conductor size. No precipitation heat treatments are required. Process development has resulted in Conductors with filament diameters as small as 6 and as large as 90 microns. Excellent conductor ductility and J/sub c/ performance have been demonstrated. Supercon APC conductor has been utilized in solenoid, model dipole, and MRI magnets. An overview of the development program mill be presented along with a status report on conductor scale-up efforts.<<ETX>>

Variable composition NbTi superconductors produced by artificial pinning center process

An artificial pinning center (APC) process, that utilizes pure niobium and titanium as the starting material, has been used to manufacture NbTi superconductors. The Ti content has been varied from 45.4wt% to 59.3wt% by adjusting the relative thicknesses of the Nb and Ti sheets in the starting monofilaments. Any composition can be produced in this manner, as compared to the conventional alloy which is commercially available in only one composition. The higher Ti content is designed to improve critical current density (J/sub c/s) in the low field range (<5T) and lower raw material costs, thus reducing the overall cost to the end user. The APC process does not suffer from the poorer ductility of the conventional NbTi approach when utilizing higher Ti content alloys. The new conductors would be suitable for applications such as magnetic resonance imaging (MRI), superconducting magnetic energy storage (SMES) and detector magnets.

High energy physics conductor scale-up progress of the Supercon artificial pinning center process

The Supercon APC process is briefly reviewed. Process parameters requiring optimization for commercial production are discussed. Issues involved in successful monofilament and multifilament billet size scale-up the APC process for HEP composites, nominally 6 /spl mu/m filaments and composite diameters <1 mm, are presented. The Supercon APC composite piece length and mechanical properties are excellent. The present best composite J/sub c/ results are presented.<<ETX>>

Development of APC NbTi superconductors with internal high purity aluminum stabilizer

It has long been known that high purity aluminum is superior to copper as a stabilizer for NbTi conductors, due primarily to its low density and excellent low temperature thermal and electrical conductivity. Unfortunately, it is difficult to co-process high purity aluminum with conventional NbTi conductors due to mechanical and diffusional problems caused by precipitation heat treatment, Supercon NbTi artificial pinning center (APC) material makes it possible to eliminate these problems. The concept has been demonstrated in APC composites containing /spl sim/15% high purity aluminum by volume. The recent development effort will be described and the results of mechanical and electrical testing will be given.

Development of a Nb/sub 3/Sn superconducting strand with tie-processed Nb surface coating to limit inter-strand eddy currents in cables

ITER/TPX-type bronze-route Nb-coated Nb/sub 3/Sn strands were successfully fabricated using a co-processing technique as an alternative to the existing hard chrome plating method. Results show that a continuous Nb layer as thin as 2-3 /spl mu/m can be formed on the surface of TPX/ITER strands during strand processing. This Nb coating prevents the superconducting strands in a Cable-in-Conduit (CIC) conductor from sintering during Nb/sub 3/Sn reaction heat treatment. It was demonstrated that the Nb surface coating does not degrade the residual resistance ratio (RRR) of the Cu stabilizer in the strand as well as the critical current density in superconducting filaments. The additional magnetization hysteresis loss due to the Nb surface coating is negligible when compared to the loss from Nb/sub 3/Sn filaments in the strand.<<ETX>>