Influence of filament spacing and matrix material on the attainment of high quality, uncoupled NbTi fine filaments

Test results are presented that show that, for optimum performance of fine-filament NbTi materials, the spacing between the filaments (S) must be a small fraction of the filament diameter (D). Colliding-beam accelerator (CBA)/fermi kit material is shown to exhibit markedly improved properties simply by using thinner-walled copper tubes, thus reducing S/D. Reduction of the interfilamentary spacing, however, enhances the possibility of electrical coupling of the filaments. The authors describe two approaches to impede the motions of the superelectrons between adjacent filaments. The first, which acts to suppress the mean free path of the electrons leads to a high-resistivity solid-solution-alloy matrix, such as CuNi. The second, employs electron-spin-flip scattering by solute ions carrying localized magnetic moments such as Mn, Fe, or Cr.