It has been shown that the highest critical currents in fine filament NbTi conductors are obtained when the filaments are closely spaced. 1 However, the filaments in a composite with a high purity copper matrix tend 10 be coupled via the "proximity effect" as the filament spacing is reduced leading to large magnetization ai low fields. To reduce the "proximity" coupling, trial billets of NbTi have been fabricated with Cu-30% Ni matrix, Cu-0.3% Mn matrix and one with a Ni barrier around the

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... ents. Wires drawn from these billets have shown that this interfilamcnt coupling can be suppressed for very small filament separations. A full sized commercial billet with Cu-0.5% Mn matrix demonstrates thai high J c conductors with filament size -1-5 |im can be fabricated which show no interlilameiil coupling at low fields.