A multifilamentary Nb3Sn dipole magnet

A one meter long, 8 cm aperture dipole magnet has been constructed from prereacted Nb3Sn multifilamentary conductor. The conductor is in the form of a wide braid formed from 95 wires of 0.3 mm dia. each containing 1045 filaments of niobium in a copper-tin matrix. After braiding and compacting the conductor was heat treated to form the Nb3Sn filaments. The braid was then wound into a dipole of the ISA type using techniques similar to those employed in the construction of magnets from the more conventional NbTi braid. Voltage taps were attached to the conductor at appropriate positions so that the effect of mechanical stress could be observed at the bends of greatest curvature. The effective resistivity of the bent regions of the conductor showed a marked dependance on the bend radius varying from 7 × 10^-10ohm-cm at a radius of 0.6 cm to approx, 10^-10ohm-cm at 1.0 cm measured at a field of 3 T and a current density of 3.7 × 10⁴Amps/cm². While the bending of the conductor during coil fabrication did lead to some damage of the Nb3Sn filaments, it was not the factor limiting coil performance. The connection between the coil halves in the magnet was resistive and limited the maximum coil current to 2650 amps, well below the short sample limit. An improved method of coil interconnection is being used in future magnets in this series and should make it possible to extend the measurements to higher fields and current densities.