Properties of multifilamentary Nb3Sn conductors

Measurements on Nb
3
Sn multifilamentary conductors show that normally a degradation of the transition temperature T
c
and of the critical current I
c
occurs as a result of the compressive strain exerted by the bronze on the Nb
3
Sn layers when cooling down. When tensile stresses are applied, therefore, an increase of the I
c
up to a maximum value is observed at first and then the I
c
begins to decrease. These compressive strains are favourable factors when the conductor is subjected to tensile and bending loads. A coil reacted after winding produces a flux density of 12 T in a 7.5 T background field. The measured I
c
values were 10 % higher than in short samples. A coil wound with pre-reacted conductors produces a flux density of 13 T in an 8 T background field and, with an insert coil in the 55 mm bore of this magnet, 14.5 T has been measured.