Critical current of multifilamentary Nb3Sn wire in high magnetic field

The critical current of copper-stabilized multifilamentary Nb
3
Sn wire was measured in magnetic fields up to 18 T at 4.2 K, 2.85 K and 2.18 K. The conductor investigated in the experiment was fabricated by a "bronze" process. Its external diameter is 0.53 mm and it consists of 2886 filaments (5 μm dia.) in a bronze (13 wt%Sn) matrix. The measurements show that the conductor has excellent superconducting properties. For instance, J
c
(N
b
+ bronze) of the sample heat treated for 100 hours at 700°C is as follows : at 4.2 K, 8 × 10
⁴
A cm
^-2
at 10 T , 6 × 10
³
A cm
^-2
at 18 T ; at 2.18 K, 1 × 10
⁵
A cm
^-2
at 10 T and 1.5 × 10
⁴
A cm
^-2
at 18 T. The extrapolated values of Bc
2
, according to the scaling law for flux pinning, are 22 T and 23.8 T, at 4.2 K and 2.18 K respectively. Transition temperature results are also discussed.