The Effect of Thermo-Mechanical Treatments on $J_{c}(T,B)$ and $T_{cs}$ of Nb-Ti Strands

An extended database of critical current densities
J

_c
(
T
,
B
) and current sharing temperatures T
_cs
for Nb-Ti strands was obtained in this work. This data set allows one to make a more realistic forecast of the ITER poloidal field (PF) coil critical current at temperatures above 6 K and in a magnetic field of 6 T. It is found that
Jc
(4.2 K, 5 T) lies in the range from 700 to 2950 A/mm
²
, depending on the heat treatment regimes, and that J
_c
(6.5 K, 6 T) is 28 to 54 A/mm
²
almost regardless of the applied heat treatment, i.e. the microstructure does not significantly affect J
_c
(6.5 K, 6 T) under such ldquoextremerdquo conditions. It is shown, that
T

_cs
(6 T) at a current of 31.2 A, which is close to the assumed operating current for the strand in the ITER PF1&6 coils, is 6.1-6.25 K. It is shown furthermore, that the application of multiparametric functions for the description of
J

_c
(
T
,
B
) or V(I, T, B) leads to a reliable prediction of J
_c
(T, B) only in a temperature and field range, where experimental data points are available (extrapolations result in large deviations).