Development of Internal Tin ${\hbox{Nb}}_{3}{\hbox{Sn}}$ Conductor for Fusion and Particle Accelerator Applications

Performance improvements are needed for large-scale applications of Nb
₃
Sn, such as ITER or LHC upgrades. The highest critical current density (J
_c
) values are achieved in distributed-barrier strand made by the Restacked Rod Process, which can reach 12 T, 4.2 K J
_c
values of 3000 A/mm
²
, with high residual resistivity ratio (RRR) values. For purposes of accelerator magnet stability, it is desirable to combine high J
_c
with a small effective filament diameter ( D
_eff
) . Initial experiments show reducing D
_eff
from 80 mum to 40 mum leads to a 10% reduction in J
_c
. For fusion applications, a single-barrier design with well-spaced filaments is used to achieve the low hysteresis losses that are required. The status of our fusion strand development program is presented, including results for strand made using Nb-47 wt%Ti rods to supply Ti dopant. Such strands can reach 12 T, 4.2 K J
_c
> 1000 A/mm
²
, with losses < 1000 mJ/cm
³
.