Variation of ${(J_{\rm c}/J_{{\rm c}0})}_{\max}$ of Binary and Ternary Alloyed RRP and PIT $\hbox{Nb}_{3}\hbox{Sn}$ Wires Exposed to Fast Neutron Irradiation at Ambient Reactor Temperature

The variation of
T
_c
and
J
_c
for a series of binary and ternary alloyed Nb
₃
Sn wires of the RRP and PIT type has been investigated after fast neutron irradiation (E>;0.1 MeV) at the TRIGA reactor in Vienna up to a fluence of φt = 1.4 × 10
²²
m
^-2
. In contrast to Ti alloyed bronze route Nb
₃
Sn wires, where a maximum is observed at around 0.4 ×10
²²
m
^-2
, it was found that the maximum of (
J
_c
/
J
_c0
) versus φ
t
in the present ternary alloyed wires was still not reached. A comparison with an earlier study on bronze route wires at RTNS-II shows that the variations of
T
_c
versus φ
t
and
J
_c
versus φ
t
do not scale: a substantially higher
J
_c
value is now observed for the same
T
_c
value. The degree of atomic ordering being comparable, the shift of the maximum of
J
_c
/
J
_c0
with fluence is attributed to radiation induced “defect clusters.” Two observations are used for explaining the observed effect: (a) a shift of (
J
_c
/
J
_c0
)
_max
toward higher fields, observed for binary bronze wires with higher Sn contents and (b) by calorimetry, the average of the
T
_c
distribution in the filaments of RRP and PIT wires is found to occur at values up to 1.5 K higher than in bronze wires. The present data suggest that the effect of “defect clusters” is higher for wires with higher average Sn contents.