  We report non-Cu critical current densities of 4.09 * 10^9 A/m^2 at 12 T and
2.27 * 10^9 A/m^2 at 15 T obtained from transport measurements on a Ti-alloyed
RRP Nb3Sn wire after irradiation to a fast neutron fluence of 8.9 * 10^21 m^-2.
These values are to our knowledge unprecedented in multifilamentary Nb3Sn, and
they correspond to a Jc enhancement of approximately 60% relative to the
unirradiated state. Our magnetometry data obtained on short wire samples
irradiated to fast neutron fluences of up to 2.5 * 10^22 m^-2 indicate the
possibility of an even better performance, whereas earlier irradiation studies
on bronze-processed Nb3Sn wires with a Sn content further from stoichiometry
attested a decline of the critical current density at such high fluences. We
show that radiation induced point-pinning centers rather than an increase of
the upper critical field are responsible for this Jc enhancement, and argue
that these results call for further research on pinning landscape engineering.
