  The occurrence of high stress concentrations in reactor components is a still
intractable phenomenon encountered in fusion reactor design. We observe and
quantitatively model a non-linear high-dose radiation mediated microstructure
evolution effect that facilitates fast stress relaxation in the most
challenging low-temperature limit. In situ observations of a tensioned tungsten
wire exposed to a high-energy ion beam show that internal stress of up to 2 GPa
relaxes within minutes, with the extent and time-scale of relaxation accurately
predicted by a parameter-free multiscale model informed by atomistic
simulations. As opposed to conventional notions of radiation creep, the effect
arises from the self-organisation of nanoscale crystal defects, athermally
coalescing into extended polarized dislocation networks that compensate and
alleviate the external stress.
