Summation and Saturation Behaviour of the Volume Pinning Force in Neutron Irradiated V3Si

Neutron irradiated V3Si is used as a model system for the investigation of the dependence of the volume pinning force on the defect structure in A15 superconductors. The dislocation loop concentration determined by TEM is varied within three orders of magnitude. Up to the highest concentration the system is still dilute, but there is absolutely no field region where the volume pinning force is proportional to the concentration of pinning centres as predicted by the summation models and proved in low x-material like Nb. This unexpected behaviour is accompanied by the peak effect and by a saturation of the volume pinning force in the whole field region at a fluence of 1018cm−2. The explanation is based on the threshold criterion which is not satisfied in these microstructures.