INFLUENCE OF THE STRUCTURE DEFECTS INDUCE D BY DEFORMATION AT 4,2 K ON THE CRITICAL-CURRENT OF SUPERCONDUCTING NIOBIUM

The influence of deformation defects generated by twist deformation at 4.2 K upon field dependences of the critical current density J(c)(H) of niobium is studied. It is shown that the typical increase of J(c) v alue near H-c2 and its <<anomalous>>, drop in a relatively low-field r egion is a result of increasing now stress. The decrease in J(c) is du e to the intensification of thermomagnetic instability in the ares of localized plastic deformation (twin boundaries, rotation plasticity ar eas). As discussed earlier at these sites the superconducting transiti on temperature Te is essentially higher (by similar to 10%), and this stipulates for the running of local high-density critical current. Cha racteristics of thermomagnetic instability are estimated.