Anomalous increments of AC losses due to flux jumps

AC losses are measured applying magnetic fields of frequencies from 8.6 to 75 Hz and of 3 kG peak values to wires of Nb-60.2Ti-2.8Zr alloy mounted in slots of a bakelite bobbin. The temperature is varied between 1.9 K and the superconducting transition temperature Tc= 8.9 K using supercritical He as coolant for the higher temperature region. Anomalous increments of AC losses caused by flux jumps are observed at certain field values Hfj. Hfjis almost constant at temperatures T = 4.2 to 6 K and decreases if the temperature is reduced below 4.2 K. The temperature dependence of Hfjcan be explained qualitatively by the temperature depencence of both the specific heat and the pinning force of the sample. The quantitative difference as well as a very weak frequency dependence of Hfjand a reduction of Hfjby embedding the sample in grease may be due to the influence of the special heat transfer conditions.