FLUX JUMP INSTABILITIES IN A BULK BI2SR2CACU2O8+X FLUX TUBE

Flux jumping has been observed in the shielding curves of a Bi2Sr2CaCu2O8+x tube between 2.2 and 4.5K, up to +/-3T. The temperature and applied field sweep rate dependences of the flux jump field B(fj) have been examined and compared to those of conventional superconductors with good agreement. At 4.5 K a value of B(fj) = 2.94 T is found, corresponding to the slowest sweep rate at which flux jumping occurs. The temperature spikes accompanying flux jumps have been directly measured and used to estimate an effective specific heat of almost-equal-to 0.027 J K-1 cm-3. The agreement of this with a theoretical value, although much larger than other results, is taken to confirm adiabaticity. Some novel flux jumping behaviour has been observed.