Study of dendritic avalanches by current noise measurements in High Tc Superconductors

Spectral noise power measurements are reported in a bulk YBa(2)Cu(3)O(7-delta) superconductor at 4.2 K to investigate the flux vortex avalanche processes originated from thermomagnetic instabilitites in an applied magnetic field up to 600 mT and in feeding current close to the critical value. 1/f(gamma) behavior is shown at frequencies below 10 Hz, gamma values range from 0.7 to 1.7. A sharp peak is observed in applied field and from these results we have obtained a cutoff frequency around 20 Hz for Lorentzian shape knee from which we estimate a mean number of 500 vortices and a mean velocity of about 20 cm/s for the average avalanche