DYNAMICS OF LOW-FIELD PENETRATION IN (YBA2CU3O7-DELTA)1-XAGX CERAMICS

We present experiments carried out in tubular (YBaCuO)1-xAgx samples (0 less-than-or-equal-to x less-than-or-equal-to 0.5) cooled to 77 K. An external solenoid coil generates a pulsed magnetic field in the sample. A pickup coil measures the rate of variation of the magnetic flux in the hole. The coil voltage pulse is characterized by a delay DELTA-t and two time constants tau(1) and tau(2), with tau(1) >> tau(2). The whole process of flux penetration takes place in a lapse of time which is typically of the order of a few tens of microseconds. At fixed reduced field B/B* and for two samples having the same wall thickness but different silver contents (up to x almost-equal-to 0.3), the main characteristic times appear to be correlated as DELTA-t(2)/DELTA-t(1) almost-equal-to tau(1)(2)/tau(1)(1) almost-equal-to (B*(1)/B*(2)) (rho(n)(1)/rho(n)(2)), where B* is the penetration induction (i.e. the value of the applied external induction below which no flux appears in the hole) and rho(n) the normal resistivity of the sample. These results can be essentially interpreted as a flux flow phenomenon.