AC MAGNETIC-FIELD PENETRATION INTO THIN CERAMIC DISKS WITH DIFFERENT GRANULE SIZES

We investigated the penetration of both alternating and direct magneti c fields into a series of thin ceramic disks produced from the same YB aCuO powder but with different granularity; We used hall probe, tiny m easuring coil and autodyne generator to cover the frequency range from DC to 19 MHz. The time dependence of penetrated flux during AC field cycle was compared with the result of calculation. Basing on a critica l state model with frequency dependent critical current we have determ ined the appropriate The magnetic field amplitude and frequency depend ence of it was studied and discussed. The effect of exceeding of magne tic flux time derivative near the disk center comparatively with that of the external field was observed for high AC field amplitudes.