An Experiment on Demagnetization of a Trapped Magnetic Field in HTS Bulk Exposed to an Alternating and Rotating Magnetic Field

We have examined the decay characteristics of magnetized flux in a YBCO-QMG HTS bulk material in a weak changing external magnetic field with a magnitude around the penetration field. Two kinds of external magnetic field are applied to the HTS bulk. One is a rotating magnetic field with a rotating speed of 3,000 rpm, 60,000 rpm and the other is an alternating magnetic field with a frequency of 50 Hz. In order to carry out the experiment, we have utilized a stator of a conventional 3 phase induction motor with 2 poles. The external magnetic field is applied in two directions, one is parallel and the other is perpendicular to the direction of the magnetization which corresponds to the C-axis of the HTS bulk. The characteristic of the magnetized flux decay has been measured for one hour. The experimental results show that the external magnetic field higher than 30 mT allows the trapped magnetic flux density to move more easily. And, the decay of the magnetized flux by a perpendicular magnetic field to the C-axis is larger than that by a parallel magnetic field to the C-axis.