AC Magnetization Loss of a YBCO Coated Conductor Measured Using Three Different Techniques

In-field ac losses were measured on a 2 G YBCO tape by three different methods; these consisted of an M(H) loop (inductive) based method as well as two different calibration-free approaches. For the M(H) loop-based method the sample was placed inside a pick-up coil connected in series with, and in opposition to, a compensation coil. The voltage developed in series across these two coils was directly proportional to the magnetic moment of the sample. AC loss was determined from the area of the hysteresis loop generated under an externally applied cyclic field. The two separate calibration-free methods used a lock-in amplifier-based technique. The first of these used a pick-up coil wound in parallel with the ac magnet winding. Two identical systems were used, each containing an ac magnet equipped with a measuring coil. One of the magnets contained the sample and the other one was left empty. The second calibration-free method measured components of the sample´s magnetic moment in a transverse ac magnetic field. Here the sample was placed inside an ac magnet; two pick-up coils were placed outside the magnet. The ac magnet, which is rectangular in shape, has an aspect ratio such that a homogeneous field is produced in the sample space and almost no stray fields are present in the pick-up coils. To measure ac loss, a z-component of the magnetic moment of the tape is determined using a dipole approximation. The AC losses for a coated conductor in fields of amplitude up to 0.14 T applied perpendicular to the broad face of the tape were measured from 36 Hz-75 Hz in a liquid nitrogen bath using all three methods. These results were compared, and a satisfactory agreement between all three methods was obtained.