A New Measurement Method for AC Losses in Circular Disks of Superconducting Films in Perpendicular Magnetic Fields

This is the authors' abstract. We don't add key points for this paper.

An expression P=2R/sub c/V/sub L rms/H/sub a rms/ was theoretically derived for the ac power losses in a circular superconducting disk in a perpendicular ac applied magnetic field when the losses are measured by a planar circular pickup coil surrounding the disk. Here, R/sub c/ is the radius of the pickup coil, which is coplanar with the disk, and V/sub L rms/ and H/sub a rms/ are rms values of the loss voltage and applied magnetic field. This method of measuring losses has an advantage over a susceptibility technique, since the coil need not be calibrated. However, this expression is valid only for large values of R/sub c/ relative to the radius R of the disk, since the dipole approximation was used in the derivation. We experimentally evaluated the minimum value of the diameter 2R/sub c/ for which this method provided approximately correct losses. A YBa/sub 2/Cu/sub 3/O/sub 7/ disk with diameter 2R/spl ap/5.3 mm was used for the measurements. The electronically determined apparent losses at all field values decreased with increasing coil radius, and asymptotically approached a constant value for R/sub c//R>/spl sim/3.