Properties of an Experimental Coil Wound With YBCO Coated Conductor Carrying an AC Current With Frequencies up to 864 Hz

To study the properties of coils made out of the second generation superconducting wire, we designed, manufactured and tested an experimental double pancake coil wound with 4.2 meters of a 4 mm wide, copper stabilized YBCO coated conductor. The critical current of a short sample was 53 A at 77 K in self-field. The critical current of the single pancake coil based on the 1 V/cm criterion for the average electric field was approximately 30 A. The critical current of the complete double pancake was about 23 A. Using micro Hall probes, we measured the radial magnetic field component at the edges of the coil. The results clearly indicated the strong influence of the magnetization currents on the magnitude and distribution of the radial field component. AC losses in the coil were measured at frequencies of 54 Hz, 108 Hz, 216 Hz, 432 Hz and 864 Hz. At the critical current (16.2 A) and frequency 432 Hz the coil losses were 0.9 W. The magnetic measurements showed that the tape in the winding is exposed to a very inhomogeneous magnetic field. The experimental results of the field distribution in the winding were compared with the existing theoretical models.