AC loss study by AC susceptibility measurement in a commercial Bi:2223/Ag tape prepared by the CTFF method: H \parallel c axis and short specimen

The effect of temperature, field amplitude, frequency and orientation of the field on AC losses in a commercial Bi:2223/Ag tape prepared by the continuous filling and forming (CTFF) method has been investigated. The measurements were performed using an AC susceptometer. The experimental results show that the losses depend on field amplitude, temperature, DC field, orientation of the sample and strongly on frequency. Due to the strong dependence of AC losses on frequency, measurements were pursued at several frequencies between 20 Hz and 10 kHz at various temperatures (10, 20, 30 and 77 K). The strong frequency dependence at these low temperatures is attributed to eddy current losses and/or inter-filamentary coupling losses. At higher temperatures and low frequencies, the main contribution to AC losses comes from hysteresis losses due to the flux entry into and exit from the superconducting tape during the up and down swings of the magnetic field. We have calculated coupling losses as a function of frequency and temperature-dependent time constant. Experimental data are analyzed by comparing them with the calculated curves. From the DC field dependence of the AC susceptibility, we obtained the irreversibility line.