Comparative thermometric and electric measurements of self-field AC losses in Ag-sheathed PbBi2223 tapes

A method for the thermometric measurement of the self-field AC losses of Ag-sheathed PbBi2223 tapes is described. This technique determines the loss by measuring the temperature profile associated with the losses, along the length of a vacuum insulated tape with each end maintained at a fixed base temperature. In practice the samples were placed in a vacuum capsule immersed in a liquid nitrogen bath. By ensuring the proper cryogenic conditions and with the use of a sensitive diode thermometer self-field losses between 7 μWm^-1 and 4 mWm^-1 have been measured. Comparisons with the electrical measurement technique show a good correspondence between the two methods. The effect, on the self field AC losses, of an inhomogenous distribution of critical current along the length of the tape is also discussed. Measurement of the frequency response of the losses show the importance of the eddy currents induced in the silver sheath. It is shown that these eddy currents are mainly due to the effect of the perpendicular component of the self field.