Study of frequency dependent AC loss in Bi-2223 tapes used for gradient coils in magnetic resonance imaging

The use of Bi-2223 tapes as the material for gradient coils in Magnetic Resonance Imaging (MRI) is promising because Bi-2223 tapes have very high critical current and very low power loss. Frequency dependent AC loss in Bi-2223 tapes was measured at the operating frequencies of gradient coil from 200 Hz up to 2000 Hz. It is found that AC loss decreases with frequency below 800 Hz and then increases from 800 Hz to 2000 Hz. The contribution of hysteresis loss, eddy current loss and resistive loss to the total AC loss are investigated individually. The power-law E-J characteristic of tapes and position dependent current distribution are considered as the major reasons for the frequency dependence below 800 Hz. Eddy current loss should account for the increasing power loss with frequency above 800 Hz.