Coupling current and hysteresis losses of Bi2212 round wires with twisted filaments

AC loss measurements have been carried out on Bi2212 round wires of different twist pitches. With systematical variation of sample temperature (5 K-70 K) and ac field amplitude (? 0.2 T) as well as frequency (20 Hz-2 kHz) , this work shows (1) the full coupling of the non-twisted wire, (2) the uncoupling of sub-wires by twisting at moderate pitch up to 12 mm, (3) a relatively short time constant of milliseconds for the coupling current due to a high transverse resistivity, and (4) an effective (de)coupling diameter of 0.4 mm about 1.6 × of sub-wire bundles. The results suggest a promising potential for improving filament decouplin