AC losses in HTS multi-pancake coils made of BSCCO-tape

We present measurements of AC losses in Bi-2223 multi-pancakes coils with different geometries. Measurements were performed at 77 K at frequencies ranging from 50 to 1600 Hz. The losses are found to depend strongly on coil configuration and linearly increase with increasing frequency. The centre pancakes in the coils exhibit larger AC losses than pancakes situated at the ends. Also, AC losses within pancakes depend on adjacent pancakes, even if kept in an open circuit state. The strong change of inductances of pancakes in multi-pancakes coils was observed in opposite to negligible change for single pancake. Introducing a gap between pancakes/ double pancakes can be used as a means of decreasing AC losses in multi-pancakes HTS coils.