Currents in series and parallel connections of small inner bore coils wound from Bi(2223)/Ag tapes and treated by the wind and react technique

A set of small inner bore (8.5 mm) single pancake coils was wound from mult ifilament Bi(2223)/Ag tapes using the 'wind and react' (W&R) technique. W&R means sintering heat treatment of the Bi(2223)/Ag tape wound to a pancake coil. During the winding procedure, the tape was insulated by a mixture of Al2O3 or ZrO2 powders with varnish. After the first sintering step (841 deg rees C/50 h), the printed insulation was easily removed and the tape with a clean surface was subjected to intermediate deformation by rolling. After the final heat treatment (841 degrees C/150 h), the coils were impregnated by epoxy resin. Electrical measurements of individual pancakes certified th e good quality of interturn insulation. Some variations of transport curren ts among the pancakes were measured. The selected coils were connected in s eries or parallel and current distribution and I-V curves of individual coi ls were measured. Comparison of both connections is discussed in detail. Th e results of a small magnet arranged by connection of five single pancake c oils with partial compensation of the radial field component is also presen ted. The compensation of the radial field component allows us to increase t he magnetic field in the bore axis by 215%. Further lowering of temperature to 65 K allows us to generate a magnetic field nearly five times higher th an in the case of the non-compensated winding at 77 K.