AC Losses of ReBCO Pancake Coils Measured by a Calorimetric Method

During a field ramp of a ReBCO magnet, the heat dissipated by conductor AC losses may affect the magnet operation temperature, and significantly increase the liquid helium consumption. Therefore, the calculation and measurement of AC losses of ReBCO coils are very important. Understanding the AC losses behavior of ReBCO coils will allow prediction of AC losses for future ReBCO magnets. In this paper, we measured AC losses of a stack of six ReBCO double pancake coils in varying external magnetic fields without transport current by a calorimetric method. The external magnetic field was provided by a 200 mm bore resistive magnet, which sweeps in 0-15-0 T cycles at different rates. The AC losses were measured by liquid helium boil-off from the cryostat containing the test coils. The measured AC losses are small and mostly from the coupling losses due to imperfections in turn-to-turn electrical insulation. The hysteresis loss contribution is below the detection limit due to the magnetic shielding of the radial field.