ENERGY LOSSES IN INDUCTIVE SUPERCONDUCTING SOLENOIDS WITH TIME VARYING TRANSPORT CURRENTS

A helium boil-off technique was used to measure the energy losses in inductive, multi-layer superconducting solenoids carrying time varying transport currents and comparisons are made with existing loss models. The coils were wound using commercially available, multifilament NbTi conductors of varying filament sizes, twist rates, and conductor geometries. Loss measurements were made for pulsed dc and 60 Hz ac transport currents. The pulsed dc data were taken as a function of peak magnetic field at 10 Hz and as a function of frequency (1-10 Hz) at a constant magnetic field. The 60 Hz ac loss data were taken as a function of magnetic field. Conventional loss models are reviewed and expressions for coil losses for full and partial penetration are developed. The loss data are compared to calculations based on these expressions, but the poor agreement in the case of pulsed dc data indicated that our data was taken for peak fields that (varying from 0.2 T to 1.5 T) correspond to a transition between dominance of full or partial penetration. This data agreed well with a model developed by Ashkin hat predicted such a large transition region. The 60 Hz losses were found to have a hysteresis and a matrix current component. The hysteresis component was found to agree with an expression reported by Sumiyoshi et al. which was developed using the Irie and Yamafuji phenomenological model for flux pinning.