Eddy current heating in micro-SMES bus-bars

Results from numerical models and theoretical analyses are presented that describe the development of eddy current heating in copper bus bars, both with and without superconducting elements, in response to the rapid decay of current in a nearby superconducting magnet such as in micro-SMES systems. The analysis differs from those available in the open literature in that the change of magnetic field is neither instantaneous, nor sinusoidal. We especially investigate eddy current heating in the regime where the field decay time is on the order of the current diffusion time constant. It is found that the self-inductance of the copper bus bar contributes significantly to the time dependent heat generation. Analytical results are compared to experimental data in the form of subsequent temperature excursions of a liquid helium cooled copper bus, in response to field ramp rates on the order of 1.5 tesla/second.