A customized electric heater to mitigate screening current by optimal control on temperature distribution in a high-temperature superconductor coil

Abstract

The so-called screening current in a high temperature superconductor (HTS) is a well-known phenomenon that has detrimental effects on performance of an HTS magnet. To date, many research efforts have been devoted to suppressing screening current in an HTS magnet. Here, we report a customized electric-heater, named “Thermal Eraser,” to mitigate the screening current. The key idea is to optimally control the spatial temperature distribution in an HTS magnet using the customized heater and the consequent temperature-dependent local critical current of HTS wires of the magnet. To validate the idea, a Thermal Eraser was designed, constructed, and installed in an actual single-pancake HTS coil. The Thermal Eraser with the test coil system was operated at temperatures ranging 7–40 K in our in-house conduction-cooling cryogenic facility. The feasibility of the Thermal Eraser was demonstrated in terms of two aspects: (1) creation of the designated spatial temperature distribution within the HTS test coil as designed and (2) quantitative evaluation of its effectiveness to mitigate screening current using both experimental and numerical results. We confirmed that the screening current induced field in the test coil was reduced by 0.6 mT after activation of the Thermal Eraser, which implies 60% reduction of screening current in the HTS test coil. The results demonstrate that the Thermal Eraser is a viable option to effectively reduce the screening current in an HTS magnet.