Peltier Current Leads For Superconducting Direct Current Devices

As a connecting superconducting devices at cryogenic temperature with power sources operating at room temperature, current leads cover a wide temperature range and are the major heat leakage source during operation. A Peltier current lead (PCL), consisting of thermoelectric semiconductors inserted into a pure copper lead at its room temperature side, can effectively reduce heat leaks and lower operational costs, which is a significant breakthrough for the solution.This thesis focused on design and fabrication of 100-A-class PCLs, moving towards kA class. The initial range of length and cross sectional area ratio of the current lead was calculated with the iterative method and the quasi-analytic method, providing the range for next analysis. A two dimensional model was built by employing thermoelectric modules of Comsol Multiphysics and thermoelectric properties of materials, then the optimization of current leads was completed for the purpose of minimum heat leak. Taking into account cooling methods at warm sides of current leads, models with natural air convection or water cooling modes were established. And optimized solutions were compared for choosing one. Current leads of different structures were analyzed for expanding the application range.Then 100-A-class PCL samples and chilly water apparatuses were finished, and we carried out heat leak experiments of the two modes at 77 K. Fitting method is adopted for processing measured data. Optimal current of water cooling mode was obtained, verifying the success of chilly water apparatuses and 100-A-class PCLs. The effect of cooling methods on heat leaks and carrying capacity of the lead was demonstrated by comparing the performance between the two modes. Numerical models were also used against experiments. Finally, according to the thermal characteristics of the two modes, the current lead with switching modes was envisaged for the variable current system.