Peltier current lead experiment and their applications for superconducting magnets

Abstract

Many applications of superconductivity are studied because they are basically nondissipative systems; however, electric power is spent to keep them at low temperature. If heat leakage is high, the advantage of the superconductivity will be reduced or disappear, and therefore we must reduce the heat leakage as much as we can in the actual system. The Peltier current lead (PCL) was proposed to reduce heat leakage from the electric circuit of the superconducting magnet system. PCL is composed of thermoelectric semiconductors, metal leads, and high temperature superconducting (HTS) leads. Bismuth–tellurium alloys (BiTe) are used as the thermoelectric semiconductors in the experiment, and these are placed on the room temperature side. Optimum design of the PCL is conducted to solve a heat leakage equation, and depends on the transport parameters such as thermal conductivity, electric resistivity, and Seebeck coefficient of the materials of the PCL. The thermal conductivity of the BiTe is about 0.4% of the copper’s, and we can expect the Peltier cooling by using this material. Therefore, we can expect the large temperature difference of the BiTe and reduce the heat leakage. The experiment has been done and the cold-end temperature of the thermoelectric BiTe is around 200 K both in the experiment and the numerical calculation. The temperature difference of 4 mm thickness of the BiTe exceeds 70 K for 150 A in both the experiment and the calculation. Therefore, the principle was proven in the experiments, and the reduction of the heat leakage is up to 35% for the current lead included in the HTS current lead. Here, we also mentioned and proposed the various types of the PCL for the different kinds of superconducting magnet systems in this article.