On minimizing the heat leak of current leads in cryogenic vacuum systems

Electronic devices such as infrared detectors in remote sensing instruments are frequently placed in cryogenic vacuum systems, such that the ratio of signal to noise can be enhanced. The heat leak of leads supplying usually small electric current to these electronic devices is a critical issue in system designs. Cu is a typical material for current leads. In this work, however, we suggest employing the Peltier current lead to lower the heat leak. It comprises a thermoelectric element and a Cu lead at the hot and cold ends, respectively. In considering the heat radiation between Cu leads and the vacuum vessel, both all-Cu and Peltier current leads are optimised so as to minimise their resulting heat leaking into cryogenic vacuum systems. Moreover, temperature-entropy (T-s) diagrams are constructed to track the actual thermodynamic processes in the two types of current leads. The heat leak of a current lead in the presence of heat radiation can be easily identified from the simple 2-D T-s plane. It is also proved that the effect of heat radiation on the heat leak of current leads is usually negligible.