Electrothermal Behavior of the Joint of Binary Current Lead of Conduction-Cooled Magnet

A 6-T cryogen-free NbTi magnet system with a warm bore has been developed using a two-stage cryocooler (CCR). The binary current lead is one of the main components of any conduction-cooled magnet system. The heat flow scheme through the binary current leads greatly determines the operating points and the thermal stability of the magnet system. A pair of binary current leads has been developed for a 102-A current to achieve a 6-T field. The thermal interception of a binary current lead along with their electrical isolation to the corresponding cooling stages of the CCR greatly influences the electrothermal behavior of the lead, which eventually influences the stability of the magnet. Low-electrical-resistance and low-thermal-resistance joints have been developed for the binary current leads. The equilibrium temperatures are 37.75 and 4.55 K, respectively, for the first- and second-stage lead joints at zero current. In addition, the corresponding equilibrium temperatures of lead joints are 42.04 and 6.55 K at 102-A current. The average thermal impedance of the corresponding joints is measured to be 0.6 and 13.7 K/W.