Characteristics of Conduction-Cooled Binary Current Leads Used in Cryogen-Free Probe Station

The binary current lead cooled by a two-stage cryocooler for an NbTi superconducting magnet used in cryogenic probe station was designed, fabricated, and tested. The current lead was composed of metal and a high-temperature superconductor (HTS) element. The temperatures at the joints between metal and the HTS element as well as between the HTS element and the NbTi coil were measured during cool down and the magnet charging process. The cryogenic loads at each stage were derived from the measured temperature and cooling capacity curve of a cryocooler. An HTS current lead was bolt jointed to the metal element and NbTi coil at both ends, so contact resistance was unavoidable. When the superconducting magnet was charged, the temperature at each joint increased with supplied current depending on the amount of heat generation resulting from the contact resistance. The cryogenic load was corrected because additional loads such as support conduction and thermal radiation were affecting the temperatures at each stage. The correlation of heat generation through the binary current lead was investigated in terms of supplying current, contact resistance, and cryogenic load.