OPTIMIZATION OF TWO-STAGE CONDUCTION COOLING FOR HTS CURRENT LEADS

摘要

An optimal two-stage cooling method for HTS current leads is developed to minimize the required refrigerator power input. The lead is a series combination of a normal metal conductor at the warmer part and an HTS at the colder part. The cold end of the HTS lead is conduction-cooled by a cryocooler and heat is also intercepted at an intermediate axial location. Mathematical expressions are derived for the required refrigerator power per unit current for typical cryocoolers. It is demonstrated that both the current density and the intercept temperature should be optimized simultaneously to minimize the refrigerator power per unit current and maintain the HTS in a superconducting state. In addition, it is verified that heat should be intercepted at the joint of the two parts or at an optimal axial position of the metal lead for the minimum refrigerator power. The design conditions for the two-stage cooling are quantitatively presented with the effects of the magnetic field and the stability margins of the HTS lead, when the cold end temperature is 4 K or 30 K.