Investigation on transient characteristics of current leads for superconducting magnet

Abstract

The current lead acts as dominant heat input source into superconducting system, by conduction through it and Joule heating within it. Even though the optimized current leads were often designed to minimize this heat inputs, the overloaded current lead is more efficient for pulse mode operation because it has less cross sectional area and less time-averaged heat input than optimized one. Since the overloaded current lead has its limitation by hot spot temperature, it is important to estimate the hot spot temperature for appropriate overloading factor in pulse mode operating current lead. In this thesis, the transient numerical analysis is performed to estimate the hot spot temperature because the current lead is not steady but transient state in the pulse mode. Also, the present numerical modeling considers that there is temperature difference between the copper lead and the helium vapor flow and the heat is transferred by forced convection between them. Moreover, this numerical modeling is compensated and validated by the experiment with commercially available 100 A current leads. The numerical modeling in this thesis describes thermal characteristics of overloaded current leads more accurately than conventional steady state analysis. Proper design of overloaded current leads is suggested by indicating the appropriate overloading factor in the pulse mode operation.