Helium vapor-cooled brass current leads: Experimental and analytical results

This paper presents experimental and analytical results of a pair of helium vapor-cooled brass leads having a rated current, I_t, of 40 A, operated continuously below, at, and above 40 A. In Regime 1 (0<I≤I_t), the leads operate stably sustained by cooling that increases with I, in agreement with a theory originally developed for copper leads and modified for brass leads. In Regime 2 (I_t<I<I_2c, where I_2c is an upper limit current), the leads also operate stably. A simple theory has been developed to elucidate this stable operation in Regime 2. In addition to the original cooling term valid for Regime 1, the theory includes another term that increases as I². Agreement between theory and experiment for both regimes is quite good.