AC Transport Losses Calculation in a Bi-2223 Current Lead Using Thermal Coupling With an Analytical Formula

International audienceWhen a current lead is fed with an alternating current, the temperature rise created by the losses tends to reduce the current carrying capacity. Thus, if the amplitude of the current exceeds the value of the critical current, the losses become large and thermal heating considerable. In this paper, the voltage-current characteristics of a Bi-2223 current lead have been measured at temperatures from 4.2 K to the critical temperature (about 108 K). These characteristics make it possible to determine Ic(T) and n(T) using then to calculate the AC transport losses with the help of an analytical formula. This analytical formula allows to easily obtain the thermoelectric balance point of the system, when the losses and the temperature do not vary any more. Moreover, a maximum value of the current transport amplitude, beyond which the balance point does not exist, is detected. Indeed, the system is not stable and the superconducting current lead may quench. Finally, the experimental results are compared with the results of both a numerical and an analytical model able to determine the losses below and above Ic