Determination of the time constant from the time development of the induced magnetic field above superconducting cables

摘要

We derived the relation between the time position t_m, at which the maximum of the difference between the magnetic induction at the sample centre and the induction of the applied magnetic field appears, and the time constant τ of superconducting cables or normal metals. This enables the determination of the time constant (which is proportional to the coupling or eddy current losses at low frequencies) from the experimental results in a very simplified procedure. Very good agreement is achieved between experimental results and the simplified theory. It is shown that the time constant of the measured samples can be in a wide range (compared with the time constant of the applied magnetic field) to ensure sufficient signal for detecting experimentally the difference between the magnetic induction at the sample centre and the induction of the applied magnetic field. In addition, for a wide range of parameters used, a very simple relation between the time constant of the structure and the time constant of the applied magnetic field is given.