A distinct method to eliminate the induced voltage in AC loss determination without phase control

摘要

AC loss is often considered one of the most important design parameters that guide the fabrication of superconducting devices. Thus, the electrometric method to determine AC loss of superconductors is crucial. Usually, the obtained voltage contains the resistive part and the inductive part. If the induced voltage is large, it will make the result very sensitive to the phase error, and hence, a compensating method is usually adopted. However, phase determination was still needed in the previous studies. In this work, we present an approach to precisely eliminate the unknown induced voltage of the sample just by alternating the inductance of the compensating coil. By determining the minimum of the sample voltage, where the induced voltage of the sample is precisely compensated, the AC loss is then able to be calculated without phase control. The principle of the presented method is strictly certified with the mathematic derivation, along with experimental proof. Current and frequency dependent inductance and loss resistance are obtained naturally. The result reveals that the ratio of induced voltage to resistive voltage decreases exponentially with an increase in current. We also found that the resistance of the CC is determined by both applied currents and frequencies. To universally describe these relations, the cycle resistance r is defined by an exponential function, allowing calculating AC loss with different frequencies just through the data of one frequency, which greatly facilitates the testing process. This method is also expected to be utilized in AC loss measurements for superconducting cables and coils.