Induced current in a Bi2Sr2CaCu2Ox superconductor tube

Experiments were conducted to measure the induced current in a high-temperature Bi2Sr2CaCu2Ox superconductor tube that was excited by an external coil driven by an AC sinusoidal voltage source. Experimental data were obtained for tests without and with an iron core inside the superconductor tube. All of the tests were conducted at 77 K and an excitation frequency of 60 Hz. The results showed that immediately after field penetration, the induced current (RMS value) decreased from the critical current, then began to recover, and eventually approached the critical current again at a high excitation current. Before field penetration, the induced current was mainly shielding current, which is 180 degrees out of phase with the excitation current. After field penetration, the induced current consisted of two parts, a shielding current that led the excitation current by 180 degrees and an inductive current (Faraday's law) that led the excitation current by 90 degrees. The presence of the iron core amplified the drop in induced current immediately after field penetration and delayed the growth of the inductive current after field penetration. Published by Elsevier Science Ltd.