Investigation of the Relaxation of Persistent Current in Superconducting Closed Loops Made Out of YBCO Coated Conductors

Abstract

Coated conductors allow the fabrication of closed superconducting loops of arbitrary size. Various mechanisms can play a role in the decay of a persistent current in one such loop and in an assembly of multiple loops magnetically coupled with each other. We report recent experimental results on the relaxation rate of the persistent current in an assembly of closed superconducting loops made out of the currently manufactured coated conductors. One of the main goals of this study is to find the effective ways to control the relaxation rate so as to make it small enough to enable such high temperature persistent magnets to be considered as potential alternatives for energy storage, MRI magnets, and magnetic levitation applications. Here we report the effect of appropriately modified current sweep reversal method on the relaxation rate.Index Terms-Coated conductor, current sweep reversal method, MAGLEV, MRI, persistent current, relaxation rate, SMES, 2G HTS.

Magnetization of the joint-free high temperature superconductor (RE)Ba2Cu3Ox coil by field cooling

“…This resistance can result in a measureable degradation of the induced current and therefore the trapped field. 30 Fig. 6 shows the decay of the trapped field after the background field drops to zero, in which the ramping time of the magnetization field varies from 1 s to 60 s. Here, the 'magnetization filed' is the background magnetic field in which the coil is exposed at the beginning of the field cooling operation.…”

“…High stable fields are trapped in these tests. 8,[26][27][28][29][30] Researches have also focused on the field shielding function of this joint-free coil, which has been validated by experiments. 13,14 Both the field trapping and filed shielding result from induced current, and they share a same underlying mechanism.…”

Experimental Setup for the Investigation of Superconducting Persistent Current

“…2, the radius of the coil former was chosen to be R ≈ 3 cm. The total length of the loop 8In another example, the length of the sample previously used in experiments 10 was L = 11 cm with ∆ = 1 cm. Then, the maximum radius of the coil former, Eq.…”

“…Figures 8 and 9 show the dimensions of Teflon holders and the superconductor coil assembly originally designed, along with a separate copper coil that is used to generate an external magnetic field to induce a super current in the superconducting coil. As a matter of fact, in those experiments 10,11 carried out at the Naval facility, a built-in magnet was actually used instead of the copper coil in order to accurately control the magnetic field strength and correlate the filed strength with superconducting current level. Fig.…”

“…Although there are other substantial issues to be overcome with respect to HTS SMES application, which requires persistent superconducting current with no or minimum energy dissipation, we focus our effort on only one of the issues, namely, persistent current behavior in a true closed loop without any physical non-superconductive joint. 9 The investigations of persistent current characteristics have been reported elsewhere, 10,11 and this report documents only the part of the research effort in setting up the experiments for the investigation, which is generally not described in great details in regular journal publications.…”