Simulation of Screening Current Reduction Effect in REBCO Coils by External AC Magnetic Field
Second-generation high-temperature superconducting (HTS) tapes have been examined for applications, such as nuclear magnetic resonance, MRI, and accelerators. Each of these applications requires a precise magnetic field profile. However, screening currents induced while charging an HTS magnet degrade its magnetic field quality. Techniques to reduce the screening current effect have been proposed in the literature. One of the means to reduce screening currents is to apply an ac magnetic field using a “shaking magnet.” The shaking effect enhances the quality of magnetic field by reallocating the screening currents inside HTS tapes. Although some experiments to study the shaking field effect were reported, the current distribution inside HTS tapes has not yet been clarified by simulation. This paper presents the simulation results for an ac magnetic field applied to a REBCO tape to reduce the influence of screening currents. In addition, we investigated the influence of the angle of applied ac magnetic field at the magnet center. The area of negative current density is also shown. From the simulation results, we conclude that a shaking field applied at an angle between 10° and 30° is effective to reduce the screening current effect.