Estimation Method of Optimal Amount of Overshooting Current for Temporal Uniform Magnetic Field in Conduction-Cooled HTS Coils

We investigated a suitable excitation method to suppress the shielding magnetic flux density attenuation using only the one-time excitation of a REBCO coil, which was cooled by a refrigerator. We investigated the operating temperature and current load factor dependences of the variation rate of the shielding magnetic flux density immediately after an overshooting process. Regardless of the operating temperature and current load factor, the variation rate of the shielding magnetic flux density decreases with the magnitude of overshooting current and changes from a positive value to a negative value. In each current load factor, the ratio of the optimal overshooting current to the critical current of the REBCO coil becomes almost identical regardless of the operating temperature. Based on these results, we devised a suitable overshooting current waveform to suppress the shielding magnetic flux density attenuation in the REBCO coil cooled by the refrigerator. The overshooting current was repeated to the coil in a one-time excitation; the amount of overshooting current was gradually increased until the variation rate of magnetic flux density was changed from positive to negative. Using this current waveform, we can suppress the shielding magnetic flux density attenuation in the conduction-cooled REBCO coil using only a one-time excitation.