A Study on Determining Charging Current Waveform to Reduce Screening Current Induced Field in HTS NMR Magnets

In this paper, we present a method for determining the appropriate charging current waveform to mitigate the screening-current-induced field (SCF) in an NMR class HTS magnet. It has been observed that screening currents degrade the magnetic field quality of NMR class HTS magnets, and the extent of this degradation varies depending on the charging current waveform. We developed a simulation program to predict the effects of screening currents when applying specific charging current waveforms to given HTS magnets. Using the program, we were able to determine which current waveforms are most suitable for a given HTS magnet. To validate the performance of the program, we applied the same current waveforms to the actual NMR class HTS magnet and measured the central magnetic field. We compared the experimental results with the simulations and confirmed that they were nearly identical. This technique is expected to allow us to determine the most suitable charging current waveform for reducing screening currents before conducting time-consuming and resource-intensive charging experiments.