Screening Current Behaviors of an Intra-Layer No-Insulation Magnet in Self Field and Background Field

A 500 MHz high temperature superconducting (HTS) and low temperature superconducting (LTS) hybrid NMR magnets with conduction cooling has been designed in the paper, in which the HTS insert magnet is designed and fabricated with an intra-layer no-insulation (LNI) layer-wound coil structure. An equivalent circuit model considering layer-wound coil helical structure coupled with a stacked homogenization T-A model is used to study the screening current behaviors and magnetic field homogeneity of the HTS-LTS hybrid NMR magnet. It can be found that the maximum value of the time constant of the LNI layer-wound coil is only determined by the copper foil resistance, which ensures a smaller charging delay. The screening current induced by self field and some special background field, which does not change the original radial magnetic flux direction of the LNI HTS magnet, optimizes the magnetic field homogeneity. The screening current induced by the LTS compensation coils is the reason for the deterioration of magnetic field homogeneity. Then, we use the screening current property to readjust the parameters of the background magnets, which make the homogeneity of the NMR magnet optimized.