The analysis of the initial magnetic field decay in the persistent current mode

Abstract

This paper deals with the initial magnetic field decay for a large scale superconducting magnet e.g. NMR/MRI magnet. The high resolution image can not be obtained during the periods of the initial field decay. It is known that all superconducting materials have the property of diamagnetism. This diamagnetism is usually explained with the concept of screening current. We assumed that the existence of the screening current makes the current distribution in the superconducting wire non-uniform. The current distribution in the energizing state is different from the distribution in the steady current state in view of its pattern. The initial magnetic field decay is caused by the change of the current distribution between energizing state and persistent current mode. In this paper the theoretical analysis for the current distributions has been carried out for each state. The experiments have been carried out for various transport currents in order to verify the theoretical analysis. Through experiments, It was found that the initial field decay is small at the higher transport current. At the end of paper a method able to eliminate effectively the initial magnetic field decay is suggested.