Evaluation of Influence of External Magnetic Disturbance on Superconducting Magnet taking Conservation of Linkage Flux into Account

Abstract

External magnetic disturbance has great influence on the quality of the image obtained by magnetic resonsnceimaging system because it causes a drift of magnetic resonance frequency. When a superconducting magnet in persistent current mode operation is exposed to external magnetic disturbance, current in the coil varies to keep linkage flux constant. The conventional analysis is usually formulated on condition of constant current and does not give correct evaluation of drift of magnetic field in the magnet. This paper proposes a method of numerical analysis of magnetic field considering conservation of linkage flux in a superconducting magnet under persistent currnt mode operation. This method is applied to evaluate drift of magnetic field in a supercconducting magnet for magnetic resonance imaging due to external magnetic disturbance. The results of the anlysis show good agreement with the experimental results.