Thermal Analysis of a Head-Only 1.5 T Magnetic Resonance Imaging Superconducting Magnet

A 1.5 T head-only magnetic resonance imaging (MRI) superconducting magnet with liquid helium (LHe) bath-cooling using NbTi wire has been designed and is being constructed in Wuhan National High Magnetic Field Center (WHMFC). The magnet consists of 9 discretized coils, including five main coils and two bucking coils, wound on two separate stainless steel 304 formers. The magnet is designed to operate at 510 A with a peak field below 3.0 T, load line controlled below 50%, and temperature margin above 1 K. It is critical to accurately evaluate the thermal load of the superconducting magnet system to ensure its zero boil-off normal operation since LHe is very expensive and non-renewable. A detailed heat load model is presented in this paper. The heat load is evaluated by finite element analysis, theoretical formula calculation and empirical formula calculation, which fully considers conduction, radiation and convection. The results indicate that the total head load of the second stage is approximately 0.237 W and that of the first stage is about 20.26 W which is well below the cooling power of the SRDE-412D4 cryocooler used in the magnet system.