A multiscale and multiphysics model of strain development in a 1.5 T MRI magnet designed with 36 filament composite MgB₂superconducting wire

Abstract

High temperature superconductors such as MgB2 focus on conduction cooling of electromagnets that eliminates the use of liquid helium. With the recent advances in the strain sustainability of MgB2, a full body 1.5 T conduction cooled magnetic resonance imaging (MRI) magnet shows promise. In this article, a 36 filament MgB2 superconducting wire is considered for a 1.5 T full-body MRI system and is analyzed in terms of strain development. In order to facilitate analysis, this composite wire is homogenized and the orthotropic wire material properties are employed to solve for strain development using a 2D-axisymmetric finite element analysis (FEA) model of the entire set of MRI magnet. The entire multiscale multiphysics analysis is considered from the wire to the magnet bundles addressing winding, cooling and electromagnetic excitation. The FEA solution is verified with proven analytical equations and acceptable agreement is reported. The results show a maximum mechanical strain development of 0.06% that is within the failure criteria of −0.6% to 0.4% (−0.3% to 0.2% for design) for the 36 filament MgB2 wire. Therefore, the study indicates the safe operation of the conduction cooled MgB2 based MRI magnet as far as strain development is concerned.

Conceptual designs of conduction cooled MgB2 magnets for 1.5 and 3.0 T full body MRI systems

“…Similarly, the technique has been applied to MgB 2 wire [54] and was used to estimate the homogenized properties of the three types of MgB 2 wire used in this paper. A cross section of an actual wire and a CAD model representation used to calculate the homogenized wire model are presented in figure 11.…”

“…[55], a variety of composite MgB 2 wires were tested in pure tension, and the results are consistent with the notion that the mechanical hoop stress is an important consideration in coil winding. Thus, this section focuses on the first principal mechanical strains [54, 56]. The strain failure limit for the wires used in this paper is estimated to be 0.4% [55].…”

“…The strain failure limit for the wires used in this paper is estimated to be 0.4% [55]. However, a magnet design is considered viable if the calculated stress is below 0.2% [54], which provides a margin of error in the estimation of the strain failure limit.…”

“…The maximum strain is attributed to the Lorentz force development, since the Lorentz force peaks near the location of maximum magnetic field during the electromagnetic charging. Given the strain limit criteria of 0.2% for the magnet design [54], it is expected that the magnet will operate safely when electromagnetically charged.…”

“…The material properties of the composite wires used in the simulations (figure 14) are calculated using the material properties of the individual components taken from the published references tabulated in [39, 54, 59]. Compared to the wire with Monel (Wire #1542), the thermal conductivity of the wire with Glidcop (Wire #1542G) is significantly higher while the electrical resistivity of the Glidcop wire is significantly lower.…”