Preliminary Mechanical Analysis of a 9.4-T Whole-Body MRI Magnet

Abstract

A 9.4-T/800-mm superconducting magnet for wholebody magnetic resonance imaging system has been designed and will be constructed from NbTi conductors. Main coils wound on five aluminum alloy formers provide the center field strength of about 9.4 T. In addition, compensation coils wound on another aluminum alloy former are used to improve the field uniformity of the imaging region. The operating point of the inner main coil is very close to the critical properties of its wire, and its temperature margin is about 0.4 K. It is necessary to know the mechanical stress in the main coils during all operating conditions. The mechanical behavior of the main coils during winding, cooldown, and energizing is analyzed. The effects on mechanical disturbances are predicted, and one available method is proposed to reduce premature quench. In addition, the dimension variations and position changes due to pretension, thermal contraction, and magnetic compression are present. Index Terms-Magnetic resonance imaging (MRI) superconducting magnet, Mechanical disturbance, mechanical stress. 1051-8223

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

“…The coil bundles are solved for all three processes-winding, cooldown and electromagnetic excitation. There are well verified existing analytical approaches [33,34,[36][37][38] to model winding, thermal cool down [39] and electromagnetic charging [31,[40][41][42][43][44], but the computational approach based on FEA is well favored considering orthotropic material approximation, boundary conditions, geometric complexity, and multivariate elastic moduli of wire and mandrel. Hence, while employing FEA analysis; shifting from the wire length scale to the coil bundle length scale makes the problem multiscale and modeling the coil bundle for electromagnetic excitation stress-strain turns the model into multiphysics modeling.…”

“…One approach to address the prestressing of the wire is to change the effective elastic modulus of the material as the wire is prestressed during winding around the mandrel [39]. Several other methods were also investigated in which each layer of a coil bundle is approximated as concentric thin cylinders [33,38]. However, all of the analytical approaches are based on a stress-strain relation, which takes the form of Hooke's law when simplified.…”

“…Since the stress in the axial direction of the bundle (direction 2 of wire) is negligible compared to the applied winding tension, the plane-stress approximation is more appropriate than the plane-strain [39]. When a layer of the bundle is wound with pretension, the applied radial pressure on the lower layers can be calculated by considering each layer of a coil as a concentric homogeneous cylinder using the following equation [33,38].…”

“…It is critical to understand the strain development in magnetic coils of MgB 2 because of the low failure strain of the material. While multiscale and multiphysics FE analysis of NbTi superconducting magnets has been carried out by researchers [32][33][34][35][36][37][38], mechanical strain analysis of a conduction cooled MgB 2 based superconducting solenoid magnet is yet to be explored.…”

A non-destructive method for detecting turn-to-turn resistivity distribution in NI REBCO coils

“…In fact, the TTRD of NI coils is affected by various factors including surface condition [27], temperature [12], number of thermal cycles [2] and turn-to-turn contact pressure [1] which is influenced by winding tension [28], thermal stress [28] and electromagnetic force [29]. Some studies [28,[30][31][32][33] have shown that even if the coil is wound with uniform pre-stress, the TTRD of the coil still exhibits a non-uniform distribution. In some instances, a non-uniform distribution of TTRD is intentionally introduced in NI coils to balance the self-protection capability with the charging time [34,35].…”