A 7 T superconducting magnet was designed and under fabrication for animal magnetic resonance imaging (MRI). The magnet includes two primary coils, four compensating coils and three shielding coils. All the coils together produced a homogeneous magnetic field over an imaging sphere with diameter 0.130 m and the stray field was actively-shielded within an area at longitudinal length 3 m and radial length 2 m.
The magnet coils adopted NbTi superconducting wire with length 80.86 km and volume 0.11 m3. The operating current is 180 A for the target magnetic field strength. Under the electromagnetic circumstances, the maximum hoop stress reaches 106 MPa. The maximum magnetic field strength is 7.18 T with a current margin 83.8% and temperature margin 1.10 K at 4.2 K. The inductance of the magnet is 213.7 H and magnetic energy is 3.5 MJ.
The magnet coils were wound on four bobbins, where the first-layer primary coil and the second-layer primary coil occupied two individual bobbins, the four compensating coils were laid on one common bobbin and the three shielding coils also shared one bobbin. The fifth bobbin between the compensating coils layer and the shielding coils layer was scheduled to arrange the superconducting shim coils. The mechanical components were assembled with two end plates with 16 pull rods. The whole structure was immersed in liquid helium and surrounded in a cryostat to keep the superconducting wire at an extremely-low temperature environment.
The developed superconducting magnet has a 300 mm warm bore where a dedicated gradient assembly and radio-frequency assembly will be installed to establish a final imaging platform.